refactor(codemode): type program values as Value

refactor(codemode): let each built-in object answer for itself
feat(codemode): add toLocaleString, Error.isError, and Map.getOrInsert (#50098 )
2026-09-20 23:57:40 +00:00 · 2026-09-20 11:03:16 -05:00 · 2026-09-20 10:45:53 -05:00 · 2026-09-20 10:23:23 -05:00 · 2026-09-20 14:37:06 +00:00 · 2026-09-20 13:36:51 +00:00
136 changed files with 3281 additions and 3209 deletions
@@ -32,7 +32,7 @@
    },
    "packages/ai": {
      "name": "@opencode/ai",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@aws-sdk/credential-providers": "3.1057.0",
        "@opencode/schema": "workspace:*",
@@ -54,7 +54,7 @@
    },
    "packages/app": {
      "name": "@opencode/app",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@corvu/drawer": "catalog:",
        "@dnd-kit/abstract": "0.5.0",
@@ -111,7 +111,7 @@
    },
    "packages/cli": {
      "name": "@opencode/cli",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "bin": {
        "opencode2": "./bin/opencode2.cjs",
      },
@@ -175,7 +175,7 @@
    },
    "packages/client": {
      "name": "@opencode/client",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/protocol": "workspace:*",
        "@opencode/schema": "workspace:*",
@@ -201,7 +201,7 @@
    },
    "packages/codemode": {
      "name": "@opencode/codemode",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "acorn": "8.15.0",
        "effect": "catalog:",
@@ -214,7 +214,7 @@
    },
    "packages/console/app": {
      "name": "@opencode/console-app",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@cloudflare/vite-plugin": "1.15.2",
        "@ibm/plex": "6.4.1",
@@ -250,7 +250,7 @@
    },
    "packages/console/core": {
      "name": "@opencode/console-core",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@aws-sdk/client-sts": "3.782.0",
        "@jsx-email/render": "1.1.1",
@@ -277,7 +277,7 @@
    },
    "packages/console/function": {
      "name": "@opencode/console-function",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@openauthjs/openauth": "0.0.0-20250322224806",
        "@opencode/console-core": "workspace:*",
@@ -294,7 +294,7 @@
    },
    "packages/console/mail": {
      "name": "@opencode/console-mail",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@jsx-email/all": "2.2.3",
        "@jsx-email/cli": "1.4.3",
@@ -318,7 +318,7 @@
    },
    "packages/console/support": {
      "name": "@opencode/console-support",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@cloudflare/vite-plugin": "1.15.2",
        "@opencode/console-core": "workspace:*",
@@ -338,7 +338,7 @@
    },
    "packages/core": {
      "name": "@opencode/core",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@ai-sdk/cohere": "3.0.27",
        "@ai-sdk/gateway": "3.0.104",
@@ -406,7 +406,7 @@
    },
    "packages/desktop": {
      "name": "@opencode/desktop",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@zip.js/zip.js": "2.7.62",
        "electron-context-menu": "4.1.2",
@@ -455,7 +455,7 @@
    },
    "packages/enterprise": {
      "name": "@opencode/enterprise",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@hono/standard-validator": "catalog:",
        "@opencode-ai/sdk": "1.18.21",
@@ -492,7 +492,7 @@
    },
    "packages/function": {
      "name": "@opencode/function",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@octokit/auth-app": "8.0.1",
        "@octokit/rest": "catalog:",
@@ -508,7 +508,7 @@
    },
    "packages/http-recorder": {
      "name": "@opencode/http-recorder",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@effect/platform-node-shared": "4.0.0-rc.112",
      },
@@ -527,7 +527,7 @@
    },
    "packages/httpapi-codegen": {
      "name": "@opencode/httpapi-codegen",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "effect": "catalog:",
        "prettier": "3.6.2",
@@ -540,7 +540,7 @@
    },
    "packages/latex": {
      "name": "@opencode/latex",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/plugin": "workspace:*",
        "@opentui/core": "catalog:",
@@ -554,7 +554,7 @@
    },
    "packages/merman": {
      "name": "@opencode/merman",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/plugin": "workspace:*",
        "@opentui/core": "catalog:",
@@ -569,7 +569,7 @@
    },
    "packages/plugin": {
      "name": "@opencode/plugin",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@ai-sdk/provider": "3.0.8",
        "@opencode/ai": "workspace:*",
@@ -608,7 +608,7 @@
    },
    "packages/plugin-browser": {
      "name": "@opencode/plugin-browser",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/plugin": "workspace:*",
        "@opencode/schema": "workspace:*",
@@ -638,7 +638,7 @@
    },
    "packages/protocol": {
      "name": "@opencode/protocol",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/schema": "workspace:*",
        "effect": "catalog:",
@@ -653,7 +653,7 @@
    },
    "packages/schema": {
      "name": "@opencode/schema",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@standard-schema/spec": "catalog:",
        "effect": "catalog:",
@@ -677,7 +677,7 @@
    },
    "packages/sdk": {
      "name": "@opencode/sdk",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/client": "workspace:*",
        "@opencode/core": "workspace:*",
@@ -698,7 +698,7 @@
    },
    "packages/server": {
      "name": "@opencode/server",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@effect/platform-node": "catalog:",
        "@effect/platform-node-shared": "catalog:",
@@ -720,7 +720,7 @@
    },
    "packages/session-ui": {
      "name": "@opencode/session-ui",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@kobalte/core": "catalog:",
        "@opencode/client": "workspace:*",
@@ -755,7 +755,7 @@
    },
    "packages/simulation": {
      "name": "@opencode/simulation",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/ai": "workspace:*",
        "@opencode/core": "workspace:*",
@@ -775,7 +775,7 @@
    },
    "packages/stats/app": {
      "name": "@opencode/stats-app",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@ibm/plex": "6.4.1",
        "@kobalte/core": "catalog:",
@@ -809,7 +809,7 @@
    },
    "packages/stats/core": {
      "name": "@opencode/stats-core",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@aws-sdk/client-athena": "3.933.0",
        "@planetscale/database": "1.19.0",
@@ -828,7 +828,7 @@
    },
    "packages/stats/server": {
      "name": "@opencode/stats-server",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@aws-sdk/client-firehose": "3.933.0",
        "@effect/platform-node": "catalog:",
@@ -874,7 +874,7 @@
    },
    "packages/theme": {
      "name": "@opencode/theme",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opentui/core": "catalog:",
        "effect": "catalog:",
@@ -888,7 +888,7 @@
    },
    "packages/tui": {
      "name": "@opencode/tui",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@opencode/client": "workspace:*",
        "@opencode/core": "workspace:*",
@@ -923,7 +923,7 @@
    },
    "packages/ui": {
      "name": "@opencode/ui",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@kobalte/core": "catalog:",
        "@pierre/diffs": "catalog:",
@@ -958,7 +958,7 @@
    },
    "packages/util": {
      "name": "@opencode/util",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@effect/opentelemetry": "catalog:",
        "@effect/platform-node": "catalog:",
@@ -991,7 +991,7 @@
    },
    "packages/web": {
      "name": "@opencode/web",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "@astrojs/cloudflare": "12.6.3",
        "@astrojs/markdown-remark": "6.3.1",
@@ -1032,7 +1032,7 @@
    },
    "services/update": {
      "name": "@opencode/update",
-      "version": "2.0.10",
+      "version": "2.0.11",
      "dependencies": {
        "jose": "6.0.11",
        "semver": "catalog:",
@@ -2,7 +2,7 @@
  "$schema": "https://json.schemastore.org/package.json",
  "name": "opencode",
  "description": "AI-powered development tool",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "private": true,
  "type": "module",
  "packageManager": "bun@1.4.2",
@@ -1,6 +1,6 @@
 {
  "$schema": "https://json.schemastore.org/package.json",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "name": "@opencode/ai",
  "type": "module",
  "license": "MIT",
@@ -19,6 +19,13 @@ export function mountBrowserPane() {
      session: "Alpha",
      mounted: true,
      visible: true,
+      url: undefined as string | undefined,
+      loading: false,
+      generation: 0,
+      delayNavigation: false,
+      pendingURL: undefined as string | undefined,
+      loadErrors: {} as Record<string, string | undefined>,
+      error: undefined as string | undefined,
      layouts: {} as Record<string, BrowserPaneLayout | undefined>,
    })
    const tabs = ["Alpha", "Beta"].map((name) => ({
@@ -47,13 +54,33 @@ export function mountBrowserPane() {
      opened: () => !!registrations.get(store.session),
      state: () => ({ tabs: tabs.filter((tab) => tab.title === store.session), focusedTabID: null }),
      tabs: () => tabs.filter((tab) => tab.title === store.session),
-      active: () => tabs.find((tab) => tab.title === store.session) ?? tabs[0],
+      active: () => {
+        const tab = tabs.find((tab) => tab.title === store.session) ?? tabs[0]
+        return {
+          ...tab,
+          url: store.url ?? tab.url,
+          loading: store.loading,
+          generation: store.generation,
+          loadError: store.loadErrors[store.session],
+        }
+      },
      registration: () => registrations.get(store.session),
-      error: () => undefined,
+      error: () => store.error ?? (store.loadErrors[store.session] ? "Request failed" : undefined),
      suspended: () => false,
      close: () => undefined,
      open: () => undefined,
-      command: () => undefined,
+      command: (command) => {
+        setStore("error", undefined)
+        if (command.type === "navigate" || command.type === "reload") setStore("loadErrors", store.session, undefined)
+        if (command.type === "navigate") {
+          if (store.delayNavigation) {
+            setStore("pendingURL", command.url)
+            return
+          }
+          setStore({ url: command.url, loading: false, generation: store.generation + 1 })
+        }
+        if (command.type === "stop") setStore("loading", false)
+      },
    }
    return (
      <>
@@ -64,6 +91,32 @@ export function mountBrowserPane() {
            {(name) => <button onClick={() => setStore({ session: name, mounted: name !== "Empty" })}>{name}</button>}
          </For>
          <button onClick={() => setStore("mounted", false)}>Unmount pane</button>
+          <button onClick={() => setStore({ url: "about:blank", loading: false })}>Blank page</button>
+          <button onClick={() => setStore({ url: "about:blank", loading: true })}>Loading page</button>
+          <button
+            onClick={() =>
+              setStore({ loading: true, generation: store.generation + 1, loadErrors: { [store.session]: undefined } })
+            }
+          >
+            Load current page
+          </button>
+          <button onClick={() => setStore("loadErrors", store.session, "ERR_CONNECTION_REFUSED")}>Failed page</button>
+          <button onClick={() => setStore("delayNavigation", true)}>Delay navigation</button>
+          <button onClick={() => setStore({ error: "ERR_BLOCKED_BY_CLIENT", pendingURL: undefined })}>
+            Block navigation
+          </button>
+          <button
+            onClick={() =>
+              setStore({
+                url: store.pendingURL,
+                pendingURL: undefined,
+                loading: false,
+                generation: store.generation + 1,
+              })
+            }
+          >
+            Complete navigation
+          </button>
          <button onClick={() => setStore("visible", (visible) => !visible)}>Toggle Review tab</button>
        </nav>
        <div style={{ width: "640px", height: "360px", border: "1px solid #555" }}>
@@ -57,3 +57,153 @@ story("hides the native view immediately while the pane stays mounted", async ({
  await toggle.click()
  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
 })
+
+story("shows the empty state over a blank native page and restores navigation", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Blank page", exact: true }).click()
+  await expect(root.getByText("Enter URL", { exact: true })).toBeVisible()
+  await expect(root.getByText('Or prompt "Open in the app browser"', { exact: true })).toBeVisible()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "false")
+  await expect(root.getByRole("button", { name: "Reload", exact: true })).toBeDisabled()
+
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("https://example.com/")
+  await expect(root.getByText("Enter URL", { exact: true })).toBeVisible()
+  await address.press("Enter")
+  await expect(address).not.toBeFocused()
+  await expect(root.getByText("Enter URL", { exact: true })).toBeHidden()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(root.getByRole("button", { name: "Reload", exact: true })).toBeEnabled()
+})
+
+story("keeps Stop available and hides the empty state while a blank page loads", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Loading page", exact: true }).click()
+  await expect(root.getByText("Enter URL", { exact: true })).toBeHidden()
+  await root.getByRole("button", { name: "Stop", exact: true }).click()
+  await expect(root.getByText("Enter URL", { exact: true })).toBeVisible()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "false")
+})
+
+story("keeps the submitted URL visible until the browser reports navigation", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Blank page", exact: true }).click()
+  await root.getByRole("button", { name: "Delay navigation", exact: true }).click()
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("https://example.com/")
+  await address.press("Enter")
+  await expect(address).not.toBeFocused()
+  await expect(address).toHaveValue("https://example.com/")
+  await expect(root.getByText("Enter URL", { exact: true })).toBeHidden()
+
+  await root.getByRole("button", { name: "Complete navigation", exact: true }).click()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(address).toHaveValue("https://example.com/")
+
+  await address.fill("https://unsubmitted.example/")
+  await root.getByRole("button", { name: "Delay navigation", exact: true }).click()
+  await expect(address).toHaveValue("https://example.com/")
+})
+
+story("restores the current URL when a submitted navigation is blocked", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Delay navigation", exact: true }).click()
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("https://blocked.example/")
+  await address.press("Enter")
+  await expect(address).toHaveValue("https://blocked.example/")
+  await root.getByRole("button", { name: "Block navigation", exact: true }).click()
+  await expect(root.getByText("ERR_BLOCKED_BY_CLIENT", { exact: true })).toBeVisible()
+  await expect(address).toHaveValue("https://alpha.example/")
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+})
+
+story("shows a themed failure state for only the failed tab and allows retry", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Failed page", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeVisible()
+  await expect(root.getByText("Check the URL and your connection, then try again.", { exact: true })).toBeVisible()
+  await expect(root.getByText("Request failed", { exact: true })).toBeHidden()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "false")
+  await expect(root.getByRole("textbox", { name: "Browser address", exact: true })).toHaveValue(
+    "https://alpha.example/",
+  )
+
+  await root.getByRole("button", { name: "Beta", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeHidden()
+  await expect(root.getByTestId("native-Beta")).toHaveAttribute("data-visible", "true")
+  await root.getByRole("button", { name: "Alpha", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeVisible()
+
+  await root.getByRole("button", { name: "Reload", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeHidden()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+})
+
+story("returns a failed tab to the empty state when an empty URL is submitted", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Failed page", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeVisible()
+  await root.getByRole("button", { name: "Delay navigation", exact: true }).click()
+
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("")
+  await address.press("Enter")
+  await expect(address).not.toBeFocused()
+  await expect(address).toHaveValue("")
+  await root.getByRole("button", { name: "Load current page", exact: true }).click()
+  await expect(root.getByRole("button", { name: "Stop", exact: true })).toBeEnabled()
+  await root.getByRole("button", { name: "Complete navigation", exact: true }).click()
+  await expect(root.getByText("URL can't be reached", { exact: true })).toBeHidden()
+  await expect(root.getByText("Enter URL", { exact: true })).toBeVisible()
+  await expect(root.getByRole("button", { name: "Reload", exact: true })).toBeDisabled()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "false")
+})
+
+story("selects the full URL when the address field gains focus", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.click()
+  await expect(address).toHaveJSProperty("selectionStart", 0)
+  await expect(address).toHaveJSProperty("selectionEnd", "https://alpha.example/".length)
+  await address.pressSequentially("https://example.com/")
+  await expect(address).toHaveValue("https://example.com/")
+  await address.press("Enter")
+  await expect(address).not.toBeFocused()
+  await address.focus()
+  await expect(address).toHaveJSProperty("selectionStart", 0)
+  await expect(address).toHaveJSProperty("selectionEnd", "https://example.com/".length)
+  await address.press("ArrowRight")
+  await address.click()
+  await expect(address).toHaveJSProperty("selectionStart", 0)
+  await expect(address).toHaveJSProperty("selectionEnd", "https://example.com/".length)
+})
+
+story("keeps the current page visible while a submitted URL loads", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  await root.getByRole("button", { name: "Delay navigation", exact: true }).click()
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("https://example.com/")
+  await address.press("Enter")
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(address).toHaveValue("https://example.com/")
+
+  await root.getByRole("button", { name: "Load current page", exact: true }).click()
+  await expect(root.getByRole("button", { name: "Stop", exact: true })).toBeEnabled()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await root.getByRole("button", { name: "Complete navigation", exact: true }).click()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(address).toHaveValue("https://example.com/")
+})
+
+story("keeps the current page and restores its URL when an empty address is submitted", async ({ page }) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  const address = root.getByRole("textbox", { name: "Browser address", exact: true })
+  await address.fill("")
+  await address.press("Enter")
+  await expect(address).not.toBeFocused()
+  await expect(address).toHaveValue("https://alpha.example/")
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(root.getByText("Enter URL", { exact: true })).toBeHidden()
+  await expect(root.getByRole("button", { name: "Reload", exact: true })).toBeEnabled()
+})
@@ -1,6 +1,6 @@
 {
  "name": "@opencode/app",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "description": "",
  "type": "module",
  "exports": {
@@ -10,8 +10,7 @@
    "./i18n/desktop-native": "./src/runtime/i18n/desktop-native.ts",
    "./updater": "./src/shell/updates/types.ts",
    "./wsl/types": "./src/servers/wsl/types.ts",
-    "./ssh": "./src/servers/ssh/types.ts",
-    "./ssh/schema": "./src/servers/ssh/schema.ts",
+    "./ssh": "./src/servers/ssh/types.ts",
    "./vite": "./vite.js",
    "./index.css": "./src/index.css"
  },
@@ -95,4 +94,3 @@
    "tailwindcss": "4.3.3"
  }
 }
-
@@ -3,19 +3,7 @@ import { checksum } from "@opencode/util/encode"
 import { SessionMessage } from "@opencode/schema/session-message"
 import { Skill } from "@opencode/schema/skill"
 import { Persistence } from "@/runtime/persistence/schema"
-// Effect twins of workspaces/files/types until this module moves to plain codecs.
-const SelectedLineRange = Persistence.struct({
-  start: Schema.Number,
-  end: Schema.Number,
-  side: Persistence.optional(Schema.Literals(["additions", "deletions"])),
-  endSide: Persistence.optional(Schema.Literals(["additions", "deletions"])),
-})
-const FileSelection = Persistence.struct({
-  startLine: Schema.Number,
-  startChar: Schema.Number,
-  endLine: Schema.Number,
-  endChar: Schema.Number,
-})
+import { FileSelection, SelectedLineRange } from "@/workspaces/files/types"

 const PartBase = {
  content: Schema.String,
@@ -240,5 +228,3 @@ export const PromptHistoryEntry = Schema.Union([HistoryEntry, HistoryPrompt]).pi
 export type PromptHistoryEntry = typeof PromptHistoryEntry.Type

 export const PromptHistoryState = Persistence.struct({ entries: Persistence.array(PromptHistoryEntry) })
-
-
@@ -11,15 +11,15 @@ import { Persist, persisted } from "@/runtime/persistence/storage"
 import { showToast } from "@/shell/notifications/toast"
 import { useDialog } from "@opencode/ui/context/dialog"
 import { createResource } from "solid-js"
-import { Codec } from "@/runtime/persistence/codec"
-
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"
 import type { HomeController } from "../model"
 import { useGlobal } from "@/runtime/server/runtime"
-
+import { SessionTransfer } from "@opencode/schema/session-transfer"
 import { useSshAuthenticate } from "@/servers/ssh/authenticate"

-export const HomeServersSchema = Codec.struct({
-  collapsed: Codec.lenientRecord(Codec.fallback(Codec.boolean, () => false)),
+export const HomeServersSchema = Schema.Struct({
+  collapsed: Persistence.record(Persistence.fallback(Schema.Boolean, () => false)),
 })

 export function createHomeProjectsController(home: HomeController) {
@@ -114,13 +114,8 @@ export function createHomeProjectsController(home: HomeController) {
              extensions: ["json"],
            },
            async (file) => {
-              // Validating an imported file is the one place the shared Effect schema is needed here.
-              const [{ Schema }, { SessionTransfer }] = await Promise.all([
-                import("effect"),
-                import("@opencode/schema/session-transfer"),
-              ])
-              const data = await Schema.decodeUnknownPromise(Schema.fromJsonString(SessionTransfer.Data))(
-                await file.text(),
+              const data = await Schema.decodeUnknownPromise(Schema.fromJsonString(SessionTransfer.Data))(
+                await file.text(),
              )
              const api = home.server.context(conn).sdk.api.session
              const imported = await api.import({
@@ -189,4 +184,3 @@ export function createHomeProjectsController(home: HomeController) {
 }

 export type HomeProjectsController = ReturnType<typeof createHomeProjectsController>
-
@@ -65,14 +65,14 @@
  }

  /* Keep the 1000px conversation intact, with 320px for the summary and its gutters.
-     Move only as far as needed; wider panels already have enough space in the margin. */
-  @container session-chat (min-width: 1320px) {
+     When they overlap, center the conversation in the space that remains beside the summary. */
+  @container session-chat (min-width: 1320px) and (width < 1640px) {
    [data-slot="session-chat-panel"][data-summary-open="true"]
      :is([data-timeline-virtual-content], [data-component="session-composer-dock"] > div) {
-      --session-summary-translate: min(0px, calc(50cqi - 820px));
+      --session-summary-translate: -160px;

      &:dir(rtl) {
-        --session-summary-translate: max(0px, calc(820px - 50cqi));
+        --session-summary-translate: 160px;
      }
    }
  }
@@ -5,7 +5,7 @@ import { Show, Suspense, createMemo, createSignal, lazy, onMount } from "solid-j
 import { createStore } from "solid-js/store"
 import { makeEventListener } from "@solid-primitives/event-listener"
 import { debounce } from "@solid-primitives/scheduled"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
 import createPresence from "solid-presence"
 import { Composer } from "@/composer/composer"
 import { ComposerDropzone } from "@/composer/dropzone"
@@ -21,6 +21,7 @@ import { useWorkspaceLocation } from "@/workspaces/location"
 import { useProviders } from "@/providers/catalog/providers"
 import { NEW_SESSION_CONTENT_WIDTH } from "@/new-session/layout"
 import { Persist, persisted } from "@/runtime/persistence/storage"
+import { Persistence } from "@/runtime/persistence/schema"
 import type { NewSessionWorkspaceController } from "./workspace/controller"
 import { NewSessionWordmark } from "./wordmark"
 import { SummaryPopover } from "@/session/summary/popover"
@@ -33,12 +34,12 @@ const NewSessionSummary = lazy(async () => {

 const providerTipDismissalDuration = 30 * 24 * 60 * 60 * 1000

-export const WorkspaceOnboardingSchema = Codec.struct({
-  used: Codec.boolean,
+export const WorkspaceOnboardingSchema = Persistence.struct({
+  used: Schema.Boolean,
 })

-export const ProviderTipSchema = Codec.struct({
-  dismissedAt: Codec.number,
+export const ProviderTipSchema = Persistence.struct({
+  dismissedAt: Schema.Finite,
 })

 export const WorkspaceTipSchema = ProviderTipSchema
@@ -266,4 +267,3 @@ function NewSessionTips(props: { workspaceEligible: boolean; onWorkspace: () =>
    </Show>
  )
 }
-
@@ -1,6 +1,7 @@
 import { useData } from "@/runtime/server/current"
 import { useServerSDK } from "@/runtime/server/client"
 import { normalizeProviderList } from "@/runtime/server/global-sync/utils"
+import { Iterable, pipe } from "effect"
 import { createEffect, createMemo, type Accessor } from "solid-js"
 import type { ProviderListResponse } from "@/runtime/server/types"
 import { useIntegrations } from "./integrations"
@@ -52,24 +53,34 @@ export function useProviders(directory: Accessor<string | undefined>) {
        .filter((integration) => popularProviderSet.has(integration.id))
        .map((integration) => ({ id: integration.id, name: integration.name }))
      const seen = new Set(catalog.map((integration) => integration.id))
-      const more = [...providers().all.values()]
-        .filter((p) => popularProviderSet.has(p.id) && !seen.has(p.id))
-        .map((p) => ({ id: p.id, name: p.name }))
-      return [...catalog, ...more]
+      return pipe(
+        providers().all,
+        Iterable.map(([, p]) => p),
+        Iterable.filter((p) => popularProviderSet.has(p.id) && !seen.has(p.id)),
+        Iterable.map((p) => ({ id: p.id, name: p.name })),
+        (v) => [...catalog, ...v],
+      )
    },
    connected: () => {
      const connected = new Set(providers().connected)
-      return [...providers().all.values()].filter((p) => connected.has(p.id))
+      return pipe(
+        providers().all,
+        Iterable.map(([, p]) => p),
+        Iterable.filter((p) => connected.has(p.id)),
+        (v) => Array.from(v),
+      )
    },
    paid: () => {
      const connected = new Set(providers().connected)
-      const paid = [...providers().all].filter(
-        ([id]) =>
-          connected.has(id) &&
-          (id !== "opencode" || Object.values(providers().all.get(id)?.models ?? {}).some((m) => m.cost?.input)),
-      )
+      const paid = [
+        ...Iterable.filter(
+          providers().all,
+          ([id]) =>
+            connected.has(id) &&
+            (id !== "opencode" || Object.values(providers().all.get(id)?.models ?? {}).some((m) => m.cost?.input)),
+        ),
+      ]
      return paid
    },
  }
 }
-
@@ -3,11 +3,12 @@ import { base64Encode } from "@opencode/util/encode"
 import { useParams } from "@solidjs/router"
 import { batch, createEffect, createMemo, onCleanup } from "solid-js"
 import { createStore } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema, SchemaGetter } from "effect"
 import { useModels } from "@/providers/models/models"
 import { useSettings } from "@/settings/model"
 import { useProviders } from "@/providers/catalog/providers"
 import { Persist, persisted } from "@/runtime/persistence/storage"
+import { Persistence } from "@/runtime/persistence/schema"
 import { hasCustomAgent, resolveAgent } from "./agent"
 import { cycleModelVariant, getConfiguredAgentVariant, resolveModelVariant } from "./variant"
 import { useWorkspaceLocation } from "@/workspaces/location"
@@ -17,45 +18,46 @@ import { useServerSDK } from "@/runtime/server/client"
 import { ScopedKey, type ServerScope } from "@/runtime/server/scope"
 import { useConfiguredModel } from "./configured"

-const ModelKeySchema = Codec.struct({
-  providerID: Codec.string,
-  modelID: Codec.string,
-  variant: Codec.optional(Codec.string),
+const ModelKeySchema = Schema.Struct({
+  providerID: Schema.String,
+  modelID: Schema.String,
+  variant: Schema.optional(Schema.String),
 })
 export type ModelKey = typeof ModelKeySchema.Type

-const ChoiceSchema = Codec.struct({
-  model: Codec.lenientOptional(ModelKeySchema),
-  variant: Codec.lenientOptional(Codec.nullOr(Codec.string)),
+const ChoiceSchema = Schema.Struct({
+  model: Persistence.optional(ModelKeySchema),
+  variant: Persistence.optional(Schema.NullOr(Schema.String)),
 })
-const StateSchema = Codec.struct({
+const StateSchema = Schema.Struct({
  ...ChoiceSchema.fields,
-  agent: Codec.lenientOptional(Codec.string),
-  choices: Codec.lenientOptional(Codec.record(ChoiceSchema)),
+  agent: Persistence.optional(Schema.String),
+  choices: Persistence.optional(Schema.Record(Schema.String, ChoiceSchema)),
 })
 type State = typeof StateSchema.Type

-const SessionsSchema = Codec.record(Codec.fallback(Codec.undefinedOr(StateSchema), () => undefined))
-
-const Current = Codec.struct({ session: SessionsSchema })
-const StoredSelection = Codec.struct(
-  {
-    session: Codec.lenientOptional(Codec.record(Codec.unknown)),
-    pick: Codec.lenientOptional(Codec.record(Codec.unknown)),
-  },
-  { preserve: true },
+const SessionsSchema = Schema.Record(
+  Schema.String,
+  Schema.mutableKey(Persistence.fallback(Schema.UndefinedOr(StateSchema), () => undefined)),
 )

-export const ModelSelectionSchema = Codec.migrate(
+const Current = Persistence.struct({ session: SessionsSchema })
+
+export const ModelSelectionSchema = Persistence.migrate(
  Current,
-  Codec.transform(StoredSelection, {
-    decode: (value) => ({
-      ...value,
-      session:
-        value.session ?? Object.fromEntries(Object.entries(value.pick ?? {}).filter(([key]) => key !== WORKSPACE_KEY)),
+  Schema.Struct({
+    session: Persistence.optional(Schema.Record(Schema.String, Schema.Unknown)),
+    pick: Persistence.optional(Schema.Record(Schema.String, Schema.Unknown)),
+  }).pipe(
+    Schema.decode({
+      decode: SchemaGetter.transform((value) => ({
+        session:
+          value.session ??
+          Object.fromEntries(Object.entries(value.pick ?? {}).filter(([key]) => key !== WORKSPACE_KEY)),
+      })),
+      encode: SchemaGetter.transform((value) => value),
    }),
-    encode: (value) => value,
-  }),
+  ),
 )

 const WORKSPACE_KEY = "__workspace__"
@@ -906,6 +906,10 @@ export const dict = {
  "session.browser.replaced": "Browser control moved to another desktop window.",
  "session.browser.suspended": "Browser suspended. Interact with this session to reconnect.",
  "session.browser.address.placeholder": "Enter URL",
+  "session.browser.empty.title": "Enter URL",
+  "session.browser.empty.description": 'Or prompt "Open in the app browser"',
+  "session.browser.failed.title": "URL can't be reached",
+  "session.browser.failed.description": "Check the URL and your connection, then try again.",

  "titlebar.update": "Update",
  "titlebar.tabs": "Tabs",
@@ -1,7 +1,7 @@
 import { flatten, resolveTemplate, translator, type Flatten } from "@solid-primitives/i18n"
 import { createEffect, createMemo, createResource, type JSX } from "solid-js"
 import { createStore } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
+import { Option, Schema, SchemaGetter } from "effect"
 import { createSimpleContext } from "@opencode/ui/context"
 import {
  I18nProvider,
@@ -12,6 +12,7 @@ import {
  type UiPluralCategory,
 } from "@opencode/ui/context/i18n"
 import { Persist, persisted } from "@/runtime/persistence/storage"
+import { Persistence } from "@/runtime/persistence/schema"
 import en from "@/runtime/i18n/en"
 import { dict } from "@opencode/ui/i18n/en"
 import {
@@ -55,9 +56,14 @@ function cookie(locale: Locale) {

 const LOCALES: readonly Locale[] = DESKTOP_NATIVE_LOCALES

-const LocaleSchema = Codec.literals(DESKTOP_NATIVE_LOCALES)
-const StoredLocaleSchema = Codec.struct({
-  locale: Codec.transform(Codec.string, { decode: normalizeLocale, encode: (locale) => locale }),
+const LocaleSchema = Schema.Literals(DESKTOP_NATIVE_LOCALES)
+const StoredLocaleSchema = Schema.Struct({
+  locale: Schema.String.pipe(
+    Schema.decodeTo(LocaleSchema, {
+      decode: SchemaGetter.transform(normalizeLocale),
+      encode: SchemaGetter.transform((locale) => locale),
+    }),
+  ),
 })

 const INTL = DESKTOP_NATIVE_LOCALE_TAGS
@@ -154,11 +160,11 @@ function detectLocale(): Locale {
 }

 export function normalizeLocale(value: string): Locale {
-  return Codec.decodeOption(LocaleSchema, value) ?? "en"
+  return Option.getOrElse(Schema.decodeUnknownOption(LocaleSchema)(value), () => "en")
 }

-export const languageSchema = Codec.struct({
-  locale: StoredLocaleSchema.fields.locale,
+export const languageSchema = Persistence.struct({
+  locale: StoredLocaleSchema.fields.locale,
 })

 function readStoredLocale() {
@@ -166,7 +172,9 @@ function readStoredLocale() {
  try {
    const raw = localStorage.getItem("opencode.global.dat:language")
    if (!raw) return
-    return Codec.decodeOption(Codec.fromJsonString(StoredLocaleSchema), raw)?.locale
+    const next = Schema.decodeUnknownOption(Schema.fromJsonString(StoredLocaleSchema))(raw)
+    if (Option.isNone(next)) return
+    return next.value.locale
  } catch {
    return
  }
@@ -288,4 +296,3 @@ export function UiI18nBridge(props: { children?: JSX.Element }) {
    </I18nProvider>
  )
 }
-
@@ -1,17 +0,0 @@
-import { expect, test } from "bun:test"
-import { Codec } from "./codec"
-
-// Type-level checks: these compile only if inference matches what `typeof schema.Type` gave callers.
-test("struct types infer optional and required fields", () => {
-  const s = Codec.struct({ id: Codec.string, tab: Codec.optional(Codec.string), n: Codec.lenientOptional(Codec.number) })
-  const value: typeof s.Type = { id: "x" }
-  const tab: string | undefined = value.tab
-  const n: number | undefined = value.n
-  const t = Codec.transform(s, { decode: (old) => old.tab ?? old.id, encode: (v) => ({ id: v }) })
-  const out: string | Codec.Invalid = t.decode({ id: "a" })
-  const onlyOptional = Codec.struct({ tab: Codec.optional(Codec.string) })
-  const empty: typeof onlyOptional.Type = {}
-  const maybe: string | undefined = empty.tab
-  const viaTransform = Codec.transform(onlyOptional, { decode: (old) => old.tab, encode: (tab) => ({ tab }) })
-  expect([tab, n, out, maybe, viaTransform.decode({})]).toEqual([undefined, undefined, "a", undefined, undefined])
-})
@@ -1,85 +0,0 @@
-import { describe, expect, test } from "bun:test"
-import { Codec } from "./codec"
-
-describe("Codec", () => {
-  test("primitives reject the wrong shape and finite numbers only", () => {
-    expect(Codec.string.decode("a")).toBe("a")
-    expect(Codec.string.decode(1)).toBe(Codec.INVALID)
-    expect(Codec.number.decode(1.5)).toBe(1.5)
-    expect(Codec.number.decode(Number.NaN)).toBe(Codec.INVALID)
-    expect(Codec.nonNegativeInt.decode(-1)).toBe(Codec.INVALID)
-    expect(Codec.literals(["a", "b"]).decode("c")).toBe(Codec.INVALID)
-    expect(Codec.literal("x").decode("x")).toBe("x")
-  })
-
-  test("struct keeps optional fields absent and rejects invalid required ones", () => {
-    const codec = Codec.struct({ id: Codec.string, title: Codec.optional(Codec.string), n: Codec.lenientOptional(Codec.number) })
-    expect(codec.decode({ id: "1" })).toEqual({ id: "1" })
-    expect(codec.decode({ id: "1", title: "t", n: "bad" })).toEqual({ id: "1", title: "t" })
-    expect(codec.decode({ id: "1", title: 3 })).toBe(Codec.INVALID)
-    expect(codec.decode({ title: "t" })).toBe(Codec.INVALID)
-    expect(codec.decode([])).toBe(Codec.INVALID)
-    expect(codec.encode({ id: "1" })).toEqual({ id: "1" })
-    const value: typeof codec.Type = { id: "1", title: undefined }
-    expect(value.id).toBe("1")
-  })
-
-  test("lenient collections recover what they can", () => {
-    const items = Codec.lenientArray(Codec.struct({ id: Codec.string }))
-    expect(items.decode([{ id: "a" }, { id: 1 }, "x", { id: "b" }])).toEqual([{ id: "a" }, { id: "b" }])
-    expect(items.decode("nope")).toEqual([])
-    expect(Codec.array(Codec.string).decode(["a", 1])).toBe(Codec.INVALID)
-    const map = Codec.lenientRecord(Codec.boolean)
-    expect(map.decode({ a: true, b: "x" })).toEqual({})
-    expect(map.decode({ a: true })).toEqual({ a: true })
-  })
-
-  test("union, transform and fallback compose", () => {
-    const session = Codec.struct({ type: Codec.literal("session"), id: Codec.string })
-    const draft = Codec.struct({ type: Codec.literal("draft"), directory: Codec.string })
-    const tab = Codec.union([session, draft])
-    expect(tab.decode({ type: "draft", directory: "/x" })).toEqual({ type: "draft", directory: "/x" })
-    expect(tab.decode({ type: "other" })).toBe(Codec.INVALID)
-    const upper = Codec.transform(Codec.string, { decode: (s) => s.toUpperCase(), encode: (s) => s.toLowerCase() })
-    expect(upper.decode("ab")).toBe("AB")
-    expect(upper.encode("AB")).toBe("ab")
-    const safe = Codec.fallback(Codec.number, () => 7)
-    expect(safe.decode("x")).toBe(7)
-    expect(safe.decode(undefined)).toBe(7)
-    expect(safe.decode(2)).toBe(2)
-  })
-
-  test("brand constructs and decodes as its base", () => {
-    const Key = Codec.brand<"ServerConnection.Key">()
-    const key = Key.make("http://a")
-    expect(Key.decode(key)).toBe(key)
-    expect(Key.decode(3)).toBe(Codec.INVALID)
-  })
-
-  test("withInitial recovers field by field and merges new defaults", () => {
-    const layout = Codec.struct({
-      sidebar: Codec.struct({ opened: Codec.boolean, width: Codec.number }),
-      theme: Codec.lenientOptional(Codec.literals(["light", "dark"])),
-    })
-    const initial: typeof layout.Type = { sidebar: { opened: true, width: 240 } }
-    const codec = Codec.fromJsonString(Codec.withInitial(layout, initial))
-    expect(codec.decode(JSON.stringify({ sidebar: { opened: false, width: "wide" }, theme: "dark" }))).toEqual({
-      sidebar: { opened: false, width: 240 },
-      theme: "dark",
-    })
-    expect(codec.decode(JSON.stringify({ sidebar: 5 }))).toEqual(initial)
-    expect(codec.decode("{not json")).toBe(Codec.INVALID)
-    expect(JSON.parse(codec.encode({ sidebar: { opened: true, width: 1 } }))).toEqual({ sidebar: { opened: true, width: 1 } })
-  })
-
-  test("migrate reads the old shape first", () => {
-    const current = Codec.struct({ tabs: Codec.array(Codec.string) })
-    const previous = Codec.struct({ tab: Codec.optional(Codec.string) })
-    const read = Codec.transform(previous, {
-      decode: (old) => ({ tabs: old.tab ? [old.tab] : [] }),
-      encode: (value) => ({ tab: value.tabs[0] }),
-    })
-    const codec = Codec.withInitial(Codec.migrate(current, read), { tabs: [] })
-    expect(codec.decode({ tab: "a" })).toEqual({ tabs: ["a"] })
-  })
-})
@@ -1,366 +0,0 @@
-export * as Codec from "./codec"
-
-// Plain codecs for persisted state. They replace Effect Schema in the renderer's initial module
-// graph, where Effect's own module initialisation was the single largest startup cost that was not
-// rendering. Semantics mirror the Persistence helpers: decoding never throws, `INVALID` marks a
-// value that cannot be recovered, and the lenient combinators recover what they can.
-
-export const INVALID: unique symbol = Symbol.for("opencode/persistence/codec/invalid")
-export type Invalid = typeof INVALID
-
-const tag: unique symbol = Symbol.for("opencode/persistence/codec")
-
-export interface Of<T, E = unknown> {
-  readonly [tag]: true
-  /** Phantom: `typeof codec.Type` is the decoded type, as with Effect schemas. */
-  readonly Type: T
-  readonly Encoded: E
-  readonly optional?: boolean
-  decode(input: unknown): T | Invalid
-  encode(value: T): E
-}
-
-export type Any = Of<any, any>
-export type Type<C extends Any> = C["Type"]
-
-export function isCodec(value: unknown): value is Any {
-  return typeof value === "object" && value !== null && tag in value
-}
-
-export function make<T, E = unknown>(decode: (input: unknown) => T | Invalid, encode: (value: T) => E): Of<T, E> {
-  return { [tag]: true, decode, encode } as Of<T, E>
-}
-
-export function is<T>(codec: Of<T>, input: unknown): input is T {
-  return codec.decode(input) !== INVALID
-}
-
-export function decodeOption<T>(codec: Of<T>, input: unknown): T | undefined {
-  const value = codec.decode(input)
-  return value === INVALID ? undefined : value
-}
-
-export function decodeOrThrow<T>(codec: Of<T>, input: unknown): T {
-  const value = codec.decode(input)
-  if (value === INVALID) throw new Error("Value does not match its codec")
-  return value
-}
-
-/** Encodes and checks the result decodes, so an invalid in-memory value fails loudly instead of persisting. */
-export function encodeOrThrow<T, E>(codec: Of<T, E>, value: T): E {
-  const encoded = codec.encode(value)
-  if (codec.decode(encoded) === INVALID) throw new Error("Value does not match its codec")
-  return encoded
-}
-
-const identity = <T>(value: T) => value
-
-export const string: Of<string, string> = make((v) => (typeof v === "string" ? v : INVALID), identity)
-export const boolean: Of<boolean, boolean> = make((v) => (typeof v === "boolean" ? v : INVALID), identity)
-export const unknown: Of<unknown, unknown> = make((v) => v, identity)
-/** Finite numbers only: NaN and infinities are not JSON and never valid state. */
-export const number: Of<number, number> = make((v) => (typeof v === "number" && Number.isFinite(v) ? v : INVALID), identity)
-export const int: Of<number, number> = make((v) => (typeof v === "number" && Number.isInteger(v) ? v : INVALID), identity)
-export const nonNegativeInt: Of<number, number> = make(
-  (v) => (typeof v === "number" && Number.isInteger(v) && v >= 0 ? v : INVALID),
-  identity,
-)
-
-export function literal<const L extends string | number | boolean | null>(value: L): Of<L, L> {
-  return make((v) => (v === value ? value : INVALID), identity)
-}
-
-export function literals<const L extends ReadonlyArray<string | number | boolean | null>>(values: L): Of<L[number], L[number]> {
-  const set = new Set<unknown>(values)
-  return make((v) => (set.has(v) ? (v as L[number]) : INVALID), identity)
-}
-
-/** A string carrying a nominal brand, with the constructor Effect's `Schema.brand` gave callers. */
-export function brand<B extends string>(): Of<string & { readonly [K in B]: B }, string> & {
-  make(value: string): string & { readonly [K in B]: B }
-} {
-  return Object.assign(make<string & { readonly [K in B]: B }, string>((v) => (typeof v === "string" ? (v as never) : INVALID), identity), {
-    make: (value: string) => value as never,
-  })
-}
-
-export function nullOr<T, E>(codec: Of<T, E>): Of<T | null, E | null> {
-  return make((v) => (v === null ? null : codec.decode(v)), (v) => (v === null ? null : codec.encode(v)))
-}
-
-export function undefinedOr<T, E>(codec: Of<T, E>): Of<T | undefined, E | undefined> {
-  return make((v) => (v === undefined ? undefined : codec.decode(v)), (v) => (v === undefined ? undefined : codec.encode(v)))
-}
-
-/** A struct field that may be absent. Present but invalid values make the struct invalid. */
-export function optional<T, E>(codec: Of<T, E>): Of<T | undefined, E | undefined> & { readonly optional: true } {
-  return { ...undefinedOr(codec), optional: true } as never
-}
-
-/** A struct field that may be absent, and whose invalid values are dropped rather than rejected. */
-export function lenientOptional<T, E>(codec: Of<T, E>): Of<T | undefined, E | undefined> & { readonly optional: true } {
-  return {
-    ...make<T | undefined, E | undefined>(
-      (v) => {
-        if (v === undefined) return undefined
-        const value = codec.decode(v)
-        return value === INVALID ? undefined : value
-      },
-      (v) => (v === undefined ? undefined : codec.encode(v)),
-    ),
-    optional: true,
-  } as never
-}
-
-type Fields = Record<string, Any>
-type OptionalKeys<F extends Fields> = { [K in keyof F]: F[K] extends { optional: true } ? K : never }[keyof F]
-type RequiredKeys<F extends Fields> = Exclude<keyof F, OptionalKeys<F>>
-type Simplify<T> = { [K in keyof T]: T[K] } & {}
-export type StructType<F extends Fields> = Simplify<
-  { [K in RequiredKeys<F>]: F[K]["Type"] } & { [K in OptionalKeys<F>]?: F[K]["Type"] }
->
-export type StructEncoded<F extends Fields> = Simplify<
-  { [K in RequiredKeys<F>]: F[K]["Encoded"] } & { [K in OptionalKeys<F>]?: F[K]["Encoded"] }
->
-
-export interface Struct<F extends Fields> extends Of<StructType<F>, StructEncoded<F>> {
-  readonly fields: F
-}
-
-// `preserve` keeps keys the struct does not declare, for migration shapes that only describe the
-// fields they rewrite (Effect's `onExcessProperty: "preserve"`); the current schema then decides.
-export function struct<const F extends Fields>(fields: F, options?: { preserve?: boolean }): Struct<F> {
-  const entries = Object.entries(fields)
-  return {
-    ...make<StructType<F>, StructEncoded<F>>(
-      (input) => {
-        if (typeof input !== "object" || input === null || Array.isArray(input)) return INVALID
-        const record = input as Record<string, unknown>
-        const out: Record<string, unknown> = options?.preserve ? { ...record } : {}
-        for (const [key, codec] of entries) {
-          const present = Object.hasOwn(record, key)
-          if (!present && codec.optional) continue
-          const value = codec.decode(record[key])
-          if (value === INVALID) return INVALID
-          if (value !== undefined || present) out[key] = value
-          else delete out[key]
-        }
-        return out as StructType<F>
-      },
-      (value) => {
-        const out: Record<string, unknown> = {}
-        for (const [key, codec] of entries) {
-          const field = (value as Record<string, unknown>)[key]
-          if (field === undefined && !Object.hasOwn(value as object, key)) continue
-          out[key] = codec.encode(field)
-        }
-        return out as StructEncoded<F>
-      },
-    ),
-    fields,
-  }
-}
-
-export function array<T, E>(codec: Of<T, E>): Of<T[], E[]> {
-  return make(
-    (input) => {
-      if (!Array.isArray(input)) return INVALID
-      const out: T[] = []
-      for (const item of input) {
-        const value = codec.decode(item)
-        if (value === INVALID) return INVALID
-        out.push(value)
-      }
-      return out
-    },
-    (value) => value.map((item) => codec.encode(item)),
-  )
-}
-
-/** Keeps the items that decode and drops the rest, like `Persistence.array`. */
-export function lenientArray<T, E>(codec: Of<T, E>): Of<T[], E[]> {
-  return make(
-    (input) => {
-      if (!Array.isArray(input)) return []
-      return input.flatMap((item) => {
-        const value = codec.decode(item)
-        return value === INVALID ? [] : [value]
-      })
-    },
-    (value) => value.map((item) => codec.encode(item)),
-  )
-}
-
-export function record<T, E>(codec: Of<T, E>): Of<Record<string, T>, Record<string, E>> {
-  return make(
-    (input) => {
-      if (typeof input !== "object" || input === null || Array.isArray(input)) return INVALID
-      const out: Record<string, T> = {}
-      for (const [key, item] of Object.entries(input)) {
-        const value = codec.decode(item)
-        if (value === INVALID) return INVALID
-        out[key] = value
-      }
-      return out
-    },
-    (value) => Object.fromEntries(Object.entries(value).map(([key, item]) => [key, codec.encode(item)])),
-  )
-}
-
-/** A record that drops entries whose values are invalid, the replacement for `catchDecoding` to none. */
-export function sparseRecord<T, E>(codec: Of<T, E>): Of<Record<string, T>, Record<string, E>> {
-  return make(
-    (input) => {
-      if (typeof input !== "object" || input === null || Array.isArray(input)) return INVALID
-      const out: Record<string, T> = {}
-      for (const [key, item] of Object.entries(input)) {
-        const value = codec.decode(item)
-        if (value !== INVALID) out[key] = value
-      }
-      return out
-    },
-    (value) => Object.fromEntries(Object.entries(value).map(([key, item]) => [key, codec.encode(item)])),
-  )
-}
-
-/** An invalid record becomes empty rather than failing the whole store, like `Persistence.record`. */
-export function lenientRecord<T, E>(codec: Of<T, E>): Of<Record<string, T>, Record<string, E>> {
-  const strict = record(codec)
-  return make(
-    (input) => {
-      const value = strict.decode(input)
-      return value === INVALID ? {} : value
-    },
-    strict.encode,
-  )
-}
-
-export function union<const C extends ReadonlyArray<Any>>(codecs: C): Of<C[number]["Type"], C[number]["Encoded"]> {
-  return make(
-    (input) => {
-      for (const codec of codecs) {
-        const value = codec.decode(input)
-        if (value !== INVALID) return value
-      }
-      return INVALID
-    },
-    (value) => {
-      // Encode with the first member that accepts the value's shape; members are disjoint in practice.
-      for (const codec of codecs) if (codec.decode(value) !== INVALID) return codec.encode(value)
-      return value as C[number]["Encoded"]
-    },
-  )
-}
-
-/** Maps a decoded value into another shape, the replacement for `decodeTo` + `SchemaGetter.transform`. */
-export function transform<T, E, T2>(
-  codec: Of<T, E>,
-  options: { decode: (value: T) => T2; encode: (value: T2) => T },
-): Of<T2, E> {
-  return make(
-    (input) => {
-      const value = codec.decode(input)
-      return value === INVALID ? INVALID : options.decode(value)
-    },
-    (value) => codec.encode(options.encode(value)),
-  )
-}
-
-/** Decodes with `source`, maps, then validates with `target`: Effect's `decodeTo` with a transform. */
-export function decodeTo<T, E, T2, E2>(
-  source: Of<T, E>,
-  target: Of<T2, E2>,
-  options: { decode: (value: T) => E2; encode: (value: T2) => T },
-): Of<T2, E> {
-  return make(
-    (input) => {
-      const value = source.decode(input)
-      return value === INVALID ? INVALID : target.decode(options.decode(value))
-    },
-    (value) => source.encode(options.encode(value)),
-  )
-}
-
-/** Invalid and missing values become `value()`, like `Persistence.fallback`. */
-export function fallback<T, E>(codec: Of<T, E>, value: () => NoInfer<T>): Of<T, E> {
-  return make(
-    (input) => {
-      if (input === undefined) return value()
-      const decoded = codec.decode(input)
-      return decoded === INVALID ? value() : decoded
-    },
-    codec.encode,
-  )
-}
-
-export function fromJsonString<T, E>(codec: Of<T, E>): Of<T, string> {
-  return make(
-    (input) => {
-      if (typeof input !== "string") return INVALID
-      try {
-        return codec.decode(JSON.parse(input))
-      } catch {
-        return INVALID
-      }
-    },
-    (value) => JSON.stringify(codec.encode(value)),
-  )
-}
-
-export type Decoder = Pick<Of<unknown>, "decode">
-export type Migrated<C extends Any> = { readonly current: C; readonly read: Decoder }
-
-/** Older stored shapes go through `read` first; `current` describes what the store holds today. */
-export function migrate<C extends Any>(current: C, read: Decoder): Migrated<C> {
-  return { current, read }
-}
-
-function isMigrated<C extends Any>(definition: C | Migrated<C>): definition is Migrated<C> {
-  return !isCodec(definition) && "current" in definition
-}
-
-// Stored values recover field by field against the initial value: an object's valid fields are
-// kept, invalid or missing ones take their initial counterpart, and the result is merged over the
-// initial so new fields appear with their defaults. Mirrors `Persistence.withInitial`.
-export function withInitial<C extends Any>(definition: C | Migrated<C>, initial: Type<C>): Of<Type<C>, unknown> {
-  const codec = isMigrated(definition) ? definition.current : definition
-  const read = isMigrated(definition) ? definition.read : unknown
-  return make(
-    (input) => {
-      const stored = read.decode(input)
-      if (stored === INVALID) return INVALID
-      return merge(initial, recover(codec, stored, initial))
-    },
-    (value) => codec.encode(value),
-  )
-}
-
-function recover(codec: Any, value: unknown, initial: unknown): unknown {
-  if (value === undefined) return initial
-  if ("fields" in codec && isObject(value)) {
-    const fields = (codec as Struct<Fields>).fields
-    return Object.fromEntries(
-      Object.entries(fields).flatMap(([name, field]) => {
-        const defaults = isObject(initial) ? initial[name] : undefined
-        const next = recover(field, value[name], defaults)
-        if (next === undefined && !Object.hasOwn(value, name) && defaults === undefined) return []
-        return [[name, next]]
-      }),
-    )
-  }
-  const decoded = codec.decode(value)
-  return decoded === INVALID ? initial : decoded
-}
-
-function merge(initial: unknown, value: unknown): unknown {
-  if (value === undefined) return initial
-  if (!isObject(initial) || !isObject(value)) return value
-  return Object.fromEntries(
-    [...new Set([...Object.keys(initial), ...Object.keys(value)])].map((key) => [key, merge(initial[key], value[key])]),
-  )
-}
-
-function isObject(value: unknown): value is Record<string, unknown> {
-  return typeof value === "object" && value !== null && !Array.isArray(value)
-}
-
@@ -3,7 +3,6 @@ import { Schema } from "effect"
 import { WorkspaceOnboardingSchema, ProviderTipSchema, WorkspaceTipSchema } from "@/new-session/view"
 import { ModelSelectionSchema } from "@/providers/models/selection"
 import { Persistence } from "@/runtime/persistence/schema"
-import { Codec } from "@/runtime/persistence/codec"
 import { FileViewsSchema } from "@/workspaces/files/view-cache"
 import { languageSchema } from "@/runtime/i18n/language"
 import { HomeServersSchema } from "@/home/projects/controller"
@@ -11,9 +10,9 @@ import { ModelProvidersSchema } from "@/settings/models/models"

 describe("persisted consumer schemas", () => {
  test("onboarding and provider tip retain defaults and validate stored values", () => {
-    const onboarding = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(WorkspaceOnboardingSchema, { used: false }), input))
-    const tip = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(ProviderTipSchema, { dismissedAt: 0 }), input))
-    const workspaceTip = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(WorkspaceTipSchema, { dismissedAt: 0 }), input))
+    const onboarding = Schema.decodeUnknownSync(Persistence.withInitial(WorkspaceOnboardingSchema, { used: false }))
+    const tip = Schema.decodeUnknownSync(Persistence.withInitial(ProviderTipSchema, { dismissedAt: 0 }))
+    const workspaceTip = Schema.decodeUnknownSync(Persistence.withInitial(WorkspaceTipSchema, { dismissedAt: 0 }))
    expect(onboarding({})).toEqual({ used: false })
    expect(onboarding({ used: "true" })).toEqual({ used: false })
    expect(onboarding({ used: true })).toEqual({ used: true })
@@ -26,7 +25,7 @@ describe("persisted consumer schemas", () => {

  test("collapse records recover malformed entries without losing valid siblings", () => {
    for (const schema of [HomeServersSchema, ModelProvidersSchema]) {
-      const decode = (input: unknown) => Codec.decodeOrThrow(Codec.withInitial(schema, { collapsed: {} }), input)
+      const decode = Schema.decodeUnknownSync(Persistence.withInitial(schema, { collapsed: {} }))
      expect(decode({})).toEqual({ collapsed: {} })
      expect(decode({ collapsed: [] })).toEqual({ collapsed: {} })
      expect(decode({ collapsed: { open: false, closed: true, invalid: "false" } })).toEqual({
@@ -36,19 +35,21 @@ describe("persisted consumer schemas", () => {
  })

  test("model selection migrates legacy picks and omits workspace state", () => {
-    const decode = (input: unknown) => Codec.decodeOrThrow(Codec.withInitial(ModelSelectionSchema, { session: {} }), input)
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(ModelSelectionSchema, { session: {} }))
    expect(decode({})).toEqual({ session: {} })
    const state = decode({ pick: { __workspace__: { agent: "plan" }, session1: { agent: "build" } } })
    expect(state.session.session1?.agent).toBe("build")
    expect(state.session.__workspace__).toBeUndefined()
-    const encoded = Codec.fromJsonString(Codec.withInitial(ModelSelectionSchema, { session: {} })).encode(state)
+    const encoded = Schema.encodeSync(
+      Schema.fromJsonString(Persistence.withInitial(ModelSelectionSchema, { session: {} })),
+    )(state)
    expect(JSON.parse(encoded)).toEqual({ session: { session1: { agent: "build" } } })
    expect(decode(JSON.parse(encoded))).toEqual(state)
  })

  test("current model selections take precedence over legacy picks", () => {
    expect(
-      Codec.decodeOrThrow(Codec.withInitial(ModelSelectionSchema, { session: {} }), {
+      Schema.decodeUnknownSync(Persistence.withInitial(ModelSelectionSchema, { session: {} }))({
        session: {},
        pick: { session1: { agent: "plan" } },
      }),
@@ -56,7 +57,7 @@ describe("persisted consumer schemas", () => {
  })

  test("model selection validates nested model keys and preserves explicit null variants", () => {
-    const state = Codec.decodeOrThrow(Codec.withInitial(ModelSelectionSchema, { session: {} }), {
+    const state = Schema.decodeUnknownSync(Persistence.withInitial(ModelSelectionSchema, { session: {} }))({
      session: {
        good: { agent: "build", model: { providerID: "provider", modelID: "model", variant: "high" }, variant: null },
        partial: { agent: "plan", model: { providerID: "provider", modelID: 42 }, variant: false },
@@ -75,7 +76,7 @@ describe("persisted consumer schemas", () => {
  })

  test("file views validate scroll positions and line sides independently", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(FileViewsSchema, { file: {} }), input))
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(FileViewsSchema, { file: {} }))
    expect(decode({})).toEqual({ file: {} })
    const state = decode({
      file: {
@@ -102,7 +103,7 @@ describe("persisted consumer schemas", () => {
  })

  test("language preserves runtime defaults and normalizes unsupported locales to English", () => {
-    const decode = (input: unknown) => Codec.decodeOrThrow(Codec.withInitial(languageSchema, { locale: "fr" }), input)
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(languageSchema, { locale: "fr" }))
    expect(decode({})).toEqual({ locale: "fr" })
    expect(decode({ locale: undefined })).toEqual({ locale: "fr" })
    expect(decode({ locale: 42 })).toEqual({ locale: "fr" })
@@ -110,6 +111,3 @@ describe("persisted consumer schemas", () => {
    expect(decode({ locale: "ar" })).toEqual({ locale: "ar" })
  })
 })
-
-
-
@@ -1,5 +1,5 @@
 import type { AsyncStorage } from "@solid-primitives/storage"
-import { Codec } from "./codec"
+import { Option, Schema } from "effect"

 export type BlobReference = { id: string; url: string }

@@ -312,12 +312,12 @@ export function createDraftStore(driver: Driver, options: { grace?: number } = {
    getItem: async (key) => {
      const value = await driver.get(key)
      if (value === null) return null
-      const parsed = Codec.fromJsonString(Codec.unknown).decode(value)
-      // Let the owning persistence codec apply its invalid-document policy.
-      if (parsed === Codec.INVALID) return value
-      // A loaded document is live in the composer: pin its images before decode mints their URLs.
-      retain(key, imageIDs(parsed), grace)
-      return JSON.stringify(await decode(parsed))
+      const parsed = Schema.decodeUnknownOption(Schema.fromJsonString(Schema.Unknown))(value)
+      // Let the owning persistence codec apply its invalid-document policy.
+      if (Option.isNone(parsed)) return value
+      // A loaded document is live in the composer: pin its images before decode mints their URLs.
+      retain(key, imageIDs(parsed.value), grace)
+      return JSON.stringify(await decode(parsed.value))
    },
    setItem: (key, value) => setDocument(key, JSON.parse(value)),
    setDocument,
@@ -455,4 +455,3 @@ export async function blobDataUrl(blob: BlobReference, mime: string) {
 export function createLegacyBlobReference(dataUrl: string): BlobReference {
  return { id: dataUrl, url: dataUrl }
 }
-
@@ -6,7 +6,6 @@ import { createStore, type SetStoreFunction, type Store } from "solid-js/store"
 import { Option, Schema } from "effect"
 import { pathKey } from "@/workspaces/path-key"
 import { ScopedKey, ServerScope } from "@/runtime/server/scope"
-import { Codec } from "./codec"
 import { persistStore } from "./persist"
 import { Persistence } from "./schema"

@@ -473,57 +472,25 @@ export function removePersisted(
  }
 }

-type Definition<S extends Schema.ConstraintCodec<object, unknown> | Codec.Any> =
-  | S
-  | Persistence.Migrated<Extract<S, Schema.ConstraintCodec<object, unknown>>>
-  | Codec.Migrated<Extract<S, Codec.Any>>
-
-// Persisted stores are moving from Effect Schema to the plain codecs in ./codec so the renderer
-// stops paying for Effect at startup; both are accepted while the migration is underway.
-function serializer<S extends Schema.ConstraintCodec<object, unknown> | Codec.Any>(
-  definition: Definition<S>,
-  initial: S["Type"],
-) {
-  if (Codec.isCodec(definition) || (!("current" in definition) ? false : Codec.isCodec(definition.current))) {
-    const codec = Codec.withInitial(definition as Codec.Any | Codec.Migrated<Codec.Any>, initial)
-    const json = Codec.fromJsonString(codec)
-    return {
-      decode: (raw: string) => Codec.decodeOption(json, raw) as S["Type"] | undefined,
-      deserialize: (raw: unknown) => Codec.decodeOrThrow(json, raw) as S["Type"],
-      serialize: (value: S["Type"]) => Codec.encodeOrThrow(json, value),
-      encode: (value: S["Type"]) => Codec.encodeOrThrow(codec, value),
-      initial: Codec.decodeOrThrow(codec, codec.encode(initial)) as S["Type"],
-    }
-  }
-  const schema = definition as Schema.ConstraintCodec<object, unknown> | Persistence.Migrated<Schema.ConstraintCodec<object, unknown>>
-  const initialized = Persistence.withInitial(schema, initial as object)
-  const json = Schema.fromJsonString(initialized)
-  const decode = Schema.decodeUnknownOption(json)
-  return {
-    decode: (raw: string) => Option.getOrUndefined(decode(raw)) as S["Type"] | undefined,
-    deserialize: Schema.decodeUnknownSync(json) as (raw: unknown) => S["Type"],
-    serialize: Schema.encodeSync(json) as (value: S["Type"]) => string,
-    encode: Schema.encodeSync(initialized) as (value: S["Type"]) => unknown,
-    initial: Schema.decodeUnknownSync(Schema.toType(initialized))(initial as object) as S["Type"],
-  }
-}
-
-export function persisted<S extends Schema.ConstraintCodec<object, unknown> | Codec.Any>(
+export function persisted<S extends Schema.ConstraintCodec<object, unknown>>(
  target: string | PersistTarget,
-  schema: Definition<S>,
+  schema: S | Persistence.Migrated<S>,
  initial: NoInfer<S["Type"]>,
  platformOverride?: Platform,
 ): PersistedWithReady<S["Type"]> {
  const platform = platformOverride ?? usePlatform()
  const config = resolveTarget(typeof target === "string" ? { key: target } : target, platform)

-  const codec = serializer<S>(schema, initial)
-  const { encode, serialize } = codec
+  const initialized = Persistence.withInitial(schema, initial)
+  const json = Schema.fromJsonString(initialized)
+  const decode = Schema.decodeUnknownOption(json)
+  const encode = Schema.encodeSync(initialized)
+  const serialize = Schema.encodeSync(json)
  const normalize = (raw: string) => {
-    const value = codec.decode(raw)
-    if (value !== undefined) return serialize(value)
+    const value = decode(raw)
+    if (Option.isSome(value)) return serialize(value.value)
  }
-  const store = createStore<S["Type"]>(codec.initial)
+  const store = createStore<S["Type"]>(Schema.decodeUnknownSync(Schema.toType(initialized))(initial))
  const isDesktop = platform.platform === "desktop" && !!platform.storage
  const draft = config.draft ? platform.draftStore : undefined
  const prefix = `${config.storage ?? "default"}:`
@@ -635,7 +602,7 @@ export function persisted<S extends Schema.ConstraintCodec<object, unknown> | Co
    name: config.key,
    storage,
    serialize,
-    deserialize: codec.deserialize,
+    deserialize: Schema.decodeUnknownSync(json),
    sync: channel ? messageSync(channel) : undefined,
    // Drafts take the encoded document itself so large text is externalized without the store
    // re-parsing the serialized form on every save.
@@ -1,11 +0,0 @@
-import type { Brand } from "effect"
-import { Codec } from "@/runtime/persistence/codec"
-
-// The server key's brand is shared with the Effect schema in ./persistence.ts (type only, so this
-// module loads nothing of Effect), letting stores port to plain codecs one at a time.
-export type ServerKey = string & Brand.Brand<"ServerConnection.Key">
-
-export const ServerKey: Codec.Of<ServerKey, string> & { make(value: string): ServerKey } = Object.assign(
-  Codec.make<ServerKey, string>((v) => (typeof v === "string" ? (v as ServerKey) : Codec.INVALID), (v) => v),
-  { make: (value: string) => value as ServerKey },
-)
@@ -1,14 +1,15 @@
 import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
 import { IconState, ModelState, ProjectState, VcsState, serverState } from "./persistence"
 import { createRoot } from "solid-js"
 import { isServer } from "solid-js/web"
 import { Persist, persisted } from "@/runtime/persistence/storage"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

 const initial = { list: [], hidden: {}, projects: {}, lastProject: {}, recentlyClosed: {} }

 function serverSchema(canonical?: () => string | undefined) {
-  return Codec.withInitial(serverState(canonical), initial)
+  return Persistence.withInitial(serverState(canonical), initial)
 }

 describe("server persistence schema", () => {
@@ -28,7 +29,7 @@ describe("server persistence schema", () => {
      ],
      projects: { local: [{ worktree: "/project", expanded: true }] },
    }
-    const state = Codec.decodeOrThrow(schema, input)
+    const state = Schema.decodeUnknownSync(schema)(input)
    expect(state).toEqual({
      list: [
        { type: "http", http: { url: "http://localhost:4096" } },
@@ -47,13 +48,13 @@ describe("server persistence schema", () => {
      recentlyClosed: {},
    })
    expect(input.list[1]).toHaveProperty("username", "legacy")
-    const encoded = schema.encode(state)
+    const encoded = Schema.encodeSync(schema)(state)
    expect(encoded).toEqual(state)
-    expect(Codec.decodeOrThrow(schema, encoded)).toEqual(state)
+    expect(Schema.decodeUnknownSync(schema)(encoded)).toEqual(state)
  })

  test("defaults missing or malformed fields and drops invalid entries independently", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(serverSchema(), input))
+    const decode = Schema.decodeUnknownSync(serverSchema())
    const empty = { list: [], hidden: {}, projects: {}, lastProject: {}, recentlyClosed: {} }
    expect(decode({})).toEqual(empty)
    expect(decode({ list: null, hidden: [], projects: false, lastProject: 1, recentlyClosed: "bad" })).toEqual(empty)
@@ -73,7 +74,7 @@ describe("server persistence schema", () => {

  test("moves canonical project buckets without changing server keys or unrelated scopes", () => {
    const schema = serverSchema(() => "https://opencode.example.com")
-    const state = Codec.decodeOrThrow(schema, {
+    const state = Schema.decodeUnknownSync(schema)({
      list: ["https://opencode.example.com"],
      hidden: { "https://opencode.example.com": true },
      projects: {
@@ -99,14 +100,14 @@ describe("server persistence schema", () => {
    expect(state.list[0]?.http.url).toBe("https://opencode.example.com")
    expect(state.hidden).toEqual({ "https://opencode.example.com": true })
    expect(state.recentlyClosed).toEqual({ local: ["/closed"], "https://opencode.example.com": ["/old-closed"] })
-    expect(schema.encode(state)).toEqual(state)
-    expect(Codec.decodeOrThrow(schema, state)).toEqual(state)
+    expect(Schema.encodeSync(schema)(state)).toEqual(state)
+    expect(Schema.decodeUnknownSync(schema)(state)).toEqual(state)
  })

  test("reads the latest canonical local prop on each decode", () => {
    const props: { canonicalLocalServer?: string } = {}
    const schema = serverSchema(() => props.canonicalLocalServer)
-    const decode = ((input: unknown) => Codec.decodeOrThrow(schema, input))
+    const decode = Schema.decodeUnknownSync(schema)
    const input = {
      projects: { remote: [{ worktree: "/project", expanded: true }] },
      lastProject: { remote: "/project" },
@@ -121,7 +122,7 @@ describe("server persistence schema", () => {
  })

  test("migrates a last project without a project list", () => {
-    expect(Codec.decodeOrThrow(serverSchema(() => "remote"), { lastProject: { remote: "/project" } })).toEqual({
+    expect(Schema.decodeUnknownSync(serverSchema(() => "remote"))({ lastProject: { remote: "/project" } })).toEqual({
      list: [],
      hidden: {},
      projects: {},
@@ -133,7 +134,7 @@ describe("server persistence schema", () => {

 describe("model persistence schema", () => {
  test("defaults missing state and keeps valid entries beside malformed entries", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(ModelState, { user: [], recent: [], variant: {} }), input))
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(ModelState, { user: [], recent: [], variant: {} }))
    expect(decode({})).toEqual({ user: [], recent: [], variant: {} })
    expect(decode({ user: null, recent: 1, variant: [] })).toEqual({ user: [], recent: [], variant: {} })
    const state = decode({
@@ -154,24 +155,24 @@ describe("model persistence schema", () => {
      recent: [{ providerID: "provider", modelID: "model" }],
      variant: { model: "high" },
    })
-    expect(ModelState.encode(state)).toEqual(state)
+    expect(Schema.encodeSync(ModelState)(state)).toEqual(state)
  })
 })

 describe("directory cache schemas", () => {
  test("defaults missing and malformed VCS caches but retains optional branch metadata", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(VcsState, { value: undefined }), input))
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(VcsState, { value: undefined }))
    expect(decode({})).toEqual({ value: undefined })
    expect(decode({ value: null })).toEqual({ value: undefined })
    expect(decode({ value: { branch: 1 } })).toEqual({ value: undefined })
    expect(decode({ value: { default_branch: "main" } })).toEqual({ value: { default_branch: "main" } })
    const state = decode({ value: { branch: "feature", default_branch: "main", obsolete: true } })
    expect(state).toEqual({ value: { branch: "feature", default_branch: "main" } })
-    expect(VcsState.encode(state)).toEqual(state)
+    expect(Schema.encodeSync(VcsState)(state)).toEqual(state)
  })

  test("validates project name, icon overrides and startup commands", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(ProjectState, { value: undefined }), input))
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(ProjectState, { value: undefined }))
    expect(decode({})).toEqual({ value: undefined })
    expect(decode({ value: [] })).toEqual({ value: undefined })
    expect(decode({ value: { icon: { override: 1 } } })).toEqual({ value: undefined })
@@ -184,7 +185,7 @@ describe("directory cache schemas", () => {
        commands: { start: "bun dev" },
      },
    })
-    expect(ProjectState.encode(state)).toEqual(state)
+    expect(Schema.encodeSync(ProjectState)(state)).toEqual(state)
    expect(state.value).toEqual({
      name: "Project",
      icon: { override: "data:image/png;base64,abc", color: "blue" },
@@ -193,12 +194,12 @@ describe("directory cache schemas", () => {
  })

  test("validates optional icon strings", () => {
-    const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(IconState, { value: undefined }), input))
+    const decode = Schema.decodeUnknownSync(Persistence.withInitial(IconState, { value: undefined }))
    expect(decode({})).toEqual({ value: undefined })
    expect(decode({ value: 42 })).toEqual({ value: undefined })
    expect(decode({ value: null })).toEqual({ value: undefined })
    expect(decode({ value: "" })).toEqual({ value: "" })
-    expect(IconState.encode(decode({ value: "data:image/png;base64,abc" }))).toEqual({
+    expect(Schema.encodeSync(IconState)(decode({ value: "data:image/png;base64,abc" }))).toEqual({
      value: "data:image/png;base64,abc",
    })
  })
@@ -254,7 +255,7 @@ test.skipIf(isServer)(
      const stored = values.get("opencode.global.dat:server")
      expect(stored).toBeDefined()
      if (!stored) throw new Error("server state was not written")
-      const decoded = Codec.decodeOrThrow(Codec.fromJsonString(serverSchema()), stored)
+      const decoded = Schema.decodeUnknownSync(Schema.fromJsonString(serverSchema()))(stored)
      expect(decoded.projects.local).toEqual([{ worktree: "/project", expanded: true }])
      expect(stored).not.toContain("username")
      expect(decoded.list).toEqual(root.state[0].list)
@@ -263,4 +264,3 @@ test.skipIf(isServer)(
    }
  },
 )
-
@@ -1,127 +1,136 @@
-import { Codec } from "@/runtime/persistence/codec"
-import { ServerKey } from "./key"
+import { Effect, Option, Schema, SchemaGetter } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"

-export { ServerKey }
+export const ServerKey = Schema.String.pipe(Schema.brand("ServerConnection.Key"))

-export const ServerHttpBase = Codec.struct({
-  url: Codec.string,
-  password: Codec.optional(Codec.string),
+export const ServerHttpBase = Persistence.struct({
+  url: Schema.String,
+  password: Schema.optional(Schema.String),
 })

-export const ServerHttp = Codec.struct({
-  type: Codec.literal("http"),
+export const ServerHttp = Persistence.struct({
+  type: Schema.Literal("http"),
  http: ServerHttpBase,
-  authToken: Codec.optional(Codec.boolean),
-  displayName: Codec.optional(Codec.string),
-  label: Codec.optional(Codec.string),
+  authToken: Schema.optional(Schema.Boolean),
+  displayName: Schema.optional(Schema.String),
+  label: Schema.optional(Schema.String),
 })

-// Servers were stored as a URL string, then as the HTTP block alone, before the current shape.
-const StoredServer = Codec.decodeTo(Codec.union([ServerHttp, ServerHttpBase, Codec.string]), ServerHttp, {
-  decode: (value) => {
-    if (typeof value === "string") return { type: "http" as const, http: { url: value } }
-    if ("http" in value) return value
-    return { type: "http" as const, http: value }
-  },
-  encode: (value) => value,
-})
-
-const ProjectList = Codec.lenientArray(
-  Codec.struct({
-    worktree: Codec.string,
-    expanded: Codec.fallback(Codec.boolean, () => true),
+const StoredServer = Schema.Union([ServerHttp, ServerHttpBase, Schema.String]).pipe(
+  Schema.decodeTo(ServerHttp, {
+    decode: SchemaGetter.transform((value) => {
+      if (typeof value === "string") return { type: "http", http: { url: value } }
+      if ("http" in value) return value
+      return { type: "http", http: value }
+    }),
+    encode: SchemaGetter.transform((value) => value),
  }),
 )
-const Projects = Codec.lenientRecord(ProjectList)
-const LastProject = Codec.fallback(Codec.sparseRecord(Codec.string), () => ({}))

-const State = Codec.struct({
-  list: Codec.lenientArray(StoredServer),
-  hidden: Codec.sparseRecord(Codec.boolean),
-  projects: Codec.record(ProjectList),
-  lastProject: Codec.sparseRecord(Codec.string),
-  recentlyClosed: Codec.record(Codec.lenientArray(Codec.string)),
+const ProjectList = Persistence.array(
+  Persistence.struct({
+    worktree: Schema.String,
+    expanded: Persistence.fallback(Schema.Boolean, () => true),
+  }),
+)
+const Projects = Persistence.record(ProjectList)
+const LastProject = Persistence.record(Schema.String.pipe(Schema.catchDecoding(() => Effect.succeed(Option.none()))))
+
+const State = Persistence.struct({
+  list: Persistence.array(StoredServer),
+  hidden: Schema.Record(
+    Schema.String,
+    Schema.mutableKey(Schema.Boolean.pipe(Schema.catchDecoding(() => Effect.succeed(Option.none())))),
+  ),
+  projects: Schema.Record(Schema.String, Schema.mutableKey(ProjectList)),
+  lastProject: Schema.Record(
+    Schema.String,
+    Schema.mutableKey(Schema.String.pipe(Schema.catchDecoding(() => Effect.succeed(Option.none())))),
+  ),
+  recentlyClosed: Schema.Record(Schema.String, Schema.mutableKey(Persistence.array(Schema.String))),
 })

-const StoredState = Codec.struct({ projects: Projects, lastProject: LastProject }, { preserve: true })
-
-// Projects and last-opened entries recorded under the canonical local server's URL move under
-// "local" when that URL is known, so they survive the server changing address.
 export function serverState(canonicalLocalServer: () => string | undefined = () => undefined) {
-  return Codec.migrate(
+  return Persistence.migrate(
    State,
-    Codec.transform(StoredState, {
-      decode: (value) => {
-        const canonical = canonicalLocalServer()
-        if (!canonical || canonical === "local") return value
-        const previous = value.projects[canonical]
-        const last = value.lastProject[canonical]
-        if (!previous && last === undefined) return value
+    Schema.Struct({ projects: Projects, lastProject: LastProject }).pipe(
+      Schema.decode({
+        decode: SchemaGetter.transform((value) => {
+          const canonical = canonicalLocalServer()
+          if (!canonical || canonical === "local") return value
+          const previous = value.projects[canonical]
+          const last = value.lastProject[canonical]
+          if (!previous && last === undefined) return value

-        const projects = { ...value.projects }
-        if (previous) {
-          const local = projects.local ?? []
-          const worktrees = new Set(local.map((project) => project.worktree))
-          projects.local = [
-            ...local,
-            ...previous.filter((project) => {
-              if (worktrees.has(project.worktree)) return false
-              worktrees.add(project.worktree)
-              return true
-            }),
-          ]
-          delete projects[canonical]
-        }
-        const lastProject = { ...value.lastProject }
-        if (last !== undefined) {
-          lastProject.local ??= last
-          delete lastProject[canonical]
-        }
-        return { ...value, projects, lastProject }
-      },
-      encode: (value) => value,
-    }),
+          const projects = { ...value.projects }
+          if (previous) {
+            const local = projects.local ?? []
+            const worktrees = new Set(local.map((project) => project.worktree))
+            projects.local = [
+              ...local,
+              ...previous.filter((project) => {
+                if (worktrees.has(project.worktree)) return false
+                worktrees.add(project.worktree)
+                return true
+              }),
+            ]
+            delete projects[canonical]
+          }
+          const lastProject = { ...value.lastProject }
+          if (last !== undefined) {
+            lastProject.local ??= last
+            delete lastProject[canonical]
+          }
+          return { ...value, projects, lastProject }
+        }),
+        encode: SchemaGetter.transform((value) => value),
+      }),
+    ),
  )
 }

-export const ModelState = Codec.struct({
-  user: Codec.lenientArray(
-    Codec.struct({
-      providerID: Codec.string,
-      modelID: Codec.string,
-      visibility: Codec.literals(["show", "hide"]),
-      favorite: Codec.optional(Codec.boolean),
+export const ModelState = Persistence.struct({
+  user: Persistence.array(
+    Persistence.struct({
+      providerID: Schema.String,
+      modelID: Schema.String,
+      visibility: Schema.Literals(["show", "hide"]),
+      favorite: Schema.optional(Schema.Boolean),
    }),
  ),
-  recent: Codec.lenientArray(Codec.struct({ providerID: Codec.string, modelID: Codec.string })),
-  variant: Codec.sparseRecord(Codec.undefinedOr(Codec.string)),
+  recent: Persistence.array(Persistence.struct({ providerID: Schema.String, modelID: Schema.String })),
+  variant: Schema.Record(
+    Schema.String,
+    Schema.mutableKey(
+      Schema.UndefinedOr(Schema.String).pipe(Schema.catchDecoding(() => Effect.succeed(Option.none()))),
+    ),
+  ),
 })

-export const VcsState = Codec.struct({
-  value: Codec.optional(
-    Codec.struct({
-      branch: Codec.optional(Codec.string),
-      default_branch: Codec.optional(Codec.string),
+export const VcsState = Persistence.struct({
+  value: Schema.optional(
+    Persistence.struct({
+      branch: Schema.optional(Schema.String),
+      default_branch: Schema.optional(Schema.String),
    }),
  ),
 })

-const ProjectMeta = Codec.struct({
-  name: Codec.optional(Codec.string),
-  icon: Codec.optional(
-    Codec.struct({
-      override: Codec.optional(Codec.string),
-      color: Codec.optional(Codec.string),
+const ProjectMeta = Persistence.struct({
+  name: Schema.optional(Schema.String),
+  icon: Schema.optional(
+    Persistence.struct({
+      override: Schema.optional(Schema.String),
+      color: Schema.optional(Schema.String),
    }),
  ),
-  commands: Codec.optional(Codec.struct({ start: Codec.optional(Codec.string) })),
+  commands: Schema.optional(Persistence.struct({ start: Schema.optional(Schema.String) })),
 })

-export const ProjectState = Codec.struct({
-  value: Codec.optional(ProjectMeta),
+export const ProjectState = Persistence.struct({
+  value: Schema.optional(ProjectMeta),
 })

-export const IconState = Codec.struct({
-  value: Codec.optional(Codec.string),
+export const IconState = Persistence.struct({
+  value: Schema.optional(Schema.String),
 })
-
@@ -1,12 +1,13 @@
 import { describe, expect, test } from "bun:test"
 import { canRemoveServer, createServerProjects, resolveServerList, ServerConnection } from "./registry"
+import { Schema } from "effect"
 import { serverState } from "./persistence"
 import { createStore } from "solid-js/store"
 import { ServerScope } from "./scope"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

 function serverSchema() {
-  return Codec.withInitial(serverState(), {
+  return Persistence.withInitial(serverState(), {
    list: [],
    hidden: {},
    projects: {},
@@ -18,7 +19,7 @@ function serverSchema() {
 describe("resolveServerList", () => {
  test("lets startup auth_token credentials override a persisted same-url server", () => {
    const list = resolveServerList({
-      stored: Codec.decodeOrThrow(serverSchema(), { list: [{ url: "https://server.example.test" }] }).list,
+      stored: Schema.decodeUnknownSync(serverSchema())({ list: [{ url: "https://server.example.test" }] }).list,
      props: [
        {
          type: "http",
@@ -43,7 +44,7 @@ describe("resolveServerList", () => {

  test("keeps persisted credentials when startup has no auth_token", () => {
    const list = resolveServerList({
-      stored: Codec.decodeOrThrow(serverSchema(), {
+      stored: Schema.decodeUnknownSync(serverSchema())({
        list: [{ url: "https://server.example.test", password: "saved" }],
      }).list,
      props: [{ type: "http", http: { url: "https://server.example.test" } }],
@@ -76,7 +77,7 @@ test("treats WSL sidecars as remote server connections", () => {
 })

 test("keeps exact persisted server identities and prevents removing provided servers", () => {
-  const stored = Codec.decodeOrThrow(serverSchema(), {
+  const stored = Schema.decodeUnknownSync(serverSchema())({
    list: ["http://localhost:4096", "http://localhost:4096/", "http://127.0.0.1:4096"],
  }).list
  expect(resolveServerList({ stored }).map((server) => String(ServerConnection.key(server)))).toEqual([
@@ -90,7 +91,7 @@ test("keeps exact persisted server identities and prevents removing provided ser
 })

 test("project actions update schema-derived state and follow dynamic server scopes", () => {
-  const [store, setStore] = createStore(Codec.decodeOrThrow(serverSchema(), {}))
+  const [store, setStore] = createStore(Schema.decodeUnknownSync(serverSchema())({}))
  const props: { server: ServerConnection.Key; canonicalLocalServer?: ServerConnection.Key } = {
    server: ServerConnection.Key.make("https://remote.example"),
  }
@@ -114,4 +115,3 @@ test("project actions update schema-derived state and follow dynamic server scop
  expect(store.projects.local).toEqual([{ worktree: "/local", expanded: true }])
  expect(store.projects[props.server]).toEqual([{ worktree: "/remote", expanded: false }])
 })
-
@@ -1,12 +1,12 @@
-import { Codec } from "@/runtime/persistence/codec"
+import { Option, Schema } from "effect"
 import { normalizeServerUrl } from "@/runtime/server/registry"

-const pairing = Codec.fromJsonString(
-  Codec.struct({
-    urls: Codec.array(Codec.string),
-    username: Codec.literal("opencode"),
-    password: Codec.string,
-  }),
+const pairing = Schema.fromJsonString(
+  Schema.Struct({
+    urls: Schema.Array(Schema.String),
+    username: Schema.Literal("opencode"),
+    password: Schema.String,
+  }),
 )

 export function serverAddress(value: string) {
@@ -20,10 +20,9 @@ export function serverAddress(value: string) {
 }

 export function decodePairingCode(value: string) {
-  const result = Codec.decodeOption(pairing, value)
-  if (!result) return
-  const urls = [...new Set(result.urls.map(serverAddress).filter((url) => url !== undefined))]
-  if (!urls.length) return
-  return { urls, password: result.password }
+  const result = Schema.decodeUnknownOption(pairing)(value)
+  if (Option.isNone(result)) return
+  const urls = [...new Set(result.value.urls.map(serverAddress).filter((url) => url !== undefined))]
+  if (!urls.length) return
+  return { urls, password: result.value.password }
 }
-
@@ -1,3 +1,4 @@
+import { Effect, Fiber } from "effect"
 import { createEffect, onCleanup } from "solid-js"
 import { createStore } from "solid-js/store"
 import type { SshConfig, SshItem, SshPlatform } from "./types"
@@ -23,8 +24,7 @@ export function createSshController(input: {
      | undefined
    >
  >({})
-  // One in-flight request per server; cancelling settles it immediately and ignores its outcome.
-  const tasks = new Map<string, { cancelled: boolean }>()
+  const tasks = new Map<string, Fiber.Fiber<void>>()
  const item = (id: string) => input.items().find((item) => item.config.id === id)
  const settle = (id: string) => {
    const attempt = attempts[id]
@@ -33,32 +33,31 @@ export function createSshController(input: {
    setAttempts(id, { active: false, onConnected: undefined })
    if (item(id)?.stage === "ready" && onConnected) queueMicrotask(onConnected)
  }
-  const finish = (id: string, task: { cancelled: boolean }) => {
-    if (task.cancelled) return
-    task.cancelled = true
-    if (tasks.get(id) === task) tasks.delete(id)
-    setAttempts(id, "submitting", false)
-  }
-  const interrupt = (id: string) => {
-    const task = tasks.get(id)
-    if (task) finish(id, task)
-  }
-  const run = (id: string, work: () => Promise<unknown>) => {
-    setAttempts(id, { submitting: true, error: false })
-    const task = { cancelled: false }
-    tasks.set(id, task)
-    work().then(
-      () => finish(id, task),
-      () => {
-        if (task.cancelled) return
-        setAttempts(id, "error", true)
-        if (!attempts[id]?.prompted) input.error()
-        finish(id, task)
-      },
-    )
-  }
-  onCleanup(() => {
-    for (const id of [...tasks.keys()]) interrupt(id)
+  const run = (id: string, effect: Effect.Effect<unknown, unknown>) => {
+    setAttempts(id, { submitting: true, error: false })
+    tasks.set(
+      id,
+      Effect.runFork(
+        effect.pipe(
+          Effect.asVoid,
+          Effect.catch(() =>
+            Effect.sync(() => {
+              setAttempts(id, "error", true)
+              if (!attempts[id]?.prompted) input.error()
+            }),
+          ),
+          Effect.ensuring(
+            Effect.sync(() => {
+              tasks.delete(id)
+              setAttempts(id, "submitting", false)
+            }),
+          ),
+        ),
+      ),
+    )
+  }
+  onCleanup(() => {
+    Effect.runFork(Effect.forEach([...tasks.values()], Fiber.interrupt, { discard: true }))
  })
  createEffect(() => {
    for (const item of input.items()) {
@@ -115,32 +114,40 @@ export function createSshController(input: {
        error: false,
        onConnected: options?.onConnected ?? (options?.replace ? attempts[config.id]?.onConnected : undefined),
      })
-      run(config.id, async () => {
-        await api.start({ ...config, replace: options?.replace })
-        // Observe admission before treating an older disconnected snapshot as cancellation.
-        await input.refresh()
-      })
+      run(
+        config.id,
+        Effect.gen(function* () {
+          yield* Effect.tryPromise(() => api.start({ ...config, replace: options?.replace }))
+          // Observe admission before treating an older disconnected snapshot as cancellation.
+          yield* Effect.tryPromise(input.refresh)
+        }),
+      )
    },
    respond: (id: string, prompt: string, value: string) => {
      const api = input.api
      if (!api || item(id)?.prompt?.id !== prompt || attempts[id]?.submitting) return
      if (attempts[id]?.answered === prompt && !attempts[id]?.error) return
      setAttempts(id, "answered", prompt)
-      run(id, () => api.respond(id, prompt, value))
+      run(
+        id,
+        Effect.tryPromise(() => api.respond(id, prompt, value)),
+      )
    },
-    cancel: (id: string) => {
-      const api = input.api
-      interrupt(id)
-      setAttempts(id, undefined)
-      if (!api) return
-      void api
-        .cancel(id)
-        .then(() => (item(id)?.saved ? undefined : api.forget(id)))
-        .catch(() => undefined)
+    cancel: (id: string) => {
+      const task = tasks.get(id)
+      const api = input.api
+      Effect.runFork(
+        Effect.gen(function* () {
+          if (task) yield* Fiber.interrupt(task)
+          setAttempts(id, undefined)
+          if (!api) return
+          yield* Effect.tryPromise(() => api.cancel(id))
+          if (!item(id)?.saved) yield* Effect.tryPromise(() => api.forget(id))
+        }).pipe(Effect.ignore),
+      )
    },
    restore: (config: SshConfig) => input.api?.start({ ...config, background: true }),
    disconnect: (id: string) => input.api?.disconnect(id),
    forget: (id: string) => input.api?.forget(id),
  }
 }
-
@@ -1,61 +0,0 @@
-import { Schema } from "effect"
-
-// The SSH state contract between the desktop main process and its renderer. Only the main process
-// needs the schemas (its RPC server validates with them); the renderer imports the types from ./types.
-
-export const SshConfig = Schema.Struct({ id: Schema.String, target: Schema.String, name: Schema.String })
-export type SshConfig = typeof SshConfig.Type
-export const SshHttp = Schema.Struct({ url: Schema.String, password: Schema.String })
-export type SshHttp = typeof SshHttp.Type
-export const SshStage = Schema.Literals([
-  "disconnected",
-  "connecting",
-  "checking",
-  "downloading",
-  "uploading",
-  "starting",
-  "ready",
-  "authentication",
-  "incompatible",
-  "failed",
-])
-export const SshPrompt = Schema.Struct({
-  id: Schema.String,
-  text: Schema.String,
-  confirm: Schema.Boolean,
-})
-export const SshItem = Schema.Struct({
-  config: SshConfig,
-  saved: Schema.Boolean,
-  destination: Schema.optional(Schema.String),
-  stage: SshStage,
-  http: Schema.optional(SshHttp),
-  prompt: Schema.optional(SshPrompt),
-  authenticatingElsewhere: Schema.optional(Schema.Boolean),
-  detail: Schema.String,
-  error: Schema.optional(
-    Schema.Literals([
-      "connection",
-      "input",
-      "platform",
-      "version",
-      "install",
-      "service",
-      "host-key",
-      "ssh-missing",
-      "unpublished",
-    ]),
-  ),
-})
-export type SshItem = typeof SshItem.Type
-export const SshState = Schema.Struct({ servers: Schema.Array(SshItem) })
-export type SshState = typeof SshState.Type
-export const SshStart = Schema.Struct({
-  id: Schema.String,
-  target: Schema.String,
-  name: Schema.String,
-  replace: Schema.optional(Schema.Boolean),
-  background: Schema.optional(Schema.Boolean),
-})
-export type SshStart = typeof SshStart.Type
-
@@ -1,9 +1,63 @@
-export { sshHostname, sshName } from "./name"
-export { isSshConnecting } from "./status"
-import type { SshConfig, SshHttp, SshItem, SshStart, SshState } from "./schema"
-
-export type { SshConfig, SshHttp, SshItem, SshStart, SshState }
-
+import { Schema } from "effect"
+export { sshHostname, sshName } from "./name"
+export { isSshConnecting } from "./status"
+
+export const SshConfig = Schema.Struct({ id: Schema.String, target: Schema.String, name: Schema.String })
+export type SshConfig = typeof SshConfig.Type
+export const SshHttp = Schema.Struct({ url: Schema.String, password: Schema.String })
+export type SshHttp = typeof SshHttp.Type
+export const SshStage = Schema.Literals([
+  "disconnected",
+  "connecting",
+  "checking",
+  "downloading",
+  "uploading",
+  "starting",
+  "ready",
+  "authentication",
+  "incompatible",
+  "failed",
+])
+export const SshPrompt = Schema.Struct({
+  id: Schema.String,
+  text: Schema.String,
+  confirm: Schema.Boolean,
+})
+export const SshItem = Schema.Struct({
+  config: SshConfig,
+  saved: Schema.Boolean,
+  destination: Schema.optional(Schema.String),
+  stage: SshStage,
+  http: Schema.optional(SshHttp),
+  prompt: Schema.optional(SshPrompt),
+  authenticatingElsewhere: Schema.optional(Schema.Boolean),
+  detail: Schema.String,
+  error: Schema.optional(
+    Schema.Literals([
+      "connection",
+      "input",
+      "platform",
+      "version",
+      "install",
+      "service",
+      "host-key",
+      "ssh-missing",
+      "unpublished",
+    ]),
+  ),
+})
+export type SshItem = typeof SshItem.Type
+export const SshState = Schema.Struct({ servers: Schema.Array(SshItem) })
+export type SshState = typeof SshState.Type
+export const SshStart = Schema.Struct({
+  id: Schema.String,
+  target: Schema.String,
+  name: Schema.String,
+  replace: Schema.optional(Schema.Boolean),
+  background: Schema.optional(Schema.Boolean),
+})
+export type SshStart = typeof SshStart.Type
+
 export type SshPlatform = {
  getState(): Promise<SshState>
  subscribe(callback: (state: SshState) => void): () => void
@@ -16,5 +70,3 @@ export type SshPlatform = {
  forget(id: string): Promise<void>
  openConfig(): Promise<void>
 }
-
-
@@ -20,13 +20,18 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
  const command = useCommand()
  const state = props.browser.active
  const address = () => (state()?.url === "about:blank" ? "" : (state()?.url ?? ""))
+  const failed = () => !!state()?.loadError
  const registration = props.browser.registration
  const button = { variant: "ghost", size: "large" } as const
  const [store, setStore] = createStore({
    address: "",
    editing: false,
+    submitted: false,
+    // A submitted navigation the browser has not reported yet; keeps the empty state hidden meanwhile.
+    navigating: false,
    visible: typeof document === "undefined" || document.visibilityState === "visible",
  })
+  const empty = () => !address() && !state()?.loading && !store.navigating
  let surface: HTMLDivElement | undefined
  let addressDisplay: HTMLDivElement | undefined
  let frame: number | undefined
@@ -43,7 +48,7 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
      title: language.t("command.browser.reload"),
      category: language.t("command.category.view"),
      keybind: "f5",
-      disabled: !props.visible || !state(),
+      disabled: !props.visible || !address(),
      onSelect: () => {
        const tab = state()
        if (tab) props.browser.command({ type: "reload", tabID: tab.id })
@@ -71,7 +76,9 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
    const top = Math.round(rect.top * zoom)
    const right = Math.round(rect.right * zoom)
    const bottom = Math.round(rect.bottom * zoom)
-    const visible = props.visible && store.visible && !dialog.active && !covered(rect)
+    // The desktop page hides blank and loading documents itself; only hide here
+    // while the pane shows its own empty or failed state over the surface.
+    const visible = props.visible && store.visible && !empty() && !failed() && !dialog.active && !covered(rect)
    // The cutout exposes the app backdrop outside the rounded Review card,
    // not the browser surface inside it.
    const color = getComputedStyle(
@@ -107,7 +114,25 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
    if (frame === undefined) frame = requestAnimationFrame(tick)
  }

-  createEffect(() => !store.editing && setStore("address", address()))
+  createEffect(on([() => state()?.id, address], () => !store.editing && setStore("address", address())))
+  // Any reported movement, including a rejected or blocked request, ends the submitted navigation.
+  createEffect(
+    on(
+      [() => state()?.id, () => state()?.generation, () => state()?.loading, () => props.browser.error()],
+      () => setStore("navigating", false),
+      { defer: true },
+    ),
+  )
+  // A blocked or rejected submission leaves the page where it was; show that page's URL again.
+  createEffect(
+    on(
+      () => props.browser.error(),
+      (error) => {
+        if (error && !store.editing) setStore("address", address())
+      },
+      { defer: true },
+    ),
+  )
  createEffect(
    on(registration, (current) => {
      // Session routes can change before this pane unmounts. Hide the registration
@@ -123,6 +148,8 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
        () => store.visible,
        () => props.visible,
        () => state()?.id,
+        empty,
+        failed,
        registration,
      ],
      () => {
@@ -157,7 +184,7 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes

  return (
    <aside id="browser-panel" class="relative size-full min-w-0 overflow-hidden bg-v2-background-bg-base flex flex-col">
-      <div class="h-10 shrink-0 flex items-center gap-1 px-2 border-b border-v2-border-border-muted">
+      <div class="h-10 shrink-0 flex items-center gap-1 px-3 border-b border-v2-border-border-muted">
        <For each={["back", "forward"] as const}>
          {(direction) => (
            <Tooltip placement="top" value={language.t(direction === "back" ? "common.goBack" : "common.goForward")}>
@@ -193,7 +220,7 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
        >
          <IconButton
            {...button}
-            disabled={!state()}
+            disabled={!state()?.loading && !address()}
            aria-label={language.t(state()?.loading ? "prompt.action.stop" : "error.page.action.reload")}
            onClick={() => {
              const tab = state()
@@ -212,8 +239,13 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
          onSubmit={(event) => {
            event.preventDefault()
            const tab = state()
-            if (tab && store.address.trim())
-              props.browser.command({ type: "navigate", tabID: tab.id, url: store.address })
+            const url = store.address.trim()
+            if (!tab) return
+            if (url || failed()) {
+              setStore({ submitted: true, address: url, navigating: true })
+              props.browser.command({ type: "navigate", tabID: tab.id, url: url || "about:blank" })
+            }
+            event.currentTarget.querySelector("input")?.blur()
          }}
        >
          <input
@@ -224,8 +256,14 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
            disabled={!state()}
            placeholder={language.t("session.browser.address.placeholder")}
            aria-label={language.t("session.browser.address")}
-            onFocus={() => setStore("editing", true)}
-            onBlur={() => setStore({ editing: false, address: address() })}
+            onFocus={(event) => {
+              setStore("editing", true)
+              event.currentTarget.select()
+            }}
+            onClick={(event) => event.currentTarget.select()}
+            onBlur={() =>
+              setStore({ editing: false, address: store.submitted ? store.address : address(), submitted: false })
+            }
            onInput={(event) => setStore("address", event.currentTarget.value)}
            onScroll={(event) => {
              if (addressDisplay) addressDisplay.scrollLeft = event.currentTarget.scrollLeft
@@ -243,12 +281,27 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
          </div>
        </form>
      </div>
-      <Show when={props.browser.error()}>
+      <Show when={props.browser.error() && !failed()}>
        <div class="shrink-0 px-3 py-1.5 text-12-regular text-text-danger-base border-b border-v2-border-border-muted">
          {props.browser.error()}
        </div>
      </Show>
      <div ref={surface} class="min-h-0 flex-1 bg-v2-background-bg-base flex items-center justify-center">
+        <Show when={(empty() || failed()) && !props.browser.suspended()}>
+          {/* Add the 40px toolbar to the file empty state's 160px bottom padding to align their centers. */}
+          <div
+            dir="auto"
+            class="flex size-full flex-col items-center justify-center gap-2 p-6 pb-[200px] text-center text-text-weak"
+          >
+            <Icon name="globe" size="large" class="mb-2 shrink-0" />
+            <div class="text-[13px] font-medium leading-[var(--line-height-compact)] text-text-strong">
+              {language.t(failed() ? "session.browser.failed.title" : "session.browser.empty.title")}
+            </div>
+            <div class="text-13-regular leading-[var(--line-height-base)]">
+              {language.t(failed() ? "session.browser.failed.description" : "session.browser.empty.description")}
+            </div>
+          </div>
+        </Show>
        <Show when={props.browser.suspended()}>
          <p class="px-6 text-center text-13-regular text-v2-text-text-subtle" role="status">
            {language.t("session.browser.suspended")}
@@ -1,8 +1,9 @@
 import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
 import { OPEN_APPS, OpenAppPreferences } from "./open-in-app"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

-const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(OpenAppPreferences, { app: "finder" }), input))
+const decode = Schema.decodeUnknownSync(Persistence.withInitial(OpenAppPreferences, { app: "finder" }))

 describe("open app preferences", () => {
  test.each([...OPEN_APPS])("preserves the %s preference", (app) => {
@@ -17,4 +18,3 @@ describe("open app preferences", () => {
    expect(decode({})).toEqual({ app: "finder" })
  })
 })
-
@@ -5,7 +5,8 @@ import { usePlatform } from "@/runtime/platform/platform"
 import { Persist, persisted } from "@/runtime/persistence/storage"
 import { showToast } from "@/shell/notifications/toast"
 import { useServer } from "@/runtime/server/current"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"
 import { fileManagerApp } from "@/home/projects/file-manager"
 import { openInAppParentPath } from "@/session/files/open-in-app-path"

@@ -29,8 +30,8 @@ export const OPEN_APPS = [
 export type OpenApp = (typeof OPEN_APPS)[number]
 export type OpenAppOS = "macos" | "windows" | "linux" | "unknown"

-export const OpenAppPreferences = Codec.struct({
-  app: Codec.literals(OPEN_APPS),
+export const OpenAppPreferences = Persistence.struct({
+  app: Schema.Literals(OPEN_APPS),
 })

 const appExistence = new Map<string, Promise<boolean>>()
@@ -241,4 +242,3 @@ function checkAppExists(platform: ReturnType<typeof usePlatform>, app: string) {
  appExistence.set(app, request)
  return request
 }
-
@@ -1,6 +1,8 @@
 import { children, createMemo, Show } from "solid-js"
 import type { JSX } from "solid-js"
 import { useSortable } from "@dnd-kit/solid/sortable"
+import { Icon } from "@opencode/ui/icon"
+import { IconButton } from "@opencode/ui/icon-button"
 import { Keybind } from "@opencode/ui/keybind"
 import { Tooltip } from "@opencode/ui/tooltip"
 import { Tabs } from "@opencode/ui/tabs"
@@ -69,9 +71,19 @@ export function SortableTab(props: {
              placement="bottom"
              gutter={10}
            >
-              <Tabs.CloseButton
-                class="h-5 w-5"
-                onClick={() => props.onTabClose(props.tab)}
+              <IconButton
+                size="small"
+                variant="ghost-muted"
+                onPointerDown={(event) => {
+                  event.preventDefault()
+                  event.stopPropagation()
+                }}
+                onClick={(event) => {
+                  event.preventDefault()
+                  event.stopPropagation()
+                  props.onTabClose(props.tab)
+                }}
+                icon={<Icon name="xmark-small" />}
                aria-label={language.t("common.closeTab")}
              />
            </Tooltip>
@@ -5,20 +5,17 @@ import {
  type SessionReviewExpandMode,
 } from "@opencode/session-ui/v2/session-review-v2"
 import { createSignal } from "solid-js"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
 import type { Platform } from "@/runtime/platform/platform"
 import { Persist, persisted } from "@/runtime/persistence/storage"
+import { Persistence } from "@/runtime/persistence/schema"

-const ReviewPanel = Codec.struct({
-  sidebarOpened: Codec.boolean,
-  sidebarWidth: Codec.make<number, number>(
-    (v) =>
-      typeof v === "number" && v >= SESSION_REVIEW_V2_SIDEBAR_WIDTH_MIN && v <= SESSION_REVIEW_V2_SIDEBAR_WIDTH_MAX
-        ? v
-        : Codec.INVALID,
-    (v) => v,
-  ),
-  expandMode: Codec.literals(["expand", "collapse"]),
+const ReviewPanel = Persistence.struct({
+  sidebarOpened: Schema.Boolean,
+  sidebarWidth: Schema.Finite.check(
+    Schema.isBetween({ minimum: SESSION_REVIEW_V2_SIDEBAR_WIDTH_MIN, maximum: SESSION_REVIEW_V2_SIDEBAR_WIDTH_MAX }),
+  ),
+  expandMode: Schema.Literals(["expand", "collapse"]),
 })

 export function createReviewPanelState(platform?: Platform) {
@@ -50,4 +47,3 @@ export function createReviewPanelState(platform?: Platform) {
 }

 export type ReviewPanelState = ReturnType<typeof createReviewPanelState>
-
@@ -2,8 +2,9 @@ import { beforeAll, describe, expect, mock, test } from "bun:test"
 import { ServerScope } from "@/runtime/server/scope"
 import { base64Encode } from "@opencode/util/encode"
 import { Persist } from "@/runtime/persistence/storage"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"
 import type { Platform } from "@/runtime/platform/platform"
+import { Schema } from "effect"

 let getWorkspaceTerminalCacheKey: typeof import("./context").getWorkspaceTerminalCacheKey
 let clearWorkspaceTerminals: typeof import("./context").clearWorkspaceTerminals
@@ -20,10 +21,10 @@ beforeAll(async () => {
  const mod = await import("./context")
  getWorkspaceTerminalCacheKey = mod.getWorkspaceTerminalCacheKey
  clearWorkspaceTerminals = mod.clearWorkspaceTerminals
-  const schema = Codec.withInitial(mod.TerminalState, { all: [] })
-  decodeTerminalState = ((input: unknown) => Codec.decodeOrThrow(schema, input))
+  const schema = Persistence.withInitial(mod.TerminalState, { all: [] })
+  decodeTerminalState = Schema.decodeUnknownSync(schema)
  roundTripTerminalState = (value) =>
-    Codec.decodeOrThrow(schema, schema.encode(Codec.decodeOrThrow(schema, value)))
+    Schema.decodeUnknownSync(schema)(Schema.encodeSync(schema)(Schema.decodeUnknownSync(schema)(value)))
 })

 describe("getWorkspaceTerminalCacheKey", () => {
@@ -140,4 +141,3 @@ describe("TerminalState", () => {
    expect(roundTripTerminalState(value)).toEqual(value)
  })
 })
-
@@ -8,20 +8,18 @@ import { base64Encode } from "@opencode/util/encode"
 import { defaultTitle, titleNumber } from "./title"
 import { Persist, persisted, removePersisted } from "@/runtime/persistence/storage"
 import { ScopedKey, ServerScope } from "@/runtime/server/scope"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"
+import { Schema, SchemaGetter } from "effect"

-const PTY = Codec.struct({
-  id: Codec.make<string, string>(
-    (v) => (typeof v === "string" && v.length > 0 ? v : Codec.INVALID),
-    (v) => v,
-  ),
-  title: Codec.fallback(Codec.string, () => ""),
-  titleNumber: Codec.fallback(Codec.number, () => 0),
-  rows: Codec.lenientOptional(Codec.number),
-  cols: Codec.lenientOptional(Codec.number),
-  buffer: Codec.lenientOptional(Codec.string),
-  scrollY: Codec.lenientOptional(Codec.number),
-  cursor: Codec.lenientOptional(Codec.number),
+const PTY = Persistence.struct({
+  id: Schema.NonEmptyString,
+  title: Persistence.fallback(Schema.String, () => ""),
+  titleNumber: Persistence.fallback(Schema.Finite, () => 0),
+  rows: Persistence.optional(Schema.Finite),
+  cols: Persistence.optional(Schema.Finite),
+  buffer: Persistence.optional(Schema.String),
+  scrollY: Persistence.optional(Schema.Finite),
+  cursor: Persistence.optional(Schema.Finite),
 })

 export type LocalPTY = typeof PTY.Type
@@ -33,26 +31,28 @@ function numberFromTitle(title: string) {
  return titleNumber(title, MAX_TERMINAL_SESSIONS)
 }

-const State = Codec.struct({
-  active: Codec.lenientOptional(Codec.string),
-  all: Codec.lenientArray(PTY),
+const State = Persistence.struct({
+  active: Persistence.optional(Schema.String),
+  all: Persistence.array(PTY),
 })

-export const TerminalState = Codec.transform(State, {
-  decode: (value): typeof State.Type => {
-    const seen = new Set<string>()
-    const all = value.all.flatMap((pty) => {
-      if (seen.has(pty.id)) return []
-      seen.add(pty.id)
-      return [{ ...pty, titleNumber: pty.titleNumber > 0 ? pty.titleNumber : (numberFromTitle(pty.title) ?? 0) }]
-    })
-    return {
-      active: value.active && seen.has(value.active) ? value.active : all[0]?.id,
-      all,
-    }
-  },
-  encode: (value) => value,
-})
+export const TerminalState = State.pipe(
+  Schema.decodeTo(Schema.toType(State), {
+    decode: SchemaGetter.transform((value) => {
+      const seen = new Set<string>()
+      const all = value.all.flatMap((pty) => {
+        if (seen.has(pty.id)) return []
+        seen.add(pty.id)
+        return [{ ...pty, titleNumber: pty.titleNumber > 0 ? pty.titleNumber : (numberFromTitle(pty.title) ?? 0) }]
+      })
+      return {
+        active: value.active && seen.has(value.active) ? value.active : all[0]?.id,
+        all,
+      }
+    }),
+    encode: SchemaGetter.transform((value) => value),
+  }),
+)

 export function getWorkspaceTerminalCacheKey(dir: string, scope: ServerScope = ServerScope.local) {
  return ScopedKey.from(scope, dir, WORKSPACE_KEY)
@@ -458,5 +458,3 @@ export const { use: useTerminal, provider: TerminalProvider } = createSimpleCont
    }
  },
 })
-
-
@@ -1,40 +1,40 @@
-import { describe, expect, test } from "bun:test"
-import { GoUpsellState } from "./usage-exceeded-dialogs"
-import { Codec } from "@/runtime/persistence/codec"
-
-const schema = Codec.withInitial(GoUpsellState, {
-  go_upsell_last_seen_at: null,
-  go_upsell_dont_show: null,
-  go_upsell_account_rate_limit_last_seen_at: null,
-  go_upsell_account_rate_limit_dont_show: null,
-})
-const decode = (input: unknown) => Codec.decodeOrThrow(schema, input)
-
-describe("usage exceeded preferences", () => {
-  test("defaults unseen prompts", () => {
-    expect(decode({})).toEqual({
-      go_upsell_last_seen_at: null,
-      go_upsell_dont_show: null,
-      go_upsell_account_rate_limit_last_seen_at: null,
-      go_upsell_account_rate_limit_dont_show: null,
-    })
-  })
-
-  test("preserves timestamps while recovering malformed siblings", () => {
-    expect(
-      decode({
-        go_upsell_last_seen_at: 123,
-        go_upsell_dont_show: "true",
-        go_upsell_account_rate_limit_last_seen_at: Infinity,
-        go_upsell_account_rate_limit_dont_show: 456,
-      }),
-    ).toEqual({
-      go_upsell_last_seen_at: 123,
-      go_upsell_dont_show: null,
-      go_upsell_account_rate_limit_last_seen_at: null,
-      go_upsell_account_rate_limit_dont_show: 456,
-    })
-  })
-})
-
-
+import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
+import { GoUpsellState } from "./usage-exceeded-dialogs"
+import { Persistence } from "@/runtime/persistence/schema"
+
+const decode = Schema.decodeUnknownSync(
+  Persistence.withInitial(GoUpsellState, {
+    go_upsell_last_seen_at: null,
+    go_upsell_dont_show: null,
+    go_upsell_account_rate_limit_last_seen_at: null,
+    go_upsell_account_rate_limit_dont_show: null,
+  }),
+)
+
+describe("usage exceeded preferences", () => {
+  test("defaults unseen prompts", () => {
+    expect(decode({})).toEqual({
+      go_upsell_last_seen_at: null,
+      go_upsell_dont_show: null,
+      go_upsell_account_rate_limit_last_seen_at: null,
+      go_upsell_account_rate_limit_dont_show: null,
+    })
+  })
+
+  test("preserves timestamps while recovering malformed siblings", () => {
+    expect(
+      decode({
+        go_upsell_last_seen_at: 123,
+        go_upsell_dont_show: "true",
+        go_upsell_account_rate_limit_last_seen_at: Infinity,
+        go_upsell_account_rate_limit_dont_show: 456,
+      }),
+    ).toEqual({
+      go_upsell_last_seen_at: 123,
+      go_upsell_dont_show: null,
+      go_upsell_account_rate_limit_last_seen_at: null,
+      go_upsell_account_rate_limit_dont_show: 456,
+    })
+  })
+})
@@ -2,7 +2,8 @@ import { useWorkspaceLocation } from "@/workspaces/location"
 import { Persist, persisted } from "@/runtime/persistence/storage"
 import type { SessionStatus } from "@opencode/client/promise"
 import { onCleanup } from "solid-js"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"
 import { useSessionLayout } from "./session-layout"
 import { useDialog, useI18n } from "@opencode/ui/context"
 import { DialogUsageExceeded } from "@/providers/connect/usage-exceeded"
@@ -14,11 +15,11 @@ const GO_UPSELL_ACCOUNT_RATE_LIMIT_DONT_SHOW = "go_upsell_account_rate_limit_don
 const GO_UPSELL_WINDOW = 86_400_000 // 24 hrs
 const GO_UPSELL_PROVIDERS = new Set(["opencode", "opencode-go"])

-export const GoUpsellState = Codec.struct({
-  [GO_UPSELL_FREE_TIER_LAST_SEEN_AT]: Codec.nullOr(Codec.number),
-  [GO_UPSELL_FREE_TIER_DONT_SHOW]: Codec.nullOr(Codec.number),
-  [GO_UPSELL_ACCOUNT_RATE_LIMIT_LAST_SEEN_AT]: Codec.nullOr(Codec.number),
-  [GO_UPSELL_ACCOUNT_RATE_LIMIT_DONT_SHOW]: Codec.nullOr(Codec.number),
+export const GoUpsellState = Persistence.struct({
+  [GO_UPSELL_FREE_TIER_LAST_SEEN_AT]: Schema.NullOr(Schema.Finite),
+  [GO_UPSELL_FREE_TIER_DONT_SHOW]: Schema.NullOr(Schema.Finite),
+  [GO_UPSELL_ACCOUNT_RATE_LIMIT_LAST_SEEN_AT]: Schema.NullOr(Schema.Finite),
+  [GO_UPSELL_ACCOUNT_RATE_LIMIT_DONT_SHOW]: Schema.NullOr(Schema.Finite),
 })

 function goUpsellKeys(status: SessionStatus) {
@@ -105,4 +106,3 @@ export function useUsageExceededDialogs() {
    }),
  )
 }
-
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
 import { timelinePresets } from "@opencode/session-ui/timeline/detail"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"
 import {
  settingsSchema,
  settingsPersistence,
@@ -12,9 +13,9 @@ import {
  terminalFontFamily,
 } from "./model"

-const schema = Codec.withInitial(settingsPersistence, defaultSettings)
-const decode = (input: unknown) => Codec.decodeOrThrow(schema, input)
-const encode = (value: typeof settingsSchema.Type) => schema.encode(value)
+const schema = Persistence.withInitial(settingsPersistence, defaultSettings)
+const decode = Schema.decodeUnknownSync(schema)
+const encode = Schema.encodeSync(schema)

 describe("settings timeline detail migration", () => {
  test("migrates saved switches and round trips the current settings", () => {
@@ -50,14 +51,14 @@ describe("settings schema", () => {
      general: { ...defaultSettings.general, timelineDetail: timelinePresets[4].value, autoSave: false },
      appearance: { ...defaultSettings.appearance, fontSize: 20 },
    }
-    const restore = (input: unknown) => Codec.decodeOrThrow(Codec.withInitial(settingsPersistence, initial), input)
+    const restore = Schema.decodeUnknownSync(Persistence.withInitial(settingsPersistence, initial))
    expect(restore({})).toEqual(initial)
    expect(restore({ general: { reasoningMode: "invalid", showReasoningSummaries: true } })).toEqual(initial)
    expect(restore({ general: { showReasoningSummaries: true } }).general.timelineDetail.thinking).toEqual({
      placement: "separate",
      details: "expanded",
    })
-    expect(() => Codec.decodeOrThrow(settingsSchema, {})).toThrow()
+    expect(() => Schema.decodeUnknownSync(settingsSchema)({})).toThrow()
  })

  test("supplies the existing defaults for an empty document", () => {
@@ -170,7 +171,7 @@ describe("settings schema", () => {

  test("does not silently repair invalid values during encoding", () => {
    expect(() =>
-      Codec.encodeOrThrow(settingsSchema, { ...decode({}), appearance: { fontSize: "large" } } as never),
+      Schema.encodeUnknownSync(settingsSchema)({ ...decode({}), appearance: { fontSize: "large" } }),
    ).toThrow()
  })
 })
@@ -202,6 +203,3 @@ describe("settings font families", () => {
    expect(terminalFontFamily(undefined)).toStartWith('"JetBrainsMono Nerd Font Mono", ')
  })
 })
-
-
-
@@ -5,7 +5,8 @@ import { Icon } from "@opencode/ui/icon"
 import { IconButton } from "@opencode/ui/icon-button"
 import { TextInput } from "@opencode/ui/text-input"
 import { type Component, createEffect, For, on, onCleanup, Show } from "solid-js"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"
 import { useLanguage } from "@/runtime/i18n/language"
 import { useModels } from "@/providers/models/models"
 import { useServerSDK } from "@/runtime/server/client"
@@ -19,8 +20,8 @@ type ModelItem = ReturnType<ReturnType<typeof useModels>["list"]>[number]

 const PROVIDER_ICON_SIZE = 16

-export const ModelProvidersSchema = Codec.struct({
-  collapsed: Codec.lenientRecord(Codec.fallback(Codec.boolean, () => false)),
+export const ModelProvidersSchema = Schema.Struct({
+  collapsed: Persistence.record(Persistence.fallback(Schema.Boolean, () => false)),
 })

 export const SettingsModels: Component<{ active?: boolean; autofocus?: boolean }> = (props) => {
@@ -210,4 +211,3 @@ export const SettingsModels: Component<{ active?: boolean; autofocus?: boolean }
    </>
  )
 }
-
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
 import {
  activeCommandRegistrations,
  addCommandRegistration,
@@ -10,12 +10,12 @@ import {
 } from "./command"

 test("command catalog persistence validates metadata and omits executable fields", () => {
-  const decode = ((input: unknown) => Codec.decodeOrThrow(CommandCatalog, input))
+  const decode = Schema.decodeUnknownSync(CommandCatalog)
  const catalog = decode({ open: { title: "Open", keybind: "mod+o", hidden: false, onSelect: "invalid" } })
  expect(catalog).toEqual({ open: { title: "Open", keybind: "mod+o", hidden: false } })
  expect(decode({})).toEqual({})
  expect(() => decode({ open: { title: 1 } })).toThrow()
-  expect(decode(CommandCatalog.encode(catalog))).toEqual(catalog)
+  expect(decode(Schema.encodeSync(CommandCatalog)(catalog))).toEqual(catalog)
 })

 const paletteOptions: CommandOption[] = [
@@ -79,4 +79,3 @@ describe("resolveKeybindOption", () => {
    expect(resolveKeybindOption([fallback, contextual], new KeyboardEvent("keydown"))).toBe(fallback)
  })
 })
-
@@ -2,8 +2,8 @@ import { createSimpleContext } from "@opencode/ui/context"
 import { useDialog } from "@opencode/ui/context/dialog"
 import { type Accessor, batch, createEffect, createMemo, onCleanup, onMount } from "solid-js"
 import { createStore, reconcile } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
-
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"
 import { makeEventListener } from "@solid-primitives/event-listener"
 import { useLanguage } from "@/runtime/i18n/language"
 import { useSettings } from "@/settings/model"
@@ -109,16 +109,16 @@ export function resolveKeybindOption(candidates: CommandOption[] | undefined, ev

 type CommandSource = "palette" | "keybind" | "slash"

-export const CommandCatalogItem = Codec.struct({
-  title: Codec.string,
-  description: Codec.optional(Codec.string),
-  category: Codec.optional(Codec.string),
-  keybind: Codec.optional(Codec.string),
-  slash: Codec.optional(Codec.string),
-  hidden: Codec.optional(Codec.boolean),
+export const CommandCatalogItem = Persistence.struct({
+  title: Schema.String,
+  description: Schema.optional(Schema.String),
+  category: Schema.optional(Schema.String),
+  keybind: Schema.optional(Schema.String),
+  slash: Schema.optional(Schema.String),
+  hidden: Schema.optional(Schema.Boolean),
 })
 export type CommandCatalogItem = typeof CommandCatalogItem.Type
-export const CommandCatalog = Codec.record(CommandCatalogItem)
+export const CommandCatalog = Schema.Record(Schema.String, Schema.mutableKey(CommandCatalogItem))
 export type CommandCatalog = typeof CommandCatalog.Type

 export type CommandRegistration = {
@@ -480,4 +480,3 @@ export const { use: useCommand, provider: CommandProvider } = createSimpleContex
    }
  },
 })
-
@@ -1,22 +1,23 @@
 import { expect, test } from "bun:test"
+import { Schema } from "effect"
 import type { ServerConnection } from "@/runtime/server/registry"
 import type { Tab } from "@/shell/tabs/tabs"
 import { NotificationStore, openNotificationSession, type Notification } from "./notification"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

 test("notification persistence validates and salvages individual notifications", () => {
  const valid: Notification[] = [
    { type: "turn-complete", time: 123, viewed: false, session: "session-1" },
    { type: "error", time: 124, viewed: true, error: { type: "api", message: "failed", status: 500 } },
  ]
-  const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(NotificationStore, { list: [] }), input))
+  const decode = Schema.decodeUnknownSync(Persistence.withInitial(NotificationStore, { list: [] }))
  const store = decode({
    list: [valid[0], null, { type: "unknown", time: 123, viewed: false }, { ...valid[1], error: "invalid" }, valid[1]],
  })
  expect(store.list).toEqual(valid)
  expect(decode({})).toEqual({ list: [] })
  expect(decode({ list: {} })).toEqual({ list: [] })
-  expect(decode(NotificationStore.encode(store))).toEqual(store)
+  expect(decode(Schema.encodeSync(NotificationStore)(store))).toEqual(store)
 })

 test("opens notification sessions through the tab router", () => {
@@ -40,4 +41,3 @@ test("opens notification sessions through the tab router", () => {

  expect(calls).toEqual(["add:session-1", "route:session-1", "select:session-1"])
 })
-
@@ -1,6 +1,6 @@
 import { createStore, reconcile } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
-import type { SessionError } from "@opencode/schema/session-error"
+import { Schema } from "effect"
+import { SessionError } from "@opencode/schema/session-error"
 import { type Accessor, batch, createEffect, createMemo, createRoot, getOwner, onCleanup } from "solid-js"
 import { createSimpleContext } from "@opencode/ui/context"
 import type { ServerSDK } from "@/runtime/server/client"
@@ -10,7 +10,7 @@ import { useLanguage } from "@/runtime/i18n/language"
 import { useSettings } from "@/settings/model"
 import { decode64 } from "@/runtime/persistence/base64"
 import { Persist, persisted } from "@/runtime/persistence/storage"
-
+import { Persistence } from "@/runtime/persistence/schema"
 import { playSoundById } from "@/shell/notifications/sound"
 import type { createNotificationCoordinator } from "@/shell/notifications/coordinator"
 import { useGlobal } from "@/runtime/server/runtime"
@@ -20,28 +20,19 @@ import { requireServerKey, sessionHref } from "@/shell/routes/session"
 import type { ServerScope } from "@/runtime/server/scope"
 import { useServer } from "@/runtime/server/current"

-const NotificationBase = {
-  directory: Codec.optional(Codec.string),
-  session: Codec.optional(Codec.string),
-  metadata: Codec.optional(Codec.unknown),
-  time: Codec.number,
-  viewed: Codec.boolean,
-}
-// The error payload is whatever the server reported; shape-checking it here would load the shared
-// Effect schema into the renderer's startup path for a value the server already validated.
-const StoredSessionError = Codec.make<SessionError.Error, unknown>(
-  (value) =>
-    typeof value === "object" && value !== null && "name" in value && "message" in value
-      ? (value as unknown as SessionError.Error)
-      : Codec.INVALID,
-  (value) => value,
-)
-export const Notification = Codec.union([
-  Codec.struct({ ...NotificationBase, type: Codec.literal("turn-complete") }),
-  Codec.struct({ ...NotificationBase, type: Codec.literal("error"), error: StoredSessionError }),
+const NotificationBase = {
+  directory: Schema.optional(Schema.String),
+  session: Schema.optional(Schema.String),
+  metadata: Schema.optional(Schema.Unknown),
+  time: Schema.Finite,
+  viewed: Schema.Boolean,
+}
+export const Notification = Schema.Union([
+  Persistence.struct({ ...NotificationBase, type: Schema.Literal("turn-complete") }),
+  Persistence.struct({ ...NotificationBase, type: Schema.Literal("error"), error: SessionError.Error }),
 ])
 export type Notification = typeof Notification.Type
-export const NotificationStore = Codec.struct({ list: Codec.lenientArray(Notification) })
+export const NotificationStore = Persistence.struct({ list: Persistence.array(Notification) })

 type NotificationIndex = {
  session: {
@@ -377,5 +368,3 @@ export const useNotification = () => {
  const server = useServer()
  return server.ctx.notification
 }
-
-
@@ -1,7 +1,8 @@
 import { describe, expect, test } from "bun:test"
 import { createRoot, createSignal } from "solid-js"
+import { Schema } from "effect"
 import { ServerConnection } from "@/runtime/server/registry"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"
 import { currentRoute, initialLayout, layoutPersistence, layoutSchema } from "./layout"
 import { createSessionKeyReader, ensureSessionKey, pruneSessionKeys } from "./helpers"

@@ -10,21 +11,21 @@ test("settings has its own layout route", () => {
 })

 describe("layout persistence", () => {
-  const schema = Codec.withInitial(layoutPersistence, initialLayout(ServerConnection.Key.make("local")))
-  const decode = (input: unknown) => Codec.decodeOrThrow(schema, input)
+  const schema = Persistence.withInitial(layoutPersistence, initialLayout(ServerConnection.Key.make("local")))
+  const decode = Schema.decodeUnknownSync(schema)

  test("uses supplied initial preferences after legacy migration", () => {
    const initial = initialLayout(ServerConnection.Key.make("remote"))
    initial.sidebar.width = 420
    initial.fileTree.width = 300
    initial.review.panelOpened = true
-    const restore = (input: unknown) => Codec.decodeOrThrow(Codec.withInitial(layoutPersistence, initial), input)
+    const restore = Schema.decodeUnknownSync(Persistence.withInitial(layoutPersistence, initial))
    expect(restore({})).toEqual(initial)
    expect(restore({ sidebar: { width: "bad" } }).sidebar.width).toBe(420)
    expect(restore({ fileTree: { width: 260 } }).fileTree.width).toBe(200)
    expect(restore({ fileTree: {} }).fileTree.width).toBe(300)
    expect(restore({ review: {}, fileTree: { opened: false } }).review.panelOpened).toBe(false)
-    expect(() => Codec.decodeOrThrow(layoutSchema, {})).toThrow()
+    expect(() => Schema.decodeUnknownSync(layoutSchema)({})).toThrow()
  })

  test("restores shipped defaults for missing and invalid fields", () => {
@@ -55,8 +56,8 @@ describe("layout persistence", () => {
    expect(value.sidebar).toEqual({ opened: false, width: 344, workspaces: {}, workspacesDefault: true })
    expect(value.review).toEqual({ diffStyle: "split", panelOpened: true })
    expect(value.fileTree).toEqual({ opened: true, width: 200, tab: "changes" })
-    expect(schema.encode(value)).toEqual(value)
-    expect(decode(schema.encode(value))).toEqual(value)
+    expect(Schema.encodeSync(schema)(value)).toEqual(value)
+    expect(decode(Schema.encodeSync(schema)(value))).toEqual(value)
    expect(decode({ fileTree: { opened: true } }).review.panelOpened).toBe(false)
  })

@@ -168,4 +169,3 @@ describe("pruneSessionKeys", () => {
    expect(drop).toEqual([])
  })
 })
-
@@ -1,58 +1,63 @@
 export * as TabStorage from "./schema"

-import { Codec } from "@/runtime/persistence/codec"
-import { ServerKey } from "@/runtime/server/key"
+import { Schema, SchemaGetter } from "effect"
+import { ServerKey } from "@/runtime/server/persistence"
+import { Persistence } from "@/runtime/persistence/schema"

 export { ServerKey }

-export const Session = Codec.struct({
-  type: Codec.literal("session"),
+export const Session = Persistence.struct({
+  type: Schema.Literal("session"),
  server: ServerKey,
-  sessionId: Codec.string,
-  routeSessionId: Codec.lenientOptional(Codec.string),
-  routeParentId: Codec.lenientOptional(Codec.string),
+  sessionId: Schema.String,
+  routeSessionId: Persistence.optional(Schema.String),
+  routeParentId: Persistence.optional(Schema.String),
 })

-export const Draft = Codec.struct({
-  type: Codec.literal("draft"),
-  draftID: Codec.string,
+export const Draft = Persistence.struct({
+  type: Schema.Literal("draft"),
+  draftID: Schema.String,
  server: ServerKey,
-  directory: Codec.string,
-  worktree: Codec.lenientOptional(Codec.string),
-  branch: Codec.lenientOptional(Codec.string),
-  mcp: Codec.lenientOptional(Codec.struct({ target: Codec.string, states: Codec.lenientRecord(Codec.boolean) })),
+  directory: Schema.String,
+  worktree: Persistence.optional(Schema.String),
+  branch: Persistence.optional(Schema.String),
+  mcp: Persistence.optional(Persistence.struct({ target: Schema.String, states: Persistence.record(Schema.Boolean) })),
 })

-// A stored route that only repeats the session id carries nothing; drop it and its parent.
-const SessionCodec = Codec.transform(Session, {
-  decode: (tab) => ({
-    type: tab.type,
-    server: tab.server,
-    sessionId: tab.sessionId,
-    ...(tab.routeSessionId && tab.routeSessionId !== tab.sessionId
-      ? { routeSessionId: tab.routeSessionId, ...(tab.routeParentId ? { routeParentId: tab.routeParentId } : {}) }
-      : {}),
-  }),
-  encode: (tab) => tab,
-})
-
-export const Tab = Codec.union([Session, Draft])
-export const Tabs = Codec.lenientArray(Codec.union([SessionCodec, Draft]))
-export const Recent = Codec.struct({
-  key: Codec.optional(Codec.string),
-})
-export const Info = Codec.struct({
-  title: Codec.optional(Codec.string),
-  directory: Codec.optional(Codec.string),
-})
-export const Infos = Codec.record(Info)
-export const Panes = Codec.record(
-  Codec.struct({
-    terminal: Codec.optional(Codec.boolean),
-    review: Codec.optional(Codec.boolean),
-    terminalHeight: Codec.optional(Codec.number),
-    sessionWidth: Codec.optional(Codec.number),
+const SessionCodec = Session.pipe(
+  Schema.decodeTo(Schema.toType(Session), {
+    decode: SchemaGetter.transform((tab) => ({
+      type: tab.type,
+      server: tab.server,
+      sessionId: tab.sessionId,
+      ...(tab.routeSessionId && tab.routeSessionId !== tab.sessionId
+        ? { routeSessionId: tab.routeSessionId, ...(tab.routeParentId ? { routeParentId: tab.routeParentId } : {}) }
+        : {}),
+    })),
+    encode: SchemaGetter.transform((tab) => tab),
  }),
 )
-export const ClosedTab = Codec.struct({ tab: SessionCodec, index: Codec.nonNegativeInt })
-export const Closed = Codec.lenientArray(ClosedTab)
+
+export const Tab = Schema.Union([Session, Draft])
+export const Tabs = Persistence.array(Schema.Union([SessionCodec, Draft]))
+export const Recent = Persistence.struct({
+  key: Schema.optional(Schema.String),
+})
+export const Info = Persistence.struct({
+  title: Schema.optional(Schema.String),
+  directory: Schema.optional(Schema.String),
+})
+export const Infos = Schema.Record(Schema.String, Schema.mutableKey(Info))
+export const Panes = Schema.Record(
+  Schema.String,
+  Schema.mutableKey(
+    Persistence.struct({
+      terminal: Schema.optional(Schema.Boolean),
+      review: Schema.optional(Schema.Boolean),
+      terminalHeight: Schema.optional(Schema.Finite),
+      sessionWidth: Schema.optional(Schema.Finite),
+    }),
+  ),
+)
+export const ClosedTab = Schema.Struct({ tab: SessionCodec, index: Schema.Int.check(Schema.isGreaterThanOrEqualTo(0)) })
+export const Closed = Persistence.array(ClosedTab)
@@ -3,12 +3,13 @@ import { createRoot, getOwner, onCleanup } from "solid-js"
 import { createTabMemory } from "./memory"
 import { nextTabAfterClose, pushClosedTab, removeClosedTabs, takeClosedTab, type ClosedTab } from "./closed"
 import { findSessionTab, sessionIDHasOpenTab, tabHref, tabKey, type SessionTab, type Tab } from "./tabs"
+import { Schema } from "effect"
 import { TabStorage } from "./schema"
 import type { ServerConnection } from "@/runtime/server/registry"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

 const server = "local\nhttp://localhost:4096" as ServerConnection.Key
-const decodeTabs = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(TabStorage.Tabs, []), input))
+const decodeTabs = Schema.decodeUnknownSync(Persistence.withInitial(TabStorage.Tabs, []))

 function sessionTab(sessionId: string): SessionTab {
  return { type: "session", server, sessionId }
@@ -25,7 +26,7 @@ describe("tab migration", () => {
    }
    const restored = decodeTabs([legacy, draft])
    expect(restored).toEqual([legacy, draft])
-    expect(decodeTabs(TabStorage.Tabs.encode(restored))).toEqual([legacy, draft])
+    expect(decodeTabs(Schema.encodeSync(TabStorage.Tabs)(restored))).toEqual([legacy, draft])
  })

  test("drops null and malformed persisted tabs", () => {
@@ -63,13 +64,13 @@ describe("tab migration", () => {
      draft,
    ])
    expect(tabs).toEqual([sessionTab("root"), draft])
-    expect(TabStorage.Tabs.encode(tabs)).toEqual(tabs)
-    expect(decodeTabs(TabStorage.Tabs.encode(tabs))).toEqual(tabs)
+    expect(Schema.encodeSync(TabStorage.Tabs)(tabs)).toEqual(tabs)
+    expect(decodeTabs(Schema.encodeSync(TabStorage.Tabs)(tabs))).toEqual(tabs)
  })

  test("salvages valid closed session tabs", () => {
    expect(
-      ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(TabStorage.Closed, []), input))([
+      Schema.decodeUnknownSync(Persistence.withInitial(TabStorage.Closed, []))([
        { tab: sessionTab("a"), index: 1 },
        { tab: sessionTab("b"), index: -1 },
        { tab: { type: "draft", server, draftID: "d", directory: "/project" }, index: 0 },
@@ -80,16 +81,16 @@ describe("tab migration", () => {

  test("validates auxiliary tab state", () => {
    expect(
-      ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(TabStorage.Recent, { key: undefined }), input))({ key: 1 }),
+      Schema.decodeUnknownSync(Persistence.withInitial(TabStorage.Recent, { key: undefined }))({ key: 1 }),
    ).toEqual({ key: undefined })
-    expect(Codec.decodeOrThrow(TabStorage.Infos, {})).toEqual({})
-    expect(Codec.decodeOrThrow(TabStorage.Panes, {})).toEqual({})
-    expect(Codec.decodeOrThrow(TabStorage.Infos, { tab: { title: "Title", directory: "/project" } })).toEqual({
+    expect(Schema.decodeUnknownSync(TabStorage.Infos)({})).toEqual({})
+    expect(Schema.decodeUnknownSync(TabStorage.Panes)({})).toEqual({})
+    expect(Schema.decodeUnknownSync(TabStorage.Infos)({ tab: { title: "Title", directory: "/project" } })).toEqual({
      tab: { title: "Title", directory: "/project" },
    })
-    const panes = Codec.decodeOrThrow(TabStorage.Panes, { tab: { terminal: true, terminalHeight: 300 } })
-    expect(TabStorage.Panes.encode(panes)).toEqual({ tab: { terminal: true, terminalHeight: 300 } })
-    expect(() => Codec.decodeOrThrow(TabStorage.Panes, { tab: { terminal: "yes" } })).toThrow()
+    const panes = Schema.decodeUnknownSync(TabStorage.Panes)({ tab: { terminal: true, terminalHeight: 300 } })
+    expect(Schema.encodeSync(TabStorage.Panes)(panes)).toEqual({ tab: { terminal: true, terminalHeight: 300 } })
+    expect(() => Schema.decodeUnknownSync(TabStorage.Panes)({ tab: { terminal: "yes" } })).toThrow()
  })
 })

@@ -208,5 +209,3 @@ describe("closed tab stack", () => {
    expect(nextTabAfterClose([sessionTab("a")], 0, true)).toBeNull()
  })
 })
-
-
@@ -9,7 +9,8 @@
  justify-content: center;
 }

-[data-titlebar-tab] {
+[data-titlebar-tab],
+[data-titlebar-tab-action] {
  --tab-base: var(--v2-background-bg-deep);
  --tab-overlay: transparent;
  background: linear-gradient(var(--tab-overlay), var(--tab-overlay)), var(--tab-base);
@@ -68,6 +69,14 @@
  --tab-overlay: var(--v2-overlay-simple-overlay-pressed);
 }

+[data-titlebar-tab-action]:is(:hover, :focus-visible) {
+  --tab-overlay: var(--v2-overlay-simple-overlay-hover);
+}
+
+[data-titlebar-tab-action]:is(:active, [data-state="pressed"]) {
+  --tab-overlay: var(--v2-overlay-simple-overlay-pressed);
+}
+
 [data-titlebar-tab]:is(:hover, [data-state="pressed"]) [data-slot="tab-close"] {
  background: linear-gradient(var(--tab-overlay), var(--tab-overlay)), var(--tab-base);
 }
@@ -351,9 +351,10 @@ export function Titlebar(props: {
              >
                <button
                  type="button"
+                  data-titlebar-tab-action
                  data-action="vertical-tabs-home"
                  data-state={layout.route().type === "home" ? "pressed" : undefined}
-                  class="group mb-1 flex h-7 w-full shrink-0 items-center gap-1.5 rounded-[6px] ps-1.5 pe-2 text-[13px] leading-4 text-v2-text-text-faint hover:bg-v2-background-bg-layer-02 hover:text-v2-text-text-base data-[state=pressed]:bg-v2-background-bg-layer-02 data-[state=pressed]:text-v2-text-text-base"
+                  class="group mb-1 flex h-7 w-full shrink-0 items-center gap-1.5 rounded-[6px] ps-1.5 pe-2 text-[13px] leading-4 text-v2-text-text-faint hover:text-v2-text-text-base data-[state=pressed]:text-v2-text-text-base"
                  onClick={toggleHome}
                  aria-label={language.t("home.title")}
                  aria-pressed={layout.route().type === "home"}
@@ -650,8 +651,9 @@ export function Titlebar(props: {
                            {homeButton(true)}
                            <button
                              type="button"
+                              data-titlebar-tab-action
                              data-action="vertical-tabs-new-session"
-                              class="group flex h-7 w-full shrink-0 items-center gap-1.5 rounded-[6px] ps-1.5 pe-2 text-[13px] leading-4 text-v2-text-text-faint hover:bg-v2-background-bg-layer-02 hover:text-v2-text-text-base"
+                              class="group flex h-7 w-full shrink-0 items-center gap-1.5 rounded-[6px] ps-1.5 pe-2 text-[13px] leading-4 text-v2-text-text-faint hover:text-v2-text-text-base"
                              onClick={openNewTab}
                              aria-label={language.t("command.session.new")}
                            >
@@ -1,13 +1,13 @@
 import { expect, test } from "bun:test"
+import { Schema } from "effect"
 import { HighlightsStore } from "./highlights"
-import { Codec } from "@/runtime/persistence/codec"
+import { Persistence } from "@/runtime/persistence/schema"

 test("highlight persistence defaults missing or invalid versions and round-trips valid versions", () => {
-  const decode = ((input: unknown) => Codec.decodeOrThrow(Codec.withInitial(HighlightsStore, { version: undefined }), input))
+  const decode = Schema.decodeUnknownSync(Persistence.withInitial(HighlightsStore, { version: undefined }))
  expect(decode({})).toEqual({ version: undefined })
  expect(decode({ version: null })).toEqual({ version: undefined })
  const value = decode({ version: "1.2.3", legacy: true })
  expect(value).toEqual({ version: "1.2.3" })
-  expect(HighlightsStore.encode(value)).toEqual(value)
+  expect(Schema.encodeSync(HighlightsStore)(value)).toEqual(value)
 })
-
@@ -1,18 +1,18 @@
 import { createEffect, onCleanup } from "solid-js"
 import { createStore } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
 import { createSimpleContext } from "@opencode/ui/context"
 import { useDialog } from "@opencode/ui/context/dialog"
 import { usePlatform } from "@/runtime/platform/platform"
 import { useSettings } from "@/settings/model"
 import { persisted } from "@/runtime/persistence/storage"
-
+import { Persistence } from "@/runtime/persistence/schema"
 import { DialogReleaseNotes, type Highlight } from "@/shell/updates/release-notes"

 const CHANGELOG_URL = "https://opencode.ai/changelog.json"

-export const HighlightsStore = Codec.struct({
-  version: Codec.undefinedOr(Codec.string),
+export const HighlightsStore = Persistence.struct({
+  version: Schema.UndefinedOr(Schema.String),
 })

 type ParsedRelease = {
@@ -233,4 +233,3 @@ export const { use: useHighlights, provider: HighlightsProvider } = createSimple
    }
  },
 })
-
@@ -1,19 +1,20 @@
 import type { FileContent } from "@/runtime/server/types"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
+import { Persistence } from "@/runtime/persistence/schema"

-export const FileSelection = Codec.struct({
-  startLine: Codec.number,
-  startChar: Codec.number,
-  endLine: Codec.number,
-  endChar: Codec.number,
+export const FileSelection = Persistence.struct({
+  startLine: Schema.Number,
+  startChar: Schema.Number,
+  endLine: Schema.Number,
+  endChar: Schema.Number,
 })
 export type FileSelection = typeof FileSelection.Type

-export const SelectedLineRange = Codec.struct({
-  start: Codec.number,
-  end: Codec.number,
-  side: Codec.lenientOptional(Codec.literals(["additions", "deletions"])),
-  endSide: Codec.lenientOptional(Codec.literals(["additions", "deletions"])),
+export const SelectedLineRange = Persistence.struct({
+  start: Schema.Number,
+  end: Schema.Number,
+  side: Persistence.optional(Schema.Literals(["additions", "deletions"])),
+  endSide: Persistence.optional(Schema.Literals(["additions", "deletions"])),
 })
 export type SelectedLineRange = typeof SelectedLineRange.Type

@@ -43,4 +44,3 @@ export function selectionFromLines(range: SelectedLineRange): FileSelection {
    endChar: 0,
  }
 }
-
@@ -1,7 +1,8 @@
 import { createEffect, createRoot } from "solid-js"
 import { produce } from "solid-js/store"
-import { Codec } from "@/runtime/persistence/codec"
+import { Schema } from "effect"
 import { Persist, persisted } from "@/runtime/persistence/storage"
+import { Persistence } from "@/runtime/persistence/schema"
 import { createScopedCache } from "@/runtime/server/scoped-cache"
 import { SelectedLineRange } from "./types"
 import type { ServerScope } from "@/runtime/server/scope"
@@ -10,14 +11,14 @@ const WORKSPACE_KEY = "__workspace__"
 const MAX_FILE_VIEW_SESSIONS = 20
 const MAX_VIEW_FILES = 500

-const FileViewSchema = Codec.struct({
-  scrollTop: Codec.lenientOptional(Codec.number),
-  scrollLeft: Codec.lenientOptional(Codec.number),
-  selectedLines: Codec.lenientOptional(Codec.nullOr(SelectedLineRange)),
+const FileViewSchema = Persistence.struct({
+  scrollTop: Persistence.optional(Schema.Finite),
+  scrollLeft: Persistence.optional(Schema.Finite),
+  selectedLines: Persistence.optional(Schema.NullOr(SelectedLineRange)),
 })

-export const FileViewsSchema = Codec.struct({
-  file: Codec.lenientRecord(Codec.fallback(FileViewSchema, () => ({}))),
+export const FileViewsSchema = Schema.Struct({
+  file: Persistence.record(Persistence.fallback(FileViewSchema, () => ({}))),
 })

 function normalizeSelectedLines(range: SelectedLineRange): SelectedLineRange {
@@ -149,4 +150,3 @@ export function createFileViewCache(scope: ServerScope) {
    clear: () => cache.clear(),
  }
 }
-
@@ -1,7 +1,7 @@
 {
  "$schema": "https://json.schemastore.org/package.json",
  "name": "@opencode/cli",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "type": "module",
  "license": "MIT",
  "bin": {
@@ -1,7 +1,7 @@
 {
  "$schema": "https://json.schemastore.org/package.json",
  "name": "@opencode/client",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "type": "module",
  "license": "MIT",
  "repository": {
@@ -6,6 +6,8 @@
 - Tool schemas are the model-facing Interface. Keep arguments minimal and natural to the operation; never add unrelated IDs as ambient capability tokens.
 - State model-visible diagnostics, logs, tool descriptions, and instructions directly. The execution context is already clear; do not repeat `Code Mode` or `CodeMode` unless the distinction is necessary.
 - When interpreter behavior or support changes, update `interpreter-support.md` and direct tests in the same PR.
+- Program values are `Value` (`src/interpreter/objects.ts`); host values are `unknown` and are copied in at the boundaries (`fromHost`, `fromJson`). Do not widen program-facing signatures back to `unknown`.
+- A built-in kind of object is one `Obj` subclass (`Wrapper` for host-backed data such as Date or Map, `Opaque` for machinery such as functions and promises) that overrides `tag`, `toString`, `toPrimitive`, `inspect`, `toHost`, and `iterator` as needed. Do not add `instanceof` ladders over the built-in classes elsewhere; ask the object.

 ## OpenAPI

@@ -180,7 +180,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
      on any other value throws a catchable `TypeError` naming the callee: other built-in functions such as `Number`
      say `new` is unsupported and point at the plain call, user-defined functions report the constructor gap below,
      and non-callable values are not constructors. Error constructors take the ES2022 options object, so
-      `new Error(message, { cause })` installs a non-enumerable `cause` when the option is present.
+      `new Error(message, { cause })` installs a non-enumerable `cause` when the option is present. `Error.isError`
+      is true for every Error value.
 - [x] Arithmetic operators: `+`, `-`, `*`, `/`, `%`, and `**`.
 - [x] Equality and ordering: `==`, `!=`, `===`, `!==`, `<`, `<=`, `>`, and `>=`.
 - [x] Bitwise operators: `&`, `|`, `^`, `~`, `<<`, `>>`, and `>>>`.
@@ -270,8 +271,9 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [x] `Object.is` for supported data values.
 - [x] `Object.groupBy` over finite collections and custom synchronous iterators/generators, with string-key coercion
      and plain-object results.
- [x] `Object.prototype` methods on values: `toString` (`"[object Array]"`), `toLocaleString`, `valueOf`,
-      `hasOwnProperty`, `isPrototypeOf`, and `propertyIsEnumerable`.
+- [x] `Object.prototype` methods on values: `toString` (`"[object Array]"`, `"[object Map]"`, `"[object Promise]"`, and so
+      on for every built-in kind, as JS reports through `Symbol.toStringTag`), `toLocaleString` (calls the value's
+      `toString`, as in JS), `valueOf`, `hasOwnProperty`, `isPrototypeOf`, and `propertyIsEnumerable`.

 ## Arrays

@@ -285,7 +287,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
      `lastIndexOf`.
 - [x] Aggregation: `reduce` and `reduceRight`.
 - [x] Ordering: `sort`, `toSorted`, `reverse`, and `toReversed`.
- [x] Access/copying: `at`, `slice`, `concat`, `flat`, `with`, and `join`.
+- [x] Access/copying: `at`, `slice`, `concat`, `flat`, `with`, `join`, and `toLocaleString` (each element's
+      `toLocaleString`, holes and nullish elements as empty strings).
 - [x] Mutation: `push`, `pop`, `shift`, `unshift`, `splice`, `fill`, and `copyWithin`.
 - [x] `keys`, `values`, `entries`, and `[Symbol.iterator]` (the same function as `values`) return live iterator objects
      with `next()` and `[Symbol.iterator]`, as in JS. Iterator objects are opaque references: they print as
@@ -308,7 +311,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262

 ## Strings

- [x] Case/normalization: `toLowerCase`, `toUpperCase`, `normalize`.
+- [x] Case/normalization: `toLowerCase`, `toUpperCase`, `normalize`, and the `toLocaleLowerCase`/`toLocaleUpperCase`
+      aliases, which ignore their locale argument and apply the default Unicode casing.
 - [x] Trimming: `trim`, `trimStart`, and `trimEnd`, plus the Annex B `trimLeft` and `trimRight` aliases.
 - [x] Searching/tests: `includes`, `startsWith`, `endsWith`, `indexOf`, `lastIndexOf`, and `search`.
 - [x] Slicing/access: `slice`, `substring`, Annex B `substr`, `at`, `charAt`, `charCodeAt`, and `codePointAt`.
@@ -332,7 +336,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [x] Coercion functions: `Number`, `parseInt`, and `parseFloat`.
 - [x] Number predicates/parsers: `Number.isInteger`, `Number.isFinite`, `Number.isNaN`, `Number.isSafeInteger`,
      `Number.parseInt`, and `Number.parseFloat`.
- [x] Number formatting: `toFixed`, `toPrecision`, `toExponential`, `toString`, and `valueOf`.
+- [x] Number formatting: `toFixed`, `toPrecision`, `toExponential`, `toString`, `valueOf`, and `toLocaleString`, which
+      always formats as `en-US` (`"1,234.5"`) so output does not depend on the host.
 - [x] Number constants: `MAX_SAFE_INTEGER`, `MIN_SAFE_INTEGER`, `MAX_VALUE`, `MIN_VALUE`, `EPSILON`, `NaN`,
      `POSITIVE_INFINITY`, and `NEGATIVE_INFINITY`.
 - [x] Math constants: `PI`, `E`, `LN2`, `LN10`, `LOG2E`, `LOG10E`, `SQRT2`, and `SQRT1_2`.
@@ -379,6 +384,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
      `TimeClip` behavior.
 - [x] `Date.prototype.toUTCString` and its `toGMTString` alias.
 - [x] `toDateString` and `toTimeString` in the host's local timezone.
+- [x] `toLocaleString`, `toLocaleDateString`, and `toLocaleTimeString` always format as `en-US` in UTC
+      (`"1/1/1970, 12:00:00 AM"`) so output does not depend on the host.
 - [x] Native one-argument Date coercion for supported values, including booleans, null, arrays, and plain objects.
 - [ ] Date setters and multi-argument construction coerce object arguments through `valueOf`/`toString` and surface
      their throws.
@@ -404,7 +411,7 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262

 - [x] Static `Map.groupBy` over finite collections and custom synchronous iterators/generators, preserving key identity.
 - [x] `new Map()` from synchronous iterables of entries.
- [x] Map `get`, `set`, `has`, `delete`, `clear`, `size`, and `forEach`.
+- [x] Map `get`, `set`, `has`, `delete`, `clear`, `size`, `forEach`, `getOrInsert`, and `getOrInsertComputed`.
 - [x] `new Set()` from synchronous iterables.
 - [x] Set `add`, `has`, `delete`, `clear`, `size`, and `forEach`.
 - [x] Live `keys`, `values`, `entries`, and `[Symbol.iterator]` iterators for Map and Set; a Set-like operand's `keys()`
@@ -1,7 +1,7 @@
 {
  "$schema": "https://json.schemastore.org/package.json",
  "name": "@opencode/codemode",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "description": "Effect-native confined code execution over schema-described tools",
  "type": "module",
  "license": "MIT",
@@ -15,6 +15,7 @@ import {
  Obj,
  PromiseObj,
  record,
+  type Value,
  SetObj,
  URLSearchParamsObj,
  HeadersObj,
@@ -23,14 +24,14 @@ import { typeofValue } from "./interpreter/references.js"

 export type Json = Schema.Json

-type Replacer<R> = (args: Array<unknown>) => Effect.Effect<unknown, unknown, R>
+type Replacer<R> = (args: Array<Value>) => Effect.Effect<Value, unknown, R>

 /**
 * What `JSON.stringify` would serialize for a program value, as host JSON: `toJSON` is honored, functions and
 * `undefined` vanish, non-finite numbers become null, and everything else is copied. Two departures from JS
 * so a mistake is not a silent `{}`: an Error serializes as `{ name, message, ...own }`, and a promise throws.
 */
-export const toJson = <R>(ctx: Interpreter<R>, value: unknown, replacer?: Replacer<R>) =>
+export const toJson = <R>(ctx: Interpreter<R>, value: Value, replacer?: Replacer<R>) =>
  walk(ctx, value, replacer, false)

 /**
@@ -38,11 +39,11 @@ export const toJson = <R>(ctx: Interpreter<R>, value: unknown, replacer?: Replac
 * awaited, a Set crosses as an array, a URLSearchParams as its query string, a Uint8Array asks to be encoded as
 * text first, and a `__proto__` key is dropped so host code can never receive one.
 */
-export const toBoundary = <R>(ctx: Interpreter<R>, value: unknown) => walk(ctx, value, undefined, true)
+export const toBoundary = <R>(ctx: Interpreter<R>, value: Value) => walk(ctx, value, undefined, true)

 const walk = <R>(
  ctx: Interpreter<R>,
-  value: unknown,
+  value: Value,
  replacer: Replacer<R> | undefined,
  boundary: boolean,
 ): Effect.Effect<Json | undefined, unknown, R> => {
@@ -104,7 +105,7 @@ const walk = <R>(
 }

 /** Host JSON as program values: objects and arrays are copied, primitives pass through. */
-export const fromJson = <R>(ctx: Interpreter<R>, value: unknown): unknown => {
+export const fromJson = <R>(ctx: Interpreter<R>, value: Json | undefined): Value => {
  if (value === null || typeof value !== "object") return value
  if (Array.isArray(value))
    return new Arr(
@@ -1,12 +1,12 @@
 import { Effect, Exit } from "effect"
-import { coerceToNumber, coerceToString } from "../stdlib/value.js"
 import type { Interpreter } from "./interpreter.js"
+import { primitivePrototype } from "./intrinsics.js"
 import { typeError } from "./model.js"
-import { Callable, get, Native, DateObj, Obj } from "./objects.js"
+import { Callable, get, Native, DateObj, Obj, coerceToNumber, coerceToString, type Value } from "./objects.js"
 import { typeofValue } from "./references.js"

 export type IteratorCursor<R> = {
-  readonly next: Effect.Effect<{ readonly done: boolean; readonly value: unknown }, unknown, R>
+  readonly next: Effect.Effect<{ readonly done: boolean; readonly value: Value }, unknown, R>
  readonly close: Effect.Effect<void, unknown, R>
 }

@@ -26,9 +26,9 @@ export const preserveConsumerError = <A, R>(
 */
 export const toPrimitive = <R>(
  ctx: Interpreter<R>,
-  value: unknown,
+  value: Value,
  hint: "number" | "string" | "default",
-): Effect.Effect<unknown, unknown, R> => {
+): Effect.Effect<Value, unknown, R> => {
  if (!(value instanceof Obj)) return Effect.succeed(value)
  const asString = hint === "string" || (hint === "default" && value instanceof DateObj)
  const order = asString ? ["toString", "valueOf"] : ["valueOf", "toString"]
@@ -43,24 +43,31 @@ export const toPrimitive = <R>(
  })
 }

-export const toPrimitiveString = <R>(ctx: Interpreter<R>, value: unknown) =>
+/** Invoke(value, name): calls the method the value would find through its prototype. */
+export const invoke = <R>(ctx: Interpreter<R>, value: Value, name: string, label: string) => {
+  const target = value instanceof Obj ? value : primitivePrototype(ctx.builtins, value)
+  if (target === undefined) throw typeError(`${label} called on null or undefined.`)
+  return ctx.call(get(target, name), value, [])
+}
+
+export const toPrimitiveString = <R>(ctx: Interpreter<R>, value: Value) =>
  Effect.map(toPrimitive(ctx, value, "string"), coerceToString)

-export const toPrimitiveNumber = <R>(ctx: Interpreter<R>, value: unknown) =>
+export const toPrimitiveNumber = <R>(ctx: Interpreter<R>, value: Value) =>
  Effect.map(toPrimitive(ctx, value, "number"), coerceToNumber)

 // The single acceptance list for callbacks: collections, sort, string replacers,
 // Array.from mappers, and promise reactions all admit exactly these callables.
 // Admission means dispatchable, not necessarily invocable: new-requiring
 // constructors pass the gate and throw a TypeError on call, like JS.
-export const isSupportedCallback = (value: unknown): value is Callable =>
+export const isSupportedCallback = (value: Value): value is Callable =>
  value instanceof Callable && !(value instanceof Native && !value.callback)

 export const applyCollectionCallback = <R>(
  ctx: Interpreter<R>,
-  callback: unknown,
+  callback: Value,
  name: string,
-): ((args: Array<unknown>) => Effect.Effect<unknown, unknown, R>) => {
+): ((args: Array<Value>) => Effect.Effect<Value, unknown, R>) => {
  if (!isSupportedCallback(callback)) {
    if (typeofValue(callback) === "function") {
      throw typeError(
@@ -6,10 +6,21 @@ import { type AstNode, formatLocation, PendingThrow, Throw, sourceLocation, type
 import { containsRuntimeReference } from "./references.js"
 import { createErrorValue, type ErrorType, isErrorType } from "./intrinsics.js"
 import { constructor, methods, prototypeFrom, receiver } from "./native.js"
-import { type Callable, define, get, has, hidden, type Native, Arr, ErrorObj, Obj } from "./objects.js"
+import {
+  type Callable,
+  define,
+  get,
+  has,
+  hidden,
+  type Native,
+  Arr,
+  ErrorObj,
+  Obj,
+  coerceToString,
+  type Value,
+} from "./objects.js"
 import type { Interpreter } from "./interpreter.js"
 import { formatValue } from "../stdlib/console.js"
-import { coerceToString } from "../stdlib/value.js"

 export const normalizeError = (error: unknown): Diagnostic => {
  if (error instanceof PendingThrow) {
@@ -86,7 +97,7 @@ export const locate = (error: unknown, node?: AstNode): unknown => {
 }

 /** The program value a handler receives for a failure; one failure always yields the same value. */
-export const materialize = <R>(ctx: Interpreter<R>, thrown: unknown): unknown => {
+export const materialize = <R>(ctx: Interpreter<R>, thrown: unknown): Value => {
  if (thrown instanceof Throw) return thrown.value
  const builtins = ctx.builtins
  if (thrown instanceof PendingThrow) {
@@ -113,7 +124,7 @@ const errorToString = (self: Obj): string => {

 export const createAggregateErrorValue = <R>(
  ctx: Interpreter<R>,
-  errors: Array<unknown>,
+  errors: Array<Value>,
  message: string,
  proto: Obj = ctx.builtins.AggregateError,
 ) => {
@@ -124,13 +135,13 @@ export const createAggregateErrorValue = <R>(

 const constructAggregateErrorValue = <R>(
  ctx: Interpreter<R>,
-  args: Array<unknown>,
+  args: Array<Value>,
  proto: Obj,
 ): Effect.Effect<ErrorObj, unknown, R> =>
  Effect.gen(function* () {
    const cursor = yield* ctx.iterate(args[0])
    if (cursor === undefined) throw typeError("new AggregateError(...) expects a synchronous iterable of errors.")
-    const errors: Array<unknown> = []
+    const errors: Array<Value> = []
    while (true) {
      const step = yield* cursor.next
      if (step.done) {
@@ -144,7 +155,7 @@ const constructAggregateErrorValue = <R>(
 export const errorGlobal = <R>(type: ErrorType, ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
  const prototype = builtins[type]
-  const construct = (args: Array<unknown>, newTarget: Callable) => {
+  const construct = (args: Array<Value>, newTarget: Callable) => {
    const proto = prototypeFrom(newTarget, prototype)
    const created =
      type === "AggregateError"
@@ -168,6 +179,7 @@ export const errorGlobal = <R>(type: ErrorType, ctx: Interpreter<R>) => {
    methods(builtins, prototype, [
      ["toString", 0, (thisValue) => errorToString(receiver(Obj, thisValue, "Error.prototype.toString"))],
    ])
+    methods(builtins, ctor, [["isError", 1, (_, args) => args[0] instanceof ErrorObj]])
  }
  return ctor
 }
@@ -4,6 +4,7 @@ import type { DataValue, Diagnostic, ResolvedExecutionLimits, Result } from "../
 import { toBoundary } from "../data.js"
 import { ToolRuntime } from "../tool-runtime.js"
 import { normalizeError } from "./errors.js"
+import type { Value } from "./objects.js"
 import { createBuiltins } from "./intrinsics.js"
 import { Pending } from "./promises.js"
 import { Interpreter } from "./interpreter.js"
@@ -13,7 +14,7 @@ export const executeProgram = <R>(
  prepared: ToolRuntime.Prepared<R>,
  limits: ResolvedExecutionLimits,
  hooks: ToolRuntime.Hooks<R>,
-  globals?: (ctx: Interpreter<R>) => ReadonlyArray<readonly [string, unknown]>,
+  globals?: (ctx: Interpreter<R>) => ReadonlyArray<readonly [string, Value]>,
 ): Effect.Effect<Result, never, R> => {
  if (code.trim().length === 0) {
    return Effect.succeed({
@@ -1,6 +1,5 @@
 import { Effect } from "effect"
 import type { Extension } from "../extension.js"
-import { coerceToString } from "../stdlib/value.js"
 import { type ExtensionInvocation, hooked } from "../tool-runtime.js"
 import type { Interpreter } from "./interpreter.js"
 import { createErrorValue, isErrorType } from "./intrinsics.js"
@@ -8,9 +7,7 @@ import { MAX_VALUE_DEPTH } from "./limits.js"
 import { PendingThrow, Throw, typeError } from "./model.js"
 import { fn } from "./native.js"
 import {
-  Callable,
  define,
-  entries,
  get,
  has,
  hidden,
@@ -19,18 +16,17 @@ import {
  Bytes,
  DateObj,
  ErrorObj,
-  GeneratorObj,
-  IteratorObj,
+  HeadersObj,
  MapObj,
  Obj,
-  PromiseObj,
  RegExpObj,
  SetObj,
  URLObj,
  URLSearchParamsObj,
-  HeadersObj,
+  coerceToString,
+  type Value,
 } from "./objects.js"
-import { describeValue } from "./references.js"
+import { describeValue, isOpaque } from "./references.js"

 /**
 * The global bindings of one run's extensions. Everything crossing the boundary is converted: plain data and
@@ -40,35 +36,18 @@ import { describeValue } from "./references.js"
 export const extensionGlobals = <R>(
  ctx: Interpreter<R>,
  extensions: ReadonlyArray<Extension>,
-): ReadonlyArray<readonly [string, unknown]> => {
+): ReadonlyArray<readonly [string, Value]> => {
  const builtins = ctx.builtins

-  const toHost = (value: unknown, label: string, depth = 0, seen = new Set<object>()): unknown => {
+  const toHost = (value: Value, label: string, depth = 0, seen = new Set<object>()): unknown => {
    if (depth > MAX_VALUE_DEPTH) throw typeError(`${label} exceeds the maximum value depth of ${MAX_VALUE_DEPTH}.`)
-    if (value === null || typeof value !== "object") {
-      if (isPrimitive(value)) return value
-      throw typeError(`${label} contains ${describeValue(value)}, which cannot be passed to an extension.`)
-    }
-    if (value instanceof Bytes) return new Uint8Array(value.bytes)
-    if (value instanceof DateObj) return new Date(value.time)
-    if (value instanceof RegExpObj) return new RegExp(value.regex.source, value.regex.flags)
-    if (value instanceof URLObj) return new URL(value.url.href)
-    if (value instanceof URLSearchParamsObj) return new URLSearchParams(value.params)
-    if (value instanceof HeadersObj) return new Headers(value.headers)
-    const next = (item: unknown) => toHost(item, label, depth + 1, seen)
-    if (value instanceof MapObj) return new Map([...value.map].map(([key, item]) => [next(key), next(item)]))
-    if (value instanceof SetObj) return new Set([...value.set].map(next))
-    if (
-      !(value instanceof Obj) ||
-      value instanceof Callable ||
-      value instanceof GeneratorObj ||
-      value instanceof IteratorObj ||
-      value instanceof PromiseObj
-    ) {
+    if (isPrimitive(value)) return value
+    if (!(value instanceof Obj) || isOpaque(value)) {
      throw typeError(`${label} contains ${describeValue(value)}, which cannot be passed to an extension.`)
    }
    if (seen.has(value)) throw typeError(`${label} contains a circular value.`)
    seen.add(value)
+    const next = (item: Value) => toHost(item, label, depth + 1, seen)
    if (value instanceof ErrorObj) {
      const name = coerceToString(get(value, "name"))
      const message = get(value, "message")
@@ -89,19 +68,12 @@ export const extensionGlobals = <R>(
      seen.delete(value)
      return copied
    }
-    const copied =
-      value instanceof Arr
-        ? value.items.map(next)
-        : Object.fromEntries(
-            entries(value)
-              .filter(([key]) => key !== "__proto__")
-              .map(([key, item]) => [key, next(item)]),
-          )
+    const copied = value.toHost(next)
    seen.delete(value)
    return copied
  }

-  const fromHost = (value: unknown, label: string, depth = 0, seen = new Set<object>()): unknown => {
+  const fromHost = (value: unknown, label: string, depth = 0, seen = new Set<object>()): Value => {
    if (depth > MAX_VALUE_DEPTH) throw typeError(`${label} exceeds the maximum value depth of ${MAX_VALUE_DEPTH}.`)
    if (isPrimitive(value)) return value
    if (typeof value === "function") return wrap(value, label)
@@ -200,7 +172,7 @@ export const extensionGlobals = <R>(
 */
 const uncrossed = new Set(["stack", "constructor", "toString", "__proto__"])
 const left = Symbol("left behind")
-const crossing = (convert: () => unknown): unknown => {
+const crossing = <T>(convert: () => T): T | typeof left => {
  try {
    return convert()
  } catch (reason) {
@@ -219,7 +191,7 @@ const hostErrors = new Map<string, ErrorConstructor>([
 ])

 // The primitives the interpreter operates on; symbols and BigInts are not among them.
-const isPrimitive = (value: unknown): boolean =>
+const isPrimitive = (value: unknown): value is string | number | boolean | null | undefined =>
  value === null ||
  value === undefined ||
  typeof value === "string" ||
@@ -1,7 +1,7 @@
 import { Effect } from "effect"
 import { fn, type Method, methods, receiver } from "./native.js"
 import { AsyncIteratorSymbol, type GeneratorRequestKind, IteratorSymbol } from "./model.js"
-import { define, hidden, GeneratorObj } from "./objects.js"
+import { define, hidden, GeneratorObj, type Value } from "./objects.js"
 import type { Interpreter } from "./interpreter.js"

 /** `next`/`return`/`throw` on the generator prototypes; async generators answer with promises. */
@@ -13,9 +13,9 @@ export const generatorGlobals = <R>(ctx: Interpreter<R>): void => {
    const request = (kind: GeneratorRequestKind): Method => [
      kind,
      1,
-      (thisValue: unknown, args: Array<unknown>) => {
+      (thisValue: Value, args: Array<Value>) => {
        const generator = receiver(GeneratorObj, thisValue, `${label}.prototype.${kind}`)
-        const requested = generator.request(kind, args[0]) as Effect.Effect<unknown, unknown, R>
+        const requested = generator.request(kind, args[0]) as Effect.Effect<Value, unknown, R>
        return generator.asynchronous ? ctx.pending.create(requested) : requested
      },
    ]
@@ -1,4 +1,5 @@
 import { Effect } from "effect"
+import type { Value } from "./objects.js"
 import { arrayGlobal } from "../stdlib/array.js"
 import { textDecoderGlobal, textEncoderGlobal, uint8ArrayGlobal } from "../stdlib/bytes.js"
 import { mapGlobal, setGlobal } from "../stdlib/collections.js"
@@ -51,7 +52,7 @@ const symbolGlobal = <R>(ctx: Interpreter<R>) => {
  return symbol
 }

-type Factory = <R>(ctx: Interpreter<R>) => unknown
+type Factory = <R>(ctx: Interpreter<R>) => Value

 // A table rather than a list so the names are known before any runtime exists.
 const table: Record<string, Factory> = {
@@ -100,7 +101,7 @@ const table: Record<string, Factory> = {
 export const globalNames: ReadonlySet<string> = new Set(Object.keys(table))

 /** The immutable global bindings of every program, in declaration order. */
-export const globals = <R>(ctx: Interpreter<R>): ReadonlyArray<readonly [string, unknown]> => {
+export const globals = <R>(ctx: Interpreter<R>): ReadonlyArray<readonly [string, Value]> => {
  generatorGlobals(ctx)
  iteratorGlobals(ctx)
  return Object.entries(table).map(([name, factory]) => [name, factory(ctx)] as const)
@@ -32,6 +32,7 @@ import type {
  Statement,
  Super,
  SwitchStatement,
+  Literal,
  TemplateLiteral,
  ThrowStatement,
  TryStatement,
@@ -62,7 +63,7 @@ import {
 } from "./model.js"
 import { checkStringLength } from "./limits.js"
 import { locate, materialize } from "./errors.js"
-import type { Builtins } from "./intrinsics.js"
+import { type Builtins, primitivePrototype } from "./intrinsics.js"
 import { globals } from "./globals.js"
 import {
  assign,
@@ -75,20 +76,16 @@ import {
  Native,
  parseArrayIndex,
  Arr,
-  Bytes,
-  DateObj,
  Fn,
  GeneratorObj,
-  IteratorObj,
-  MapObj,
  Obj,
  PromiseObj,
-  SetObj,
-  URLSearchParamsObj,
-  HeadersObj,
  record,
  remove,
  set,
+  coerceToNumber,
+  coerceToString,
+  type Value,
 } from "./objects.js"
 import { preserveConsumerError } from "./callback.js"
 import { Pending, resolvePromise, resolvePromiseValue } from "./promises.js"
@@ -96,7 +93,7 @@ import { containsOpaqueReference, describeValue, rejectCircularInsertion, typeof
 import { ScopeStack } from "./scope.js"
 import { constructRegExp } from "../stdlib/regexp.js"
 import { enumerableSource } from "../stdlib/object.js"
-import { coerceToNumber, coerceToString, compoundOperators } from "../stdlib/value.js"
+import { compoundOperators } from "../stdlib/value.js"

 // What a loop does with its body's result: exit with a StatementResult, or undefined to keep iterating.
 // Unlabelled break ends this loop; a label the loop does not carry propagates outward.
@@ -127,7 +124,14 @@ const calleeDescription = (callee: Expression | Super | undefined): string => {
 }

 // OrdinaryHasInstance: walk the left operand's chain looking for the constructor's `prototype`.
-const instanceofValue = (lhs: unknown, rhs: unknown, node: AstNode): boolean => {
+// acorn types every literal as possibly a BigInt or RegExp; regex literals become RegExp objects before this is asked.
+const literal = (node: Literal): Value => {
+  if (typeof node.value === "bigint") throw typeError("BigInt literals are not supported.", node)
+  if (node.value instanceof RegExp) throw unsupportedSyntax("RegExpLiteral", node)
+  return node.value
+}
+
+const instanceofValue = (lhs: Value, rhs: Value, node: AstNode): boolean => {
  if (!(rhs instanceof Callable)) {
    throw typeError("The right-hand side of 'instanceof' is not callable.", node)
  }
@@ -224,7 +228,7 @@ const loopDeclaration = (left: VariableDeclaration | Pattern, statement: "for...

 type CustomIterator = {
  iterator: Obj
-  next: unknown
+  next: Value
  asynchronous: boolean
 }

@@ -232,13 +236,13 @@ type CustomIterator = {
 type MemberReference = {
  target: Obj
  key: PropertyKey
-  receiver: unknown
+  receiver: Value
 }

 type GeneratorRequest = {
  kind: GeneratorRequestKind
-  value: unknown
-  response: Deferred.Deferred<unknown, unknown>
+  value: Value
+  response: Deferred.Deferred<Value, unknown>
 }

 type GeneratorState = {
@@ -264,7 +268,7 @@ export class Interpreter<R> {
    readonly pending: Pending<R>
    readonly builtins: Builtins
    readonly logs?: Array<string>
-    readonly globals?: (ctx: Interpreter<R>) => ReadonlyArray<readonly [string, unknown]>
+    readonly globals?: (ctx: Interpreter<R>) => ReadonlyArray<readonly [string, Value]>
  }) {
    this.tools = options.tools
    this.pending = options.pending
@@ -278,27 +282,27 @@ export class Interpreter<R> {
    }
  }

-  run(program: Program): Effect.Effect<unknown, unknown, R> {
+  run(program: Program): Effect.Effect<Value, unknown, R> {
    return this.root.run(program)
  }

-  call(callable: unknown, thisValue: unknown, args: Array<unknown>): Effect.Effect<unknown, unknown, R> {
+  call(callable: Value, thisValue: Value, args: Array<Value>): Effect.Effect<Value, unknown, R> {
    return this.root.call(callable, thisValue, args)
  }

-  await(promise: PromiseObj): Effect.Effect<unknown, unknown, never> {
+  await(promise: PromiseObj): Effect.Effect<Value, unknown, never> {
    return this.root.await(promise)
  }

-  iterate(value: unknown) {
+  iterate(value: Value) {
    return this.root.iterate(value)
  }

  /** Runs one host tool: arguments cross as JSON and the result comes back as program values. */
  tool(
    run: (args: Array<Json | undefined>) => Effect.Effect<Json | undefined, unknown, R>,
-    args: Array<unknown>,
-  ): Effect.Effect<unknown, unknown, R> {
+    args: Array<Value>,
+  ): Effect.Effect<Value, unknown, R> {
    const ctx = this
    return Effect.gen(function* () {
      const json = yield* Effect.forEach(args, (arg) => toBoundary(ctx, arg))
@@ -321,7 +325,7 @@ class Frame<R> {
    private depth = 0,
  ) {}

-  run(program: Program): Effect.Effect<unknown, unknown, R> {
+  run(program: Program): Effect.Effect<Value, unknown, R> {
    const self = this
    // Keep top-level declarations separate so they can shadow builtins.
    this.scopes.push()
@@ -329,7 +333,7 @@ class Frame<R> {
      self.predeclareLexical(program.body)
      self.hoistFunctions(program.body)
      self.hoistVars(program.body)
-      let value: unknown = undefined
+      let value: Value = undefined
      for (const [index, statement] of program.body.entries()) {
        if (index === program.body.length - 1 && statement.type === "ExpressionStatement") {
          value = yield* self.evaluateExpression(statement.expression)
@@ -354,15 +358,12 @@ class Frame<R> {
  }

  // Fork at the call site so admission and hooks occur when the call is made.
-  private createToolCallPromise(
-    path: ReadonlyArray<string>,
-    args: Array<unknown>,
-  ): Effect.Effect<PromiseObj, never, R> {
+  private createToolCallPromise(path: ReadonlyArray<string>, args: Array<Value>): Effect.Effect<PromiseObj, never, R> {
    return this.ctx.pending.create(this.ctx.tool((json) => this.ctx.tools.execute(path, json), args))
  }

  // Fiber exits make settlement idempotent; yielding prevents inline continuation.
-  await(promise: PromiseObj): Effect.Effect<unknown, unknown, never> {
+  await(promise: PromiseObj): Effect.Effect<Value, unknown, never> {
    const pending = this.ctx.pending
    return Effect.suspend(() => {
      pending.markObserved(promise)
@@ -453,7 +454,7 @@ class Frame<R> {
  }

  // NamedEvaluation: an anonymous function definition takes the name of what it is assigned to.
-  private evaluateNamed(node: Expression, name: string): Effect.Effect<unknown, unknown, R> {
+  private evaluateNamed(node: Expression, name: string): Effect.Effect<Value, unknown, R> {
    if (node.type === "ArrowFunctionExpression" || (node.type === "FunctionExpression" && !node.id)) {
      return Effect.sync(() => this.createFunction(node, name))
    }
@@ -655,7 +656,7 @@ class Frame<R> {
      const iterator = cursor === undefined ? yield* self.customIterator(right, node, awaiting) : undefined
      if (iterator === undefined && cursor === undefined) {
        throw invalidData(
-          `${awaiting ? "for await...of" : "for...of"} requires an array, string, Map, Set, URLSearchParams, or Headers, or custom iterator value.`,
+          `${awaiting ? "for await...of" : "for...of"} requires an iterable value, received ${describeValue(right)}.`,
          node,
        )
      }
@@ -671,7 +672,7 @@ class Frame<R> {
      }
      const assignment = left.type === "VariableDeclaration" ? undefined : left

-      const evaluateBody = (value: unknown) =>
+      const evaluateBody = (value: Value) =>
        Effect.gen(function* () {
          if (declared?.lexical) {
            self.scopes.push()
@@ -720,7 +721,7 @@ class Frame<R> {
    )
  }

-  private awaitValue(value: unknown): Effect.Effect<unknown, unknown, R> {
+  private awaitValue(value: Value): Effect.Effect<Value, unknown, R> {
    return Effect.flatMap(resolvePromise(this.ctx, value), (promise) =>
      Effect.ensuring(
        this.await(promise),
@@ -731,10 +732,10 @@ class Frame<R> {

  private awaitAsyncFromSyncValue(
    iterator: CustomIterator,
-    value: unknown,
+    value: Value,
    node: AstNode | undefined,
    closeOnRejection: boolean,
-  ): Effect.Effect<unknown, unknown, R> {
+  ): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.gen(function* () {
      const settled = yield* Effect.exit(self.awaitValue(value))
@@ -746,7 +747,7 @@ class Frame<R> {
    })
  }

-  iterate(value: unknown, node?: AstNode) {
+  iterate(value: Value, node?: AstNode) {
    const cursor = this.hostCursor(value)
    if (cursor !== undefined) return Effect.succeed(cursor)
    const self = this
@@ -760,40 +761,24 @@ class Frame<R> {
    )
  }

-  private hostCursor(value: unknown) {
+  private hostCursor(value: Value) {
    const iterator =
-      value instanceof Arr
-        ? value.items[Symbol.iterator]()
-        : typeof value === "string"
-          ? value[Symbol.iterator]()
-          : value instanceof MapObj
-            ? value.map.entries()
-            : value instanceof SetObj
-              ? value.set.values()
-              : value instanceof URLSearchParamsObj
-                ? value.params.entries()
-                : value instanceof HeadersObj
-                  ? value.headers.entries()
-                  : value instanceof Bytes
-                    ? value.bytes.values()
-                    : value instanceof IteratorObj
-                      ? value.iterator
-                      : undefined
+      typeof value === "string"
+        ? value[Symbol.iterator]()
+        : value instanceof Obj
+          ? value.iterator(this.ctx.builtins)
+          : undefined
    if (iterator === undefined) return undefined
-    const proto = this.ctx.builtins.Array
    return {
      next: Effect.sync(() => {
        const step = iterator.next()
-        return {
-          done: Boolean(step.done),
-          value: Array.isArray(step.value) ? new Arr(proto, step.value) : step.value,
-        }
+        return { done: Boolean(step.done), value: step.value }
      }),
      close: Effect.void,
    }
  }

-  private customIterator(value: unknown, node: AstNode | undefined, allowAsync = true) {
+  private customIterator(value: Value, node: AstNode | undefined, allowAsync = true) {
    if (!(value instanceof Obj)) return Effect.undefined
    const asyncMethod = allowAsync ? get(value, AsyncIteratorSymbol) : undefined
    const method = asyncMethod ?? get(value, IteratorSymbol)
@@ -883,18 +868,18 @@ class Frame<R> {
    })
  }

-  private requireIteratorObject(value: unknown, context: string, node?: AstNode): Obj {
+  private requireIteratorObject(value: Value, context: string, node?: AstNode): Obj {
    if (value instanceof Obj) return value
    throw typeError(`${context} must be an object.`, node)
  }

-  private requireIteratorMethod(value: unknown, context: string, node?: AstNode): unknown {
+  private requireIteratorMethod(value: Value, context: string, node?: AstNode): Value {
    if (typeofValue(value) === "function") return value
    throw typeError(`${context} must be a function.`, node)
  }

  // for...in over null/undefined iterates nothing, like JS.
-  private enumerableKeys(value: unknown, node: AstNode): Array<string> {
+  private enumerableKeys(value: Value, node: AstNode): Array<string> {
    if (value instanceof ToolReference) return [...this.ctx.tools.keys(value.path)]
    if (value === null || value === undefined) return []
    return keys(enumerableSource(this.ctx, "for...in", value, node))
@@ -1058,7 +1043,7 @@ class Frame<R> {

  private declarePattern(
    pattern: Pattern,
-    value: unknown,
+    value: Value,
    mutable: boolean,
    node: AstNode,
    initialize = false,
@@ -1118,7 +1103,7 @@ class Frame<R> {
    })
  }

-  private assignPattern(pattern: Pattern, value: unknown, node: AstNode): Effect.Effect<void, unknown, R> {
+  private assignPattern(pattern: Pattern, value: Value, node: AstNode): Effect.Effect<void, unknown, R> {
    const self = this
    return Effect.gen(function* () {
      if (pattern.type === "Identifier") {
@@ -1170,7 +1155,7 @@ class Frame<R> {
    })
  }

-  private evaluateDefault(pattern: AssignmentPattern): Effect.Effect<unknown, unknown, R> {
+  private evaluateDefault(pattern: AssignmentPattern): Effect.Effect<Value, unknown, R> {
    return pattern.left.type === "Identifier"
      ? this.evaluateNamed(pattern.right, pattern.left.name)
      : this.evaluateExpression(pattern.right)
@@ -1178,8 +1163,8 @@ class Frame<R> {

  private destructureArrayPattern(
    pattern: ArrayPattern,
-    value: unknown,
-    consume: (target: Pattern, value: unknown, context: AstNode) => Effect.Effect<void, unknown, R>,
+    value: Value,
+    consume: (target: Pattern, value: Value, context: AstNode) => Effect.Effect<void, unknown, R>,
  ): Effect.Effect<void, unknown, R> {
    const self = this
    return Effect.gen(function* () {
@@ -1203,7 +1188,7 @@ class Frame<R> {
        done = step.done
        if (element === null) continue
        if (element.type === "RestElement") {
-          const rest: Array<unknown> = []
+          const rest: Array<Value> = []
          if (!step.done) rest.push(step.value)
          while (!done) {
            const next = yield* cursor.next
@@ -1233,13 +1218,12 @@ class Frame<R> {
    throw unsupportedSyntax(keyNode.type, keyNode)
  }

-  private evaluateExpression(node: Expression): Effect.Effect<unknown, unknown, R> {
+  private evaluateExpression(node: Expression): Effect.Effect<Value, unknown, R> {
    switch (node.type) {
      case "Literal": {
        const regex = node.regex
        if (regex) return Effect.sync(() => constructRegExp(this.ctx.builtins, [regex.pattern, regex.flags]))
-        if (typeof node.value === "bigint") throw typeError("BigInt literals are not supported.", node)
-        return Effect.succeed(node.value)
+        return Effect.succeed(literal(node))
      }
      case "Identifier":
        return Effect.sync(() => this.scopes.get(node.name, node))
@@ -1254,7 +1238,7 @@ class Frame<R> {
      case "SequenceExpression": {
        const self = this
        return Effect.gen(function* () {
-          let result: unknown
+          let result: Value
          for (const expression of node.expressions) {
            result = yield* self.evaluateExpression(expression)
          }
@@ -1295,7 +1279,7 @@ class Frame<R> {
    }
  }

-  private evaluateNewExpression(node: NewExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateNewExpression(node: NewExpression): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.gen(function* () {
      const callee = yield* self.evaluateExpression(node.callee)
@@ -1319,7 +1303,7 @@ class Frame<R> {
    })
  }

-  private evaluateBinaryExpression(node: BinaryExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateBinaryExpression(node: BinaryExpression): Effect.Effect<Value, unknown, R> {
    const operator = node.operator
    const left = node.left
    if (left.type === "PrivateIdentifier") throw unsupportedSyntax(left.type, left)
@@ -1332,7 +1316,7 @@ class Frame<R> {
    })
  }

-  private applyBinaryOperator(operator: string, lhs: unknown, rhs: unknown, node: AstNode): unknown {
+  private applyBinaryOperator(operator: string, lhs: Value, rhs: Value, node: AstNode): Value {
    if (operator === "===") return lhs === rhs
    if (operator === "!==") return lhs !== rhs
    if (operator === "in" && rhs instanceof Obj && !containsOpaqueReference(lhs)) {
@@ -1341,14 +1325,9 @@ class Frame<R> {
    if (containsOpaqueReference(lhs) || containsOpaqueReference(rhs)) {
      throw invalidData("Binary operators require data values.", node)
    }
-    // Null-prototype data needs explicit primitive coercion; identity and `in` retain raw objects.
-    // Dates use their default string hint for addition and loose equality, and epoch time elsewhere.
-    const coerceOperand = (operand: unknown): unknown => {
-      if (operand instanceof DateObj) {
-        return operator === "+" || operator === "==" || operator === "!=" ? coerceToString(operand) : operand.time
-      }
-      return operand !== null && typeof operand === "object" ? coerceToString(operand) : operand
-    }
+    // Addition and loose equality use the default hint; every other operator asks for a number.
+    const hint = operator === "+" || operator === "==" || operator === "!=" ? "default" : "number"
+    const coerceOperand = (operand: Value) => (operand instanceof Obj ? operand.toPrimitive(hint) : operand)
    const bothObjects = lhs !== null && typeof lhs === "object" && rhs !== null && typeof rhs === "object"
    const l = coerceOperand(lhs)
    const r = coerceOperand(rhs)
@@ -1402,7 +1381,7 @@ class Frame<R> {
    }
  }

-  private evaluateLogicalExpression(node: LogicalExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateLogicalExpression(node: LogicalExpression): Effect.Effect<Value, unknown, R> {
    const operator = node.operator
    return Effect.flatMap(this.evaluateExpression(node.left), (left) => {
      if (operator === "&&") return left ? this.evaluateExpression(node.right) : Effect.succeed(left)
@@ -1413,7 +1392,7 @@ class Frame<R> {
    })
  }

-  private evaluateUnaryExpression(node: UnaryExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateUnaryExpression(node: UnaryExpression): Effect.Effect<Value, unknown, R> {
    const operator = node.operator
    const argument = node.argument
    if (operator === "delete") return this.evaluateDeleteExpression(argument)
@@ -1428,13 +1407,8 @@ class Frame<R> {
      if (containsOpaqueReference(value)) {
        throw invalidData("Unary operators require data values.", node)
      }
-      const operand =
-        value instanceof DateObj
-          ? value.time
-          : value !== null && typeof value === "object"
-            ? coerceToString(value)
-            : value
-      let result: unknown
+      const operand = value instanceof Obj ? value.toPrimitive("number") : value
+      let result: Value
      switch (operator) {
        case "+":
          result = +(operand as number)
@@ -1452,7 +1426,7 @@ class Frame<R> {
    })
  }

-  private evaluateAssignmentExpression(node: AssignmentExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateAssignmentExpression(node: AssignmentExpression): Effect.Effect<Value, unknown, R> {
    const left = node.left
    const operator = node.operator
    const self = this
@@ -1492,9 +1466,9 @@ class Frame<R> {
    node: AssignmentExpression,
    left: Pattern,
    operator: string,
-  ): Effect.Effect<unknown, unknown, R> {
+  ): Effect.Effect<Value, unknown, R> {
    const self = this
-    const shouldAssign = (current: unknown): boolean =>
+    const shouldAssign = (current: Value): boolean =>
      operator === "??=" ? current === null || current === undefined : operator === "||=" ? !current : Boolean(current)
    if (left.type === "Identifier") {
      const name = left.name
@@ -1519,7 +1493,7 @@ class Frame<R> {
    throw typeError("Assignment target must be an Identifier or MemberExpression.", left)
  }

-  private evaluateUpdateExpression(node: UpdateExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateUpdateExpression(node: UpdateExpression): Effect.Effect<Value, unknown, R> {
    const operator = node.operator
    const argument = node.argument
    const prefix = node.prefix
@@ -1532,7 +1506,7 @@ class Frame<R> {

    // CodeMode numeric coercion, not host Number(): null-prototype data objects would make
    // the host throw during ToPrimitive, and opaque runtime references must reject clearly.
-    const operand = (current: unknown): number => {
+    const operand = (current: Value): number => {
      if (containsOpaqueReference(current)) {
        throw invalidData(`'${operator}' requires a data value.`, argument)
      }
@@ -1561,7 +1535,7 @@ class Frame<R> {
  }

  // EvaluateCall: a member callee supplies its base object as `this`; anything else calls with undefined.
-  private evaluateCallExpression(node: CallExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateCallExpression(node: CallExpression): Effect.Effect<Value, unknown, R> {
    const callee = node.callee

    const self = this
@@ -1579,7 +1553,7 @@ class Frame<R> {
    })
  }

-  private readMethod(node: MemberExpression): Effect.Effect<{ callable: unknown; thisValue: unknown }, unknown, R> {
+  private readMethod(node: MemberExpression): Effect.Effect<{ callable: Value; thisValue: Value }, unknown, R> {
    return Effect.map(this.getMemberReference(node), (reference) => {
      if (reference === OptionalShortCircuit) return { callable: OptionalShortCircuit, thisValue: undefined }
      if (reference instanceof ToolReference) return { callable: reference, thisValue: undefined }
@@ -1590,12 +1564,12 @@ class Frame<R> {

  // The single dispatch for every invocation: call expressions and callbacks share it.
  call(
-    callable: unknown,
-    thisValue: unknown,
-    args: Array<unknown>,
+    callable: Value,
+    thisValue: Value,
+    args: Array<Value>,
    node?: AstNode,
    callee?: Expression,
-  ): Effect.Effect<unknown, unknown, R> {
+  ): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.gen(function* () {
      if (callable instanceof ToolReference) {
@@ -1613,7 +1587,7 @@ class Frame<R> {
  }

  // Built-ins throw without a location, synchronously or inside their Effect; the call site supplies it.
-  private native(body: () => Effect.Effect<unknown, unknown, R>, node?: AstNode): Effect.Effect<unknown, unknown, R> {
+  private native(body: () => Effect.Effect<Value, unknown, R>, node?: AstNode): Effect.Effect<Value, unknown, R> {
    return Effect.provideService(
      Effect.catchDefect(Effect.suspend(body), (defect) => Effect.die(locate(defect, node))),
      CallSite,
@@ -1623,10 +1597,10 @@ class Frame<R> {

  private evaluateCallArguments(
    argNodes: ReadonlyArray<Expression | SpreadElement>,
-  ): Effect.Effect<Array<unknown>, unknown, R> {
+  ): Effect.Effect<Array<Value>, unknown, R> {
    const self = this
    return Effect.gen(function* () {
-      const args: Array<unknown> = []
+      const args: Array<Value> = []
      for (const argNode of argNodes) {
        if (argNode.type === "SpreadElement") {
          const spread = yield* self.evaluateExpression(argNode.argument)
@@ -1646,7 +1620,7 @@ class Frame<R> {
  }

  // A callback invoked by a built-in runs below the call that invoked the built-in, so the deeper of the two counts.
-  invokeFunction(fn: Fn, args: Array<unknown>, node?: AstNode): Effect.Effect<unknown, unknown, R> {
+  invokeFunction(fn: Fn, args: Array<Value>, node?: AstNode): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.flatMap(CallSite, (site) => {
      const depth = Math.max(self.depth, site.depth) + 1
@@ -1693,16 +1667,16 @@ class Frame<R> {

  private createGenerator(
    invocation: Frame<R>,
-    run: Effect.Effect<unknown, unknown, R>,
+    run: Effect.Effect<Value, unknown, R>,
    asynchronous: boolean,
  ): GeneratorObj {
    const state: GeneratorState = { started: false, completed: false, draining: false, pending: [], pendingIndex: 0 }
    invocation.generatorState = state
    invocation.generatorAsync = asynchronous
    const builtins = this.ctx.builtins
-    const result = (value: unknown, done: boolean) => record(builtins.Object, { value, done })
-    const request = (kind: GeneratorRequestKind, value: unknown) => {
-      const request = { kind, value, response: Deferred.makeUnsafe<unknown, unknown>() }
+    const result = (value: Value, done: boolean) => record(builtins.Object, { value, done })
+    const request = (kind: GeneratorRequestKind, value: Value) => {
+      const request = { kind, value, response: Deferred.makeUnsafe<Value, unknown>() }
      if (!asynchronous && state.active) return Effect.die(typeError("Generator is already running."))
      if (asynchronous && (state.completed || (!state.started && kind !== "next"))) {
        state.started = true
@@ -1773,7 +1747,7 @@ class Frame<R> {

  private completeGeneratorRequests(state: GeneratorState, asynchronous: boolean): Effect.Effect<void, never, R> {
    const self = this
-    const result = (value: unknown, done: boolean) => record(self.ctx.builtins.Object, { value, done })
+    const result = (value: Value, done: boolean) => record(self.ctx.builtins.Object, { value, done })
    return Effect.gen(function* () {
      while (true) {
        const pending = self.dequeueGeneratorRequest(state)
@@ -1819,7 +1793,7 @@ class Frame<R> {
    return request
  }

-  private evaluateYieldExpression(node: YieldExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateYieldExpression(node: YieldExpression): Effect.Effect<Value, unknown, R> {
    const argument = node.argument
    const self = this
    return Effect.gen(function* () {
@@ -1834,7 +1808,7 @@ class Frame<R> {
    })
  }

-  private suspendGenerator(value: unknown, node: AstNode): Effect.Effect<unknown, unknown, R> {
+  private suspendGenerator(value: Value, node: AstNode): Effect.Effect<Value, unknown, R> {
    const state = this.generatorState
    if (!state?.active) throw typeError("Generator has no active request.", node)
    Deferred.doneUnsafe(state.active.response, Exit.succeed(record(this.ctx.builtins.Object, { value, done: false })))
@@ -1849,20 +1823,11 @@ class Frame<R> {
    })
  }

-  private delegateYield(value: unknown, node: AstNode): Effect.Effect<unknown, unknown, R> {
+  private delegateYield(value: Value, node: AstNode): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.gen(function* () {
-      if (
-        value instanceof Arr ||
-        typeof value === "string" ||
-        value instanceof MapObj ||
-        value instanceof SetObj ||
-        value instanceof URLSearchParamsObj ||
-        value instanceof HeadersObj ||
-        value instanceof Bytes
-      ) {
-        const cursor = yield* self.iterate(value, node)
-        if (!cursor) throw typeError("Built-in iterator is unavailable.", node)
+      const cursor = self.hostCursor(value)
+      if (cursor !== undefined) {
        while (true) {
          const step = yield* cursor.next
          if (step.done) return undefined
@@ -1886,7 +1851,7 @@ class Frame<R> {
      const iterator = yield* self.customIterator(value, node, self.generatorAsync)
      if (!iterator) throw typeError("yield* requires a compatible iterable value.", node)
      let kind: GeneratorRequestKind = "next"
-      let input: unknown = undefined
+      let input: Value = undefined
      while (true) {
        const method = kind === "next" ? iterator.next : get(iterator.iterator, kind)
        if (method === undefined || method === null) {
@@ -1906,7 +1871,7 @@ class Frame<R> {
          node,
        )
        const done = Boolean(get(result, "done"))
-        const resultValue: unknown =
+        const resultValue: Value =
          self.generatorAsync && !iterator.asynchronous
            ? yield* self.awaitAsyncFromSyncValue(iterator, get(result, "value"), node, kind !== "return" && !done)
            : get(result, "value")
@@ -1915,7 +1880,7 @@ class Frame<R> {
          return resultValue
        }

-        const resumed: Exit.Exit<unknown, unknown> = yield* Effect.exit(self.suspendGenerator(resultValue, node))
+        const resumed: Exit.Exit<Value, unknown> = yield* Effect.exit(self.suspendGenerator(resultValue, node))
        if (Exit.isSuccess(resumed)) {
          kind = "next"
          input = resumed.value
@@ -1956,7 +1921,7 @@ class Frame<R> {
        } else if (keyNode.type === "Identifier") {
          key = keyNode.name
        } else if (keyNode.type === "Literal") {
-          key = self.toPropertyKey(keyNode.value, keyNode)
+          key = self.toPropertyKey(literal(keyNode), keyNode)
        } else {
          throw typeError("Unsupported object property key shape.", keyNode)
        }
@@ -1975,7 +1940,7 @@ class Frame<R> {
  }

  private evaluateArrayExpression(node: ArrayExpression): Effect.Effect<Arr, unknown, R> {
-    const values: Array<unknown> = []
+    const values: Array<Value> = []

    const self = this
    return Effect.gen(function* () {
@@ -2030,13 +1995,13 @@ class Frame<R> {
    })
  }

-  private evaluateConditionalExpression(node: ConditionalExpression): Effect.Effect<unknown, unknown, R> {
+  private evaluateConditionalExpression(node: ConditionalExpression): Effect.Effect<Value, unknown, R> {
    return Effect.flatMap(this.evaluateExpression(node.test), (test) =>
      this.evaluateExpression(test ? node.consequent : node.alternate),
    )
  }

-  private applyCompoundAssignment(operator: string, current: unknown, incoming: unknown, node: AstNode): unknown {
+  private applyCompoundAssignment(operator: string, current: Value, incoming: Value, node: AstNode): Value {
    if (!compoundOperators.has(operator)) {
      throw typeError(`Unsupported assignment operator '${operator}'.`, node)
    }
@@ -2045,7 +2010,7 @@ class Frame<R> {

  private getMemberReference(
    node: MemberExpression,
-  ): Effect.Effect<MemberReference | ToolReference | { value: unknown } | typeof OptionalShortCircuit, unknown, R> {
+  ): Effect.Effect<MemberReference | ToolReference | { value: Value } | typeof OptionalShortCircuit, unknown, R> {
    const objectNode = node.object
    const propertyNode = node.property
    if (objectNode.type === "Super") throw unsupportedSyntax(objectNode.type, objectNode)
@@ -2071,16 +2036,14 @@ class Frame<R> {

      if (objectValue instanceof Obj) return { target: objectValue, key, receiver: objectValue }

-      // Primitives read through their wrapper prototype without being boxed; strings own length and indexes.
-      const builtins = self.ctx.builtins
+      // Strings own length and indexes; every other primitive property reads through the wrapper prototype.
      if (typeof objectValue === "string") {
        if (key === "length") return { value: objectValue.length }
        const index = typeof key === "symbol" ? undefined : parseArrayIndex(key)
        if (index !== undefined) return { value: objectValue[index] }
-        return { target: builtins.String, key, receiver: objectValue }
      }
-      if (typeof objectValue === "number") return { target: builtins.Number, key, receiver: objectValue }
-      if (typeof objectValue === "boolean") return { target: builtins.Boolean, key, receiver: objectValue }
+      const proto = primitivePrototype(self.ctx.builtins, objectValue)
+      if (proto !== undefined) return { target: proto, key, receiver: objectValue }

      if (objectValue === null || objectValue === undefined) {
        throw typeError(`Cannot read properties of ${objectValue} (reading '${String(key)}').`, objectNode)
@@ -2089,7 +2052,7 @@ class Frame<R> {
    })
  }

-  private readReference(reference: MemberReference, node: MemberExpression): unknown {
+  private readReference(reference: MemberReference, node: MemberExpression): Value {
    // Reject unknown promise properties so a missing await cannot hide.
    if (reference.target instanceof PromiseObj && !has(reference.target, reference.key)) {
      throw invalidData(
@@ -2101,7 +2064,7 @@ class Frame<R> {
  }

  // Accessors throw without a location; the member or pattern that read them supplies it.
-  private readProperty(target: Obj, key: PropertyKey, node: AstNode, receiver: unknown = target): unknown {
+  private readProperty(target: Obj, key: PropertyKey, node: AstNode, receiver: Value = target): Value {
    try {
      return get(target, key, receiver)
    } catch (error) {
@@ -2109,7 +2072,7 @@ class Frame<R> {
    }
  }

-  private readMember(node: MemberExpression): Effect.Effect<unknown, unknown, R> {
+  private readMember(node: MemberExpression): Effect.Effect<Value, unknown, R> {
    return Effect.map(this.getMemberReference(node), (reference) => {
      if (reference === OptionalShortCircuit) return OptionalShortCircuit
      if (reference instanceof ToolReference) return reference
@@ -2118,7 +2081,7 @@ class Frame<R> {
    })
  }

-  private writeMember(node: MemberExpression, value: unknown): Effect.Effect<unknown, unknown, R> {
+  private writeMember(node: MemberExpression, value: Value): Effect.Effect<Value, unknown, R> {
    return this.modifyMember(node, () => Effect.succeed({ write: true, next: value, result: value }))
  }

@@ -2140,8 +2103,8 @@ class Frame<R> {
  // Resolve side-effecting object and key expressions exactly once.
  private modifyMember(
    node: MemberExpression,
-    compute: (current: unknown) => Effect.Effect<{ write: boolean; next: unknown; result: unknown }, unknown, R>,
-  ): Effect.Effect<unknown, unknown, R> {
+    compute: (current: Value) => Effect.Effect<{ write: boolean; next: Value; result: Value }, unknown, R>,
+  ): Effect.Effect<Value, unknown, R> {
    const self = this
    return Effect.gen(function* () {
      const reference = yield* self.getMemberReference(node)
@@ -2161,7 +2124,7 @@ class Frame<R> {
    })
  }

-  private assignToReference(target: Obj, key: PropertyKey, next: unknown, node: AstNode): void {
+  private assignToReference(target: Obj, key: PropertyKey, next: Value, node: AstNode): void {
    const written = (() => {
      try {
        rejectCircularInsertion(
@@ -2179,7 +2142,7 @@ class Frame<R> {
    throw typeError(`Cannot assign to read only property '${String(key)}'.`, node)
  }

-  private toPropertyKey(value: unknown, node: AstNode): PropertyKey {
+  private toPropertyKey(value: Value, node: AstNode): PropertyKey {
    if (typeof value === "string" || typeof value === "number") {
      return value
    }
@@ -1,5 +1,5 @@
 import { Effect } from "effect"
-import { define, hidden, Native, Arr, ErrorObj, Obj } from "./objects.js"
+import { define, hidden, Native, Arr, ErrorObj, Obj, type Value } from "./objects.js"

 export const errorTypes = [
  "Error",
@@ -52,6 +52,14 @@ export const createErrorValue = (prototype: Obj, message: string | undefined): E
  return value
 }

+/** The prototype a primitive reads its methods from without being boxed; none for null, undefined, and symbols. */
+export const primitivePrototype = (builtins: Builtins, value: Value): Obj | undefined => {
+  if (typeof value === "string") return builtins.String
+  if (typeof value === "number") return builtins.Number
+  if (typeof value === "boolean") return builtins.Boolean
+  return undefined
+}
+
 export const createBuiltins = (): Builtins => {
  const object = new Obj(null)
  // Function.prototype is itself callable and returns undefined.
@@ -2,7 +2,7 @@ import type { Node } from "acorn"
 import { Context } from "effect"
 import type { ErrorType } from "./intrinsics.js"
 import type { DiagnosticKind } from "../codemode.js"
-import type { ErrorObj } from "./objects.js"
+import type { ErrorObj, Value } from "./objects.js"

 /** Any parsed node; the interpreter narrows on `type` and reads `loc` for diagnostics. */
 export type AstNode = Node
@@ -14,13 +14,13 @@ export const CallSite = Context.Reference<{ readonly node?: AstNode; readonly de

 export type Binding = {
  mutable: boolean
-  value: unknown
+  value: Value
  initialized?: boolean
 }

 export type StatementResult =
  | { kind: "none" }
-  | { kind: "return"; value: unknown }
+  | { kind: "return"; value: Value }
  | { kind: "break"; label?: string }
  | { kind: "continue"; label?: string }

@@ -31,11 +31,11 @@ export const IteratorSymbol: unique symbol = Symbol("codemode.iterator")
 export const IteratorSymbols = [AsyncIteratorSymbol, IteratorSymbol] as const

 export class Throw {
-  constructor(readonly value: unknown) {}
+  constructor(readonly value: Value) {}
 }

 export class GeneratorReturn {
-  constructor(readonly value: unknown) {}
+  constructor(readonly value: Value) {}
 }

 export const OptionalShortCircuit: unique symbol = Symbol("codemode.optional-short-circuit")
@@ -83,9 +83,6 @@ export const unsupportedSyntax = (kind: string, node: AstNode): PendingThrow =>
    [supportedSyntaxMessage],
  )

-export const isRecord = (value: unknown): value is Record<string, unknown> =>
-  typeof value === "object" && value !== null
-
 export const sourceLocation = (node: AstNode): { readonly line: number; readonly column: number } => ({
  line: Math.max(1, (node.loc?.start.line ?? 2) - 1),
  column: Math.max(1, (node.loc?.start.column ?? 4) - 3),
@@ -1,18 +1,18 @@
 import { Effect } from "effect"
 import type { Builtins } from "./intrinsics.js"
 import { typeError } from "./model.js"
-import { type Callable, define, frozen, hidden, Native, type NativeOptions, Obj } from "./objects.js"
+import { type Callable, define, frozen, hidden, Native, type NativeOptions, Obj, type Value } from "./objects.js"
 import { describeValue } from "./references.js"

-/** A native function body: a plain value, a thrown `PendingThrow`, or an Effect. */
-export type Impl = (thisValue: unknown, args: Array<unknown>) => unknown
+/** A native function body: a value, a thrown `PendingThrow`, or an Effect of a value. */
+export type Impl = (thisValue: Value, args: Array<Value>) => Value | Effect.Effect<Value, unknown, unknown>

 // The dispatch in `Frame.call` suspends every native call, so a synchronous throw here is a defect.
 const lift =
  <R>(impl: Impl) =>
-  (thisValue: unknown, args: Array<unknown>): Effect.Effect<unknown, unknown, R> => {
+  (thisValue: Value, args: Array<Value>): Effect.Effect<Value, unknown, R> => {
    const result = impl(thisValue, args)
-    return Effect.isEffect(result) ? (result as Effect.Effect<unknown, unknown, R>) : Effect.succeed(result)
+    return Effect.isEffect(result) ? (result as Effect.Effect<Value, unknown, R>) : Effect.succeed(result)
  }

 export const native = <R>(builtins: Builtins, options: NativeOptions<R>): Native<R> =>
@@ -27,7 +27,7 @@ export const methods = (builtins: Builtins, target: Obj, table: ReadonlyArray<Me
  for (const [name, length, impl] of table) define(target, name, fn(builtins, name, length, impl), hidden)
 }

-export const constants = (target: Obj, table: Record<string, unknown>): void => {
+export const constants = (target: Obj, table: Record<string, Value>): void => {
  for (const [name, value] of Object.entries(table)) define(target, name, value, frozen)
 }

@@ -54,7 +54,7 @@ export const prototypeFrom = (newTarget: Callable, fallback: Obj): Obj => {
 /** Narrows a method receiver to the built-in it belongs to, or throws the TypeError JS would. */
 export const receiver = <T extends Obj>(
  cls: abstract new (...args: never) => T,
-  thisValue: unknown,
+  thisValue: Value,
  method: string,
 ): T => {
  if (thisValue instanceof cls) return thisValue
@@ -1,5 +1,7 @@
 import type { BlockStatement, Expression, Pattern } from "acorn"
 import type { Effect, Fiber } from "effect"
+import { ToolReference } from "../tool-runtime.js"
+import type { Builtins } from "./intrinsics.js"
 import { checkArrayLength } from "./limits.js"
 import {
  AsyncIteratorSymbol,
@@ -16,12 +18,12 @@ export type Attributes = {
  readonly configurable: boolean
 }

-export type Getter = (receiver: unknown) => unknown
-export type Setter = (receiver: unknown, value: unknown) => void
+export type Getter = (receiver: Value) => Value
+export type Setter = (receiver: Value, value: Value) => void

 /** One own property: a data slot or a native accessor pair. */
 export type Slot =
-  | { value: unknown; writable: boolean; enumerable: boolean; configurable: boolean }
+  | { value: Value; writable: boolean; enumerable: boolean; configurable: boolean }
  | { get: Getter | undefined; set: Setter | undefined; enumerable: boolean; configurable: boolean }

 /** Ordinary assignment: writable, enumerable, configurable. */
@@ -33,33 +35,119 @@ export const readonly: Attributes = { writable: false, enumerable: false, config
 /** Constants such as `Math.PI` and a constructor's `prototype`. */
 export const frozen: Attributes = { writable: false, enumerable: false, configurable: false }

-/** An object owned by the program: own properties plus a prototype link. */
+/**
+ * An object owned by the program: own properties plus a prototype link. Subclasses answer, in one place, how a
+ * built-in kind of object prints, coerces, iterates, and crosses to the host.
+ */
 export class Obj {
  readonly props = new Map<string | symbol, Slot>()
  constructor(public proto: Obj | null) {}
+
+  /** The class name `Object.prototype.toString` reports: `[object Map]`. */
+  readonly tag: string = "Object"
+
+  /** How diagnostics refer to a value of this kind. */
+  get describe(): string {
+    if (this.tag === "Object") return "a data object"
+    return `${/^[AEIO]/.test(this.tag) ? "an" : "a"} ${this.tag}`
+  }
+
+  /** ToString without consulting program-defined methods. */
+  toString(): string {
+    return `[object ${this.tag}]`
+  }
+
+  /** ToPrimitive without consulting program-defined methods: only a Date answers a number hint differently. */
+  toPrimitive(hint: "default" | "number" | "string"): string | number {
+    return this.toString()
+  }
+
+  /** ToNumber without consulting program-defined methods. */
+  toNumber(): number {
+    return Number(this.toPrimitive("number"))
+  }
+
+  /** How `console.log` shows the value; `item` formats a child with cycle and depth tracking. */
+  inspect(item: (value: Value) => string): string {
+    return `{${entries(this)
+      .map(([key, value]) => `${JSON.stringify(key)}:${item(value)}`)
+      .join(",")}}`
+  }
+
+  /** A copy the host can hold; `item` converts a child. A `__proto__` key never reaches host code. */
+  toHost(item: (value: Value) => unknown): unknown {
+    return Object.fromEntries(
+      entries(this)
+        .filter(([key]) => key !== "__proto__")
+        .map(([key, value]) => [key, item(value)]),
+    )
+  }
+
+  /** The built-in iteration `for...of` and spread use, when this kind of object has one. */
+  iterator(builtins: Builtins): Iterator<Value, undefined> | undefined {
+    return undefined
+  }
 }

 export class Arr extends Obj {
+  override readonly tag = "Array"
  constructor(
    proto: Obj,
-    readonly items: Array<unknown> = [],
+    readonly items: Array<Value> = [],
  ) {
    super(proto)
  }
+  override get describe() {
+    return "an array"
+  }
+  override toString() {
+    return this.items.map((item) => (item === null || item === undefined ? "" : coerceToString(item))).join(",")
+  }
+  override inspect(item: (value: Value) => string) {
+    return `[${this.items.map(item).join(",")}]`
+  }
+  override toHost(item: (value: Value) => unknown) {
+    return this.items.map(item)
+  }
+  override iterator() {
+    return this.items.values()
+  }
 }

 /** An object with the [[ErrorData]] slot: what `Error.prototype.toString` and the host boundary recognize as an error. */
 export class ErrorObj extends Obj {
+  override readonly tag = "Error"
  /** The interpreter failure this error materialized from, so rethrowing it keeps the diagnostic kind and location. */
  host?: PendingThrow
+  /** Error.prototype.toString: "name: message", or just one when the other is empty. */
+  override toString() {
+    const name = get(this, "name")
+    const message = get(this, "message")
+    const shownName = typeof name === "string" ? name : "Error"
+    const shownMessage = typeof message === "string" ? message : ""
+    if (shownMessage === "") return shownName
+    if (shownName === "") return shownMessage
+    return `${shownName}: ${shownMessage}`
+  }
 }

-export abstract class Callable extends Obj {
+/** Interpreter machinery a program can hold but never inspect, serialize, or hand to the host. */
+export abstract class Opaque extends Obj {
+  override inspect() {
+    return "[opaque reference]"
+  }
+}
+
+export abstract class Callable extends Opaque {
+  override readonly tag = "Function"
  constructor(proto: Obj, name: string, length: number) {
    super(proto)
    define(this, "length", length, readonly)
    define(this, "name", name, readonly)
  }
+  override get describe() {
+    return "a function"
+  }
 }

 export class Fn extends Callable {
@@ -77,8 +165,8 @@ export class Fn extends Callable {
  }
 }

-export type NativeCall<R> = (thisValue: unknown, args: Array<unknown>) => Effect.Effect<unknown, unknown, R>
-export type NativeConstruct<R> = (args: Array<unknown>, newTarget: Callable) => Effect.Effect<unknown, unknown, R>
+export type NativeCall<R> = (thisValue: Value, args: Array<Value>) => Effect.Effect<Value, unknown, R>
+export type NativeConstruct<R> = (args: Array<Value>, newTarget: Callable) => Effect.Effect<Value, unknown, R>

 export type NativeOptions<R> = {
  readonly name: string
@@ -103,79 +191,163 @@ export class Native<R = never> extends Callable {
  }
 }

-export class PromiseObj extends Obj {
+export class PromiseObj extends Opaque {
+  override readonly tag = "Promise"
  constructor(
    proto: Obj,
-    readonly fiber: Fiber.Fiber<unknown, unknown>,
+    readonly fiber: Fiber.Fiber<Value, unknown>,
  ) {
    super(proto)
  }
+  override get describe() {
+    return "an un-awaited Promise"
+  }
+  override inspect() {
+    return "[Promise (await it to get its value)]"
+  }
 }

-export class GeneratorObj extends Obj {
+export class GeneratorObj extends Opaque {
+  override readonly tag = "Generator"
  constructor(
    proto: Obj,
    readonly asynchronous: boolean,
-    readonly request: (kind: GeneratorRequestKind, value: unknown) => Effect.Effect<unknown, unknown, unknown>,
+    readonly request: (kind: GeneratorRequestKind, value: Value) => Effect.Effect<Value, unknown, unknown>,
  ) {
    super(proto)
  }
+  override get describe() {
+    return "a generator"
+  }
 }

 /** A built-in collection iterator: live over the host collection, yielding program values. */
-export class IteratorObj extends Obj {
+export class IteratorObj extends Opaque {
+  override readonly tag = "Iterator"
  constructor(
    proto: Obj,
-    readonly iterator: IteratorObject<unknown>,
+    readonly source: IteratorObject<Value, undefined>,
  ) {
    super(proto)
  }
+  override get describe() {
+    return "an iterator"
+  }
+  override iterator() {
+    return this.source
+  }
 }

-export class DateObj extends Obj {
+/** A built-in object around a host value: data-like, so it prints as itself and crosses to extensions as a copy. */
+export abstract class Wrapper extends Obj {
+  override inspect(item: (value: Value) => string) {
+    return this.toString()
+  }
+}
+
+export class DateObj extends Wrapper {
+  override readonly tag = "Date"
  constructor(
    proto: Obj,
    public time: number,
  ) {
    super(proto)
  }
+  override toString() {
+    return Number.isFinite(this.time) ? new Date(this.time).toISOString() : "Invalid Date"
+  }
+  override toPrimitive(hint: "default" | "number" | "string") {
+    return hint === "number" ? this.time : this.toString()
+  }
+  override toHost() {
+    return new Date(this.time)
+  }
 }

-export class RegExpObj extends Obj {
+export class RegExpObj extends Wrapper {
+  override readonly tag = "RegExp"
  readonly regex: RegExp
  constructor(proto: Obj, pattern: string, flags: string) {
    super(proto)
    this.regex = new RegExp(pattern, flags)
  }
+  override toString() {
+    return `/${this.regex.source}/${this.regex.flags}`
+  }
+  override toHost() {
+    return new RegExp(this.regex.source, this.regex.flags)
+  }
 }

-export class MapObj extends Obj {
-  readonly map = new Map<unknown, unknown>()
+export class MapObj extends Wrapper {
+  override readonly tag = "Map"
+  readonly map = new Map<Value, Value>()
+  override inspect(item: (value: Value) => string) {
+    return `Map(${this.map.size}) [${[...this.map].map(([key, value]) => `[${item(key)},${item(value)}]`).join(",")}]`
+  }
+  override toHost(item: (value: Value) => unknown) {
+    return new Map([...this.map].map(([key, value]) => [item(key), item(value)]))
+  }
+  override iterator(builtins: Builtins) {
+    return this.map.entries().map((entry) => new Arr(builtins.Array, entry))
+  }
 }

-export class SetObj extends Obj {
-  readonly set = new Set<unknown>()
+export class SetObj extends Wrapper {
+  override readonly tag = "Set"
+  readonly set = new Set<Value>()
+  override inspect(item: (value: Value) => string) {
+    return `Set(${this.set.size}) [${[...this.set].map(item).join(",")}]`
+  }
+  override toHost(item: (value: Value) => unknown) {
+    return new Set([...this.set].map(item))
+  }
+  override iterator() {
+    return this.set.values()
+  }
 }

-export class URLSearchParamsObj extends Obj {
+export class URLSearchParamsObj extends Wrapper {
+  override readonly tag = "URLSearchParams"
  constructor(
    proto: Obj,
    readonly params: URLSearchParams,
  ) {
    super(proto)
  }
+  override toString() {
+    return this.params.toString()
+  }
+  override toHost() {
+    return new URLSearchParams(this.params)
+  }
+  override iterator(builtins: Builtins) {
+    return this.params.entries().map((entry) => new Arr(builtins.Array, entry))
+  }
 }

-export class HeadersObj extends Obj {
+export class HeadersObj extends Wrapper {
+  override readonly tag = "Headers"
  constructor(
    proto: Obj,
    readonly headers: Headers,
  ) {
    super(proto)
  }
+  override inspect() {
+    return `Headers ${JSON.stringify(Object.fromEntries(this.headers))}`
+  }
+  override toHost() {
+    return new Headers(this.headers)
+  }
+  override iterator(builtins: Builtins) {
+    // Bun's Headers typings lack the iterator helpers, so the host iterator is lifted first.
+    return Iterator.from(this.headers.entries()).map((entry) => new Arr(builtins.Array, entry))
+  }
 }

-export class URLObj extends Obj {
+export class URLObj extends Wrapper {
+  override readonly tag = "URL"
  readonly searchParams: URLSearchParamsObj
  constructor(
    proto: Obj,
@@ -185,30 +357,52 @@ export class URLObj extends Obj {
    super(proto)
    this.searchParams = new URLSearchParamsObj(searchParamsProto, url.searchParams)
  }
+  override toString() {
+    return this.url.href
+  }
+  override toHost() {
+    return new URL(this.url.href)
+  }
 }

 /** A `Uint8Array`: the host array does the byte clamping and ignores out-of-range writes, as JS does. */
-export class Bytes extends Obj {
+export class Bytes extends Wrapper {
+  override readonly tag = "Uint8Array"
  constructor(
    proto: Obj,
    readonly bytes: Uint8Array,
  ) {
    super(proto)
  }
+  override toString() {
+    return this.bytes.join(",")
+  }
+  override inspect() {
+    return `Uint8Array(${this.bytes.length}) [${this.bytes.join(",")}]`
+  }
+  override toHost() {
+    return new Uint8Array(this.bytes)
+  }
+  override iterator() {
+    return this.bytes.values()
+  }
 }

-/** Built-in objects that wrap a host value; data-like, but never plain data. */
-export const isWrapper = (
-  value: unknown,
-): value is DateObj | RegExpObj | MapObj | SetObj | URLObj | URLSearchParamsObj | HeadersObj | Bytes =>
-  value instanceof DateObj ||
-  value instanceof RegExpObj ||
-  value instanceof MapObj ||
-  value instanceof SetObj ||
-  value instanceof URLObj ||
-  value instanceof URLSearchParamsObj ||
-  value instanceof HeadersObj ||
-  value instanceof Bytes
+/** Every value a program can hold. Host values never appear here; they are copied in at the boundaries. */
+export type Value = string | number | boolean | null | undefined | symbol | Obj | ToolReference
+
+/** ToString without consulting program-defined methods. */
+export const coerceToString = (value: Value): string => (value instanceof Obj ? value.toString() : String(value))
+
+/** ToNumber without consulting program-defined methods; tool references are not numbers. */
+export const coerceToNumber = (value: Value): number => {
+  if (value instanceof Obj) return value.toNumber()
+  return value instanceof ToolReference ? Number.NaN : Number(value)
+}
+
+/** Values that cannot cross the data boundary: opaque machinery and host-backed wrappers. */
+export const isRuntimeReference = (value: Value): boolean =>
+  value instanceof Opaque || value instanceof Wrapper || value instanceof ToolReference

 const MAX_ARRAY_INDEX = 4_294_967_295

@@ -226,7 +420,7 @@ type Indexed = Arr | Bytes

 const isIndexed = (target: Obj): target is Indexed => target instanceof Arr || target instanceof Bytes

-const elements = (target: Indexed): Array<unknown> | Uint8Array => (target instanceof Arr ? target.items : target.bytes)
+const elements = (target: Indexed): Array<Value> | Uint8Array => (target instanceof Arr ? target.items : target.bytes)

 const index = (target: Obj, key: string | symbol): number | undefined =>
  isIndexed(target) && typeof key === "string" ? parseArrayIndex(key) : undefined
@@ -247,18 +441,18 @@ export const own = (target: Obj, key: PropertyKey): Slot | undefined => {
  return target.props.get(name)
 }

-const read = (slot: Slot, receiver: unknown): unknown =>
+const read = (slot: Slot, receiver: Value): Value =>
  "value" in slot ? slot.value : slot.get === undefined ? undefined : slot.get(receiver)

 export const hasOwn = (target: Obj, key: PropertyKey): boolean => own(target, key) !== undefined

-export const getOwn = (target: Obj, key: PropertyKey): unknown => {
+export const getOwn = (target: Obj, key: PropertyKey): Value => {
  const slot = own(target, key)
  return slot === undefined ? undefined : read(slot, target)
 }

 /** [[Get]]: walks the prototype chain; accessors see `receiver`, which is the primitive for wrapper prototypes. */
-export const get = (target: Obj, key: PropertyKey, receiver: unknown = target): unknown => {
+export const get = (target: Obj, key: PropertyKey, receiver: Value = target): Value => {
  for (let current: Obj | null = target; current !== null; current = current.proto) {
    const slot = own(current, key)
    if (slot !== undefined) return read(slot, receiver)
@@ -273,14 +467,14 @@ export const has = (target: Obj, key: PropertyKey): boolean => {
  return false
 }

-export const hasPrototype = (value: unknown, proto: Obj): boolean => {
+export const hasPrototype = (value: Value, proto: Obj): boolean => {
  for (let current = value instanceof Obj ? value.proto : null; current !== null; current = current.proto) {
    if (current === proto) return true
  }
  return false
 }

-const writeElement = (target: Indexed, name: string | symbol, value: unknown): boolean | undefined => {
+const writeElement = (target: Indexed, name: string | symbol, value: Value): boolean | undefined => {
  const at = index(target, name)
  if (at !== undefined) {
    if (target instanceof Bytes) target.bytes[at] = typeof value === "number" ? value : Number(value)
@@ -296,7 +490,7 @@ const writeElement = (target: Indexed, name: string | symbol, value: unknown): b
 }

 /** [[Set]]: an inherited setter or read-only property decides before an own data property is created. */
-export const set = (target: Obj, key: PropertyKey, value: unknown): boolean => {
+export const set = (target: Obj, key: PropertyKey, value: Value): boolean => {
  const name = canonical(key)
  for (let current: Obj | null = target; current !== null; current = current.proto) {
    const slot = own(current, name)
@@ -324,7 +518,7 @@ export const set = (target: Obj, key: PropertyKey, value: unknown): boolean => {
 }

 /** [[DefineOwnProperty]] for a data property, ignoring the chain. */
-export const define = (target: Obj, key: PropertyKey, value: unknown, attrs: Attributes = data): void => {
+export const define = (target: Obj, key: PropertyKey, value: Value, attrs: Attributes = data): void => {
  const name = canonical(key)
  if (isIndexed(target) && writeElement(target, name, value) !== undefined) return
  target.props.set(name, { value, ...attrs })
@@ -375,9 +569,9 @@ export const keys = (target: Obj): Array<string> =>
  ownKeys(target).filter((key): key is string => typeof key === "string" && enumerable(target, key))

 /** Own enumerable string entries: `Object.entries` and serialization. */
-export const entries = (target: Obj): Array<[string, unknown]> => keys(target).map((key) => [key, getOwn(target, key)])
+export const entries = (target: Obj): Array<[string, Value]> => keys(target).map((key) => [key, getOwn(target, key)])

-export const record = (proto: Obj, fields: Record<string, unknown>): Obj => {
+export const record = (proto: Obj, fields: Record<string, Value>): Obj => {
  const target = new Obj(proto)
  for (const [key, value] of Object.entries(fields)) define(target, key, value)
  return target
@@ -2,7 +2,7 @@ import { Cause, Deferred, Effect, Exit, Fiber, Scope } from "effect"
 import type { Diagnostic } from "../codemode.js"
 import { MAX_PENDING_PROMISES } from "./limits.js"
 import { CallSite, Throw, rangeError, typeError } from "./model.js"
-import { Callable, define, get, hidden, Arr, Fn, Obj, PromiseObj, record } from "./objects.js"
+import { Callable, define, get, hidden, Arr, Fn, Obj, PromiseObj, record, type Value } from "./objects.js"
 import { constructor, fn, methods, native, receiver, requiresNew } from "./native.js"
 import { createAggregateErrorValue, locate, materialize, normalizeError } from "./errors.js"
 import { typeofValue } from "./references.js"
@@ -10,7 +10,7 @@ import { applyCollectionCallback, isSupportedCallback } from "./callback.js"
 import type { Interpreter } from "./interpreter.js"

 // A `resolve`/`reject` handed to an executor or thenable: calling it settles the capability.
-const capability = <R>(ctx: Interpreter<R>, name: string, settle: (value: unknown) => void) =>
+const capability = <R>(ctx: Interpreter<R>, name: string, settle: (value: Value) => void) =>
  fn(ctx.builtins, name, 1, (_, args) => {
    settle(args[0])
    return undefined
@@ -31,7 +31,7 @@ export class Pending<R> {

  // Resolution bodies need the promise's own identity to reject `resolve(promise)` self-resolution.
  createWithSelf(
-    body: (self: { promise?: PromiseObj }) => Effect.Effect<unknown, unknown, R>,
+    body: (self: { promise?: PromiseObj }) => Effect.Effect<Value, unknown, R>,
  ): Effect.Effect<PromiseObj, never, R> {
    const self: { promise?: PromiseObj } = {}
    return Effect.map(this.create(body(self)), (promise) => {
@@ -40,7 +40,7 @@ export class Pending<R> {
    })
  }

-  create(effect: Effect.Effect<unknown, unknown, R>): Effect.Effect<PromiseObj, never, R> {
+  create(effect: Effect.Effect<Value, unknown, R>): Effect.Effect<PromiseObj, never, R> {
    return Effect.flatMap(CallSite, (site) => {
      if (this.active.size >= MAX_PENDING_PROMISES) {
        throw rangeError(
@@ -79,7 +79,7 @@ export class Pending<R> {
    if (id !== undefined) this.failures.delete(id)
  }

-  await(promise: PromiseObj): Effect.Effect<Exit.Exit<unknown, unknown>> {
+  await(promise: PromiseObj): Effect.Effect<Exit.Exit<Value, unknown>> {
    return Fiber.await(promise.fiber)
  }

@@ -105,9 +105,9 @@ export class Pending<R> {

 export const resolvePromiseValue = <R>(
  ctx: Interpreter<R>,
-  value: unknown,
+  value: Value,
  own?: { promise?: PromiseObj },
-): Effect.Effect<unknown, unknown, R> => {
+): Effect.Effect<Value, unknown, R> => {
  if (own?.promise !== undefined && value === own.promise) {
    return Effect.die(typeError("Chaining cycle detected: a promise cannot resolve with itself."))
  }
@@ -119,7 +119,7 @@ export const resolvePromiseValue = <R>(
  return Effect.gen(function* () {
    // Promise resolution invokes a thenable's method in a later job.
    yield* Effect.yieldNow
-    const deferred = Deferred.makeUnsafe<unknown, unknown>()
+    const deferred = Deferred.makeUnsafe<Value, unknown>()
    const resolve = capability(ctx, "resolve", (result) => Deferred.doneUnsafe(deferred, Exit.succeed(result)))
    const reject = capability(ctx, "reject", (reason) => Deferred.doneUnsafe(deferred, Exit.fail(new Throw(reason))))
    const executed = yield* Effect.exit(ctx.call(then, value, [resolve, reject]))
@@ -131,7 +131,7 @@ export const resolvePromiseValue = <R>(
  })
 }

-export const resolvePromise = <R>(ctx: Interpreter<R>, value: unknown): Effect.Effect<PromiseObj, never, R> => {
+export const resolvePromise = <R>(ctx: Interpreter<R>, value: Value): Effect.Effect<PromiseObj, never, R> => {
  if (value instanceof PromiseObj) return Effect.succeed(value)
  return ctx.pending.createWithSelf((self) => resolvePromiseValue(ctx, value, self))
 }
@@ -141,8 +141,8 @@ const promiseStatics = ["all", "allSettled", "race", "any", "resolve", "reject"]
 const invokePromiseMethod = <R>(
  ctx: Interpreter<R>,
  name: (typeof promiseStatics)[number],
-  args: Array<unknown>,
-): Effect.Effect<unknown, unknown, R> => {
+  args: Array<Value>,
+): Effect.Effect<Value, unknown, R> => {
  if (name === "resolve") {
    return resolvePromise(ctx, args[0])
  }
@@ -175,7 +175,7 @@ const invokePromiseMethod = <R>(
        )
      }
      if (name === "allSettled") {
-        const outcomes: Array<unknown> = []
+        const outcomes: Array<Value> = []
        for (const item of items) {
          const exit = yield* ctx.pending.await(item)
          if (Exit.isSuccess(exit)) {
@@ -223,8 +223,8 @@ const invokePromiseMethod = <R>(
 const instanceMethod = <R>(
  ctx: Interpreter<R>,
  name: "then" | "catch" | "finally",
-  thisValue: unknown,
-  args: Array<unknown>,
+  thisValue: Value,
+  args: Array<Value>,
 ): Effect.Effect<PromiseObj, unknown, R> => {
  const method = `Promise.prototype.${name}`
  const promise = receiver(PromiseObj, thisValue, method)
@@ -237,12 +237,12 @@ const instanceMethod = <R>(
  return chainReaction(ctx, promise, onFulfilled, onRejected, method)
 }

-const constructPromise = <R>(ctx: Interpreter<R>, executor: unknown): Effect.Effect<PromiseObj, unknown, R> => {
+const constructPromise = <R>(ctx: Interpreter<R>, executor: Value): Effect.Effect<PromiseObj, unknown, R> => {
  if (!(executor instanceof Fn)) {
    throw typeError("new Promise(...) expects an executor function (e.g. new Promise((resolve, reject) => { ... })).")
  }
  return Effect.gen(function* () {
-    const deferred = Deferred.makeUnsafe<unknown, unknown>()
+    const deferred = Deferred.makeUnsafe<Value, unknown>()
    const promise = yield* ctx.pending.createWithSelf((self) =>
      Effect.flatMap(Deferred.await(deferred), (value) => resolvePromiseValue(ctx, value, self)),
    )
@@ -262,10 +262,10 @@ const settleAfterTurn = <A, E, R>(body: Effect.Effect<A, E, R>): Effect.Effect<A
  Effect.flatMap(Effect.exit(body), (exit) => Effect.andThen(Effect.yieldNow, exit))

 class PromiseAnyFulfilled {
-  constructor(readonly value: unknown) {}
+  constructor(readonly value: Value) {}
 }

-const reactionHandler = (value: unknown, method: string): Callable | undefined => {
+const reactionHandler = (value: Value, method: string): Callable | undefined => {
  if (isSupportedCallback(value)) return value
  if (typeofValue(value) === "function") {
    throw typeError(
@@ -279,7 +279,7 @@ const reactionHandler = (value: unknown, method: string): Callable | undefined =
 const reactionExit = <R>(
  ctx: Interpreter<R>,
  source: PromiseObj,
-): Effect.Effect<Exit.Exit<unknown, unknown>, unknown, R> =>
+): Effect.Effect<Exit.Exit<Value, unknown>, unknown, R> =>
  Effect.gen(function* () {
    const exit = yield* ctx.pending.await(source)
    if (!Exit.isSuccess(exit) && Cause.hasInterruptsOnly(exit.cause)) return yield* Effect.failCause(exit.cause)
@@ -1,47 +1,18 @@
 import { ToolReference } from "../tool-runtime.js"
 import { invalidData } from "./model.js"
-import {
-  Callable,
-  getOwn,
-  isWrapper,
-  ownKeys,
-  Arr,
-  Bytes,
-  DateObj,
-  GeneratorObj,
-  IteratorObj,
-  MapObj,
-  Obj,
-  PromiseObj,
-  RegExpObj,
-  SetObj,
-  URLObj,
-  URLSearchParamsObj,
-  HeadersObj,
-} from "./objects.js"
+import { Callable, getOwn, isRuntimeReference, Obj, Opaque, ownKeys, type Value } from "./objects.js"

-/** Values that cannot cross the data boundary. */
-export const isRuntimeReference = (value: unknown): boolean =>
-  value instanceof Callable ||
-  value instanceof GeneratorObj ||
-  value instanceof IteratorObj ||
-  value instanceof ToolReference ||
-  value instanceof PromiseObj ||
-  isWrapper(value)
-
-function* childValues(value: object): Generator {
-  if (!(value instanceof Obj)) return
-  for (const key of ownKeys(value)) yield getOwn(value, key)
-}
+/** Interpreter machinery that is never data, unlike a Date or Map, which cross some boundaries as copies. */
+export const isOpaque = (value: Value): boolean => value instanceof Opaque || value instanceof ToolReference

 // Depth-first search over a value tree. `match` stops the walk; `skip` prunes a subtree without matching it.
 const find = (
-  value: unknown,
-  match: (current: unknown) => boolean,
-  skip: (current: unknown) => boolean,
+  value: Value,
+  match: (current: Value) => boolean,
+  skip: (current: Value) => boolean,
  seen: Set<object>,
 ): boolean => {
-  const pending: Array<Iterator<unknown>> = [[value].values()]
+  const pending: Array<Iterator<Value>> = [[value].values()]
  while (pending.length > 0) {
    const next = pending.at(-1)!.next()
    if (next.done) {
@@ -50,25 +21,28 @@ const find = (
    }
    const current = next.value
    if (match(current)) return true
-    if (current === null || typeof current !== "object" || skip(current) || seen.has(current)) continue
+    if (!(current instanceof Obj) || skip(current) || seen.has(current)) continue
    seen.add(current)
-    pending.push(childValues(current))
+    pending.push(
+      ownKeys(current)
+        .map((key) => getOwn(current, key))
+        .values(),
+    )
  }
  return false
 }

 const never = () => false

-export const containsRuntimeReference = (value: unknown): boolean => find(value, isRuntimeReference, never, new Set())
+export const containsRuntimeReference = (value: Value): boolean => find(value, isRuntimeReference, never, new Set())

-// Wrapper values are data here, not opaque interpreter references.
-export const containsOpaqueReference = (value: unknown): boolean =>
-  find(value, (current) => !isWrapper(current) && isRuntimeReference(current), isWrapper, new Set())
+export const containsOpaqueReference = (value: Value): boolean =>
+  find(value, isOpaque, (current) => isRuntimeReference(current) && !isOpaque(current), new Set())

 // Reject cycles before mutation so later boundary walks remain safe.
 export const rejectCircularInsertion = (
-  container: object,
-  value: unknown,
+  container: Obj,
+  value: Value,
  label: string,
  seen = new Set<object>(),
 ): void => {
@@ -77,27 +51,14 @@ export const rejectCircularInsertion = (
  }
 }

-export const describeValue = (value: unknown): string => {
+export const describeValue = (value: Value): string => {
  if (value === null || value === undefined) return String(value)
-  if (value instanceof Arr) return "an array"
-  if (value instanceof PromiseObj) return "an un-awaited Promise"
+  if (value instanceof Obj) return value.describe
  if (value instanceof ToolReference) return "a tool reference"
-  if (value instanceof DateObj) return "a Date"
-  if (value instanceof RegExpObj) return "a RegExp"
-  if (value instanceof MapObj) return "a Map"
-  if (value instanceof SetObj) return "a Set"
-  if (value instanceof URLObj) return "a URL"
-  if (value instanceof URLSearchParamsObj) return "a URLSearchParams"
-  if (value instanceof HeadersObj) return "a Headers"
-  if (value instanceof Bytes) return "a Uint8Array"
-  if (value instanceof GeneratorObj) return "a generator"
-  if (value instanceof IteratorObj) return "an iterator"
-  if (isRuntimeReference(value)) return "a function"
-  if (typeof value === "object") return "a data object"
  return `a ${typeof value}`
 }

-export const typeofValue = (value: unknown): string => {
+export const typeofValue = (value: Value): string => {
  if (value instanceof Callable) return "function"
  if (value instanceof ToolReference) return value.path.length > 0 ? "function" : "object"
  return typeof value
@@ -1,4 +1,5 @@
 import { type AstNode, type Binding, referenceError, typeError } from "./model.js"
+import type { Value } from "./objects.js"

 export class ScopeStack {
  private readonly scopes: Array<Map<string, Binding>>
@@ -15,7 +16,7 @@ export class ScopeStack {
    scope.set(name, { mutable, value: undefined, initialized: false })
  }

-  initialize(name: string, value: unknown, node: AstNode): void {
+  initialize(name: string, value: Value, node: AstNode): void {
    const binding = this.current().get(name)
    if (!binding || binding.initialized !== false) {
      throw typeError(`Identifier '${name}' has not been reserved for initialization.`, node)
@@ -24,7 +25,7 @@ export class ScopeStack {
    binding.initialized = true
  }

-  declare(name: string, value: unknown, mutable: boolean, node: AstNode): void {
+  declare(name: string, value: Value, mutable: boolean, node: AstNode): void {
    const scope = this.current()
    if (scope.has(name)) {
      throw typeError(`Identifier '${name}' has already been declared.`, node)
@@ -32,7 +33,7 @@ export class ScopeStack {
    scope.set(name, { mutable, value, initialized: true })
  }

-  get(name: string, node: AstNode): unknown {
+  get(name: string, node: AstNode): Value {
    const binding = this.resolve(name)

    if (!binding) {
@@ -46,7 +47,7 @@ export class ScopeStack {
    return binding.value
  }

-  set(name: string, value: unknown, node: AstNode): unknown {
+  set(name: string, value: Value, node: AstNode): Value {
    const binding = this.resolve(name)

    if (!binding) {
@@ -2,14 +2,24 @@ import { Effect } from "effect"
 import { constructor, type Method, methods, prototypeFrom, receiver } from "../interpreter/native.js"
 import { checkArrayLength, checkStringLength, MAX_ARRAY_LENGTH } from "../interpreter/limits.js"
 import { invalidData, IteratorSymbol, rangeError, typeError } from "../interpreter/model.js"
-import { define, get, hidden, Arr, GeneratorObj, IteratorObj, Obj } from "../interpreter/objects.js"
+import {
+  define,
+  get,
+  hidden,
+  Arr,
+  GeneratorObj,
+  IteratorObj,
+  Obj,
+  coerceToNumber,
+  coerceToString,
+  type Value,
+} from "../interpreter/objects.js"
 import { describeValue, rejectCircularInsertion } from "../interpreter/references.js"
-import { applyCollectionCallback, preserveConsumerError } from "../interpreter/callback.js"
+import { applyCollectionCallback, invoke, preserveConsumerError } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
 import { compareText } from "../tool-runtime.js"
-import { coerceToNumber, coerceToString } from "./value.js"

-const arrayLikeSource = (source: unknown): { readonly length: number; readonly source: Obj } => {
+const arrayLikeSource = (source: Value): { readonly length: number; readonly source: Obj } => {
  if (source instanceof Obj && typeof get(source, "length") === "number") {
    const length = get(source, "length") as number
    const normalized = Number.isNaN(length) || length <= 0 ? 0 : Math.trunc(length)
@@ -21,7 +31,7 @@ const arrayLikeSource = (source: unknown): { readonly length: number; readonly s
  )
 }

-const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<unknown, unknown, R> => {
+const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<Value>): Effect.Effect<Value, unknown, R> => {
  const source = args[0]
  const proto = ctx.builtins.Array
  const apply =
@@ -33,14 +43,14 @@ const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<
        throw typeError("Array.from expects a synchronous iterable or array-like value.")
      }
      const arrayLike = arrayLikeSource(source)
-      const values: Array<unknown> = []
+      const values: Array<Value> = []
      for (let index = 0; index < arrayLike.length; index += 1) {
        const item = get(arrayLike.source, index)
        values.push(apply === undefined ? item : yield* apply([item, index]))
      }
      return new Arr(proto, values)
    }
-    const values: Array<unknown> = []
+    const values: Array<Value> = []
    let index = 0
    while (true) {
      const step = yield* cursor.next
@@ -53,21 +63,21 @@ const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<

 export const sortArray = <R>(
  ctx: Interpreter<R>,
-  target: Array<unknown>,
-  comparator: unknown,
+  target: Array<Value>,
+  comparator: Value,
  name: string,
-): Effect.Effect<Array<unknown>, unknown, R> => {
+): Effect.Effect<Array<Value>, unknown, R> => {
  if (comparator === undefined) {
    return Effect.sync(() => [...target].sort((a, b) => compareText(coerceToString(a), coerceToString(b))))
  }
  const apply = applyCollectionCallback(ctx, comparator, name)
-  const mergeSort = (items: Array<unknown>): Effect.Effect<Array<unknown>, unknown, R> => {
+  const mergeSort = (items: Array<Value>): Effect.Effect<Array<Value>, unknown, R> => {
    if (items.length <= 1) return Effect.succeed(items)
    const midpoint = Math.floor(items.length / 2)
    return Effect.gen(function* () {
      const left = yield* mergeSort(items.slice(0, midpoint))
      const right = yield* mergeSort(items.slice(midpoint))
-      const merged: Array<unknown> = []
+      const merged: Array<Value> = []
      let leftIndex = 0
      let rightIndex = 0
      while (leftIndex < left.length && rightIndex < right.length) {
@@ -88,8 +98,8 @@ export const sortArray = <R>(
 export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
  const proto = builtins.Array
-  const wrap = (items: Array<unknown>) => new Arr(proto, items)
-  const construct = (args: Array<unknown>, into: Obj): Arr => {
+  const wrap = (items: Array<Value>) => new Arr(proto, items)
+  const construct = (args: Array<Value>, into: Obj): Arr => {
    if (args.length !== 1) return new Arr(into, [...args])
    const first = args[0]
    if (typeof first !== "number") return new Arr(into, [first])
@@ -109,8 +119,8 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
    ["from", 1, (_, args) => arrayFrom(ctx, args)],
  ])

-  const self = (thisValue: unknown, name: string) => receiver(Arr, thisValue, `Array.prototype.${name}`)
-  const optNumber = (name: string, value: unknown, label: string): number | undefined => {
+  const self = (thisValue: Value, name: string) => receiver(Arr, thisValue, `Array.prototype.${name}`)
+  const optNumber = (name: string, value: Value, label: string): number | undefined => {
    if (value === undefined) return undefined
    if (typeof value !== "number") {
      throw typeError(`Array.${name} expects ${label} to be a number.`)
@@ -122,11 +132,11 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
    name: string,
    length: number,
    body: (
-      target: Array<unknown>,
+      target: Array<Value>,
      receiver: Arr,
-      apply: (args: Array<unknown>) => Effect.Effect<unknown, unknown, R>,
-      args: Array<unknown>,
-    ) => Effect.Effect<unknown, unknown, R>,
+      apply: (args: Array<Value>) => Effect.Effect<Value, unknown, R>,
+      args: Array<Value>,
+    ) => Effect.Effect<Value, unknown, R>,
  ): Method => [
    name,
    length,
@@ -214,7 +224,7 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
      "flat",
      0,
      (thisValue, args) => {
-        const flatten = (items: Array<unknown>, depth: number): Array<unknown> =>
+        const flatten = (items: Array<Value>, depth: number): Array<Value> =>
          items.flatMap((item) => (item instanceof Arr && depth > 0 ? flatten(item.items, depth - 1) : [item]))
        const flattened = flatten(self(thisValue, "flat").items, optNumber("flat", args[0], "depth") ?? 1)
        checkArrayLength(flattened.length)
@@ -340,6 +350,19 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
        return target
      },
    ],
+    [
+      "toLocaleString",
+      0,
+      (thisValue) =>
+        Effect.map(
+          Effect.forEach(self(thisValue, "toLocaleString").items, (item) =>
+            item === null || item === undefined
+              ? Effect.succeed("")
+              : Effect.map(invoke(ctx, item, "toLocaleString", "Array.prototype.toLocaleString"), coerceToString),
+          ),
+          (parts) => parts.join(","),
+        ),
+    ],
    ["keys", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "keys").items.keys())],
    ["values", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "values").items.values())],
    [
@@ -356,7 +379,7 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
    iterate("map", 1, (target, receiver, apply) =>
      Effect.gen(function* () {
        const length = target.length
-        const values: Array<unknown> = []
+        const values: Array<Value> = []
        values.length = length
        for (let index = 0; index < length; index += 1) {
          if (!(index in target)) continue
@@ -368,7 +391,7 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
    iterate("flatMap", 1, (target, receiver, apply) =>
      Effect.gen(function* () {
        const length = target.length
-        const values: Array<unknown> = []
+        const values: Array<Value> = []
        for (let index = 0; index < length; index += 1) {
          if (!(index in target)) continue
          const mapped = yield* apply([target[index], index, receiver])
@@ -381,7 +404,7 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
    iterate("filter", 1, (target, receiver, apply) =>
      Effect.gen(function* () {
        const length = target.length
-        const values: Array<unknown> = []
+        const values: Array<Value> = []
        for (let index = 0; index < length; index += 1) {
          if (!(index in target)) continue
          const item = target[index]
@@ -2,13 +2,24 @@ import { Effect } from "effect"
 import { checkArrayLength, checkStringLength } from "../interpreter/limits.js"
 import { constructor, methods, prototypeFrom, receiver, requiresNew } from "../interpreter/native.js"
 import { IteratorSymbol, rangeError, syntaxError, typeError } from "../interpreter/model.js"
-import { define, defineAccessor, get, hidden, Arr, Bytes, IteratorObj, Obj } from "../interpreter/objects.js"
+import {
+  define,
+  defineAccessor,
+  get,
+  hidden,
+  Arr,
+  Bytes,
+  IteratorObj,
+  Obj,
+  coerceToNumber,
+  coerceToString,
+  type Value,
+} from "../interpreter/objects.js"
 import { describeValue } from "../interpreter/references.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToNumber, coerceToString } from "./value.js"

 /** The bytes a Uint8Array, array, or other iterable of numbers describes; the host array clamps each value. */
-const collectBytes = <R>(ctx: Interpreter<R>, source: unknown, name: string): Effect.Effect<Uint8Array, unknown, R> => {
+const collectBytes = <R>(ctx: Interpreter<R>, source: Value, name: string): Effect.Effect<Uint8Array, unknown, R> => {
  if (source instanceof Bytes) return Effect.succeed(new Uint8Array(source.bytes))
  return Effect.gen(function* () {
    const cursor = yield* ctx.iterate(source)
@@ -27,7 +38,7 @@ const collectBytes = <R>(ctx: Interpreter<R>, source: unknown, name: string): Ef
  })
 }

-const constructBytes = <R>(ctx: Interpreter<R>, args: Array<unknown>, proto: Obj) => {
+const constructBytes = <R>(ctx: Interpreter<R>, args: Array<Value>, proto: Obj) => {
  const source = args[0]
  if (source !== null && typeof source === "object") {
    return Effect.map(collectBytes(ctx, source, "new Uint8Array(...)"), (bytes) => new Bytes(proto, bytes))
@@ -48,7 +59,7 @@ export const uint8ArrayGlobal = <R>(ctx: Interpreter<R>) => {
    call: requiresNew("Uint8Array"),
    construct: (args, newTarget) => constructBytes(ctx, args, prototypeFrom(newTarget, proto)),
  })
-  const decode = (name: string, args: Array<unknown>, from: (text: string) => Uint8Array) => {
+  const decode = (name: string, args: Array<Value>, from: (text: string) => Uint8Array) => {
    if (typeof args[0] !== "string") throw typeError(`Uint8Array.${name} expects a string.`)
    try {
      return wrap(from(args[0]))
@@ -63,13 +74,13 @@ export const uint8ArrayGlobal = <R>(ctx: Interpreter<R>) => {
    ["fromHex", 1, (_, args) => decode("fromHex", args, (text) => Uint8Array.fromHex(text))],
  ])

-  const self = (thisValue: unknown, name: string) => receiver(Bytes, thisValue, `Uint8Array.prototype.${name}`)
-  const optNumber = (name: string, value: unknown, label: string): number | undefined => {
+  const self = (thisValue: Value, name: string) => receiver(Bytes, thisValue, `Uint8Array.prototype.${name}`)
+  const optNumber = (name: string, value: Value, label: string): number | undefined => {
    if (value === undefined) return undefined
    if (typeof value !== "number") throw typeError(`Uint8Array.${name} expects ${label} to be a number.`)
    return value
  }
-  const wrapAll = (items: Array<unknown>) => new Arr(builtins.Array, items)
+  const wrapAll = (items: Array<Value>) => new Arr(builtins.Array, items)
  defineAccessor(proto, "length", (thisValue) => self(thisValue, "length").bytes.length)
  methods(builtins, proto, [
    ["at", 1, (thisValue, args) => self(thisValue, "at").bytes.at(optNumber("at", args[0], "index") ?? 0)],
@@ -222,8 +233,7 @@ const utf8Labels = new Set(["unicode-1-1-utf-8", "unicode11utf8", "unicode20utf8
 export const textDecoderGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
  const proto = builtins.TextDecoder
-  const self = (thisValue: unknown, name: string) =>
-    receiver(TextDecoderObj, thisValue, `TextDecoder.prototype.${name}`)
+  const self = (thisValue: Value, name: string) => receiver(TextDecoderObj, thisValue, `TextDecoder.prototype.${name}`)
  defineAccessor(proto, "encoding", (thisValue) => self(thisValue, "encoding").decoder.encoding)
  defineAccessor(proto, "fatal", (thisValue) => self(thisValue, "fatal").decoder.fatal)
  defineAccessor(proto, "ignoreBOM", (thisValue) => self(thisValue, "ignoreBOM").decoder.ignoreBOM)
@@ -7,15 +7,16 @@ import {
  get,
  getOwn,
  hidden,
-  isWrapper,
  Arr,
+  coerceToString,
  IteratorObj,
  MapObj,
  Obj,
  PromiseObj,
  SetObj,
+  type Value,
 } from "../interpreter/objects.js"
-import { describeValue, isRuntimeReference } from "../interpreter/references.js"
+import { describeValue, isOpaque } from "../interpreter/references.js"
 import {
  applyCollectionCallback,
  isSupportedCallback,
@@ -25,9 +26,9 @@ import {
 } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"

-const coerceGroupByPropertyKey = <R>(ctx: Interpreter<R>, value: unknown): Effect.Effect<string, unknown, R> => {
-  if (value instanceof PromiseObj) return Effect.succeed("[object Promise]")
-  if (!isWrapper(value) && isRuntimeReference(value)) {
+const coerceGroupByPropertyKey = <R>(ctx: Interpreter<R>, value: Value): Effect.Effect<string, unknown, R> => {
+  if (value instanceof PromiseObj) return Effect.succeed(coerceToString(value))
+  if (isOpaque(value)) {
    throw invalidData(`Object.groupBy callback must return a data value, received ${describeValue(value)}.`)
  }
  return toPrimitiveString(ctx, value)
@@ -81,7 +82,7 @@ export const groupBy = <R>(ctx: Interpreter<R>, namespace: "Map" | "Object") =>
    })
  })

-const constructMap = <R>(ctx: Interpreter<R>, init: unknown, proto: Obj) => {
+const constructMap = <R>(ctx: Interpreter<R>, init: Value, proto: Obj) => {
  const target = new MapObj(proto)
  if (init === undefined || init === null) return Effect.succeed(target)
  return Effect.gen(function* () {
@@ -105,7 +106,7 @@ const constructMap = <R>(ctx: Interpreter<R>, init: unknown, proto: Obj) => {
  })
 }

-const constructSet = <R>(ctx: Interpreter<R>, init: unknown, proto: Obj) => {
+const constructSet = <R>(ctx: Interpreter<R>, init: Value, proto: Obj) => {
  const target = new SetObj(proto)
  if (init === undefined || init === null) return Effect.succeed(target)
  return Effect.gen(function* () {
@@ -130,8 +131,7 @@ export const mapGlobal = <R>(ctx: Interpreter<R>) => {
    construct: (args, newTarget) => constructMap(ctx, args[0], prototypeFrom(newTarget, proto)),
  })
  define(map, "groupBy", groupBy(ctx, "Map"), hidden)
-  const self = (thisValue: unknown, name: string) => receiver(MapObj, thisValue, `Map.prototype.${name}`)
-  const wrap = (items: Array<unknown>) => new Arr(builtins.Array, items)
+  const self = (thisValue: Value, name: string) => receiver(MapObj, thisValue, `Map.prototype.${name}`)
  defineAccessor(proto, "size", (thisValue) => receiver(MapObj, thisValue, "Map.prototype.size").map.size)
  methods(builtins, proto, [
    ["get", 1, (thisValue, args) => self(thisValue, "get").map.get(args[0])],
@@ -145,6 +145,29 @@ export const mapGlobal = <R>(ctx: Interpreter<R>) => {
        return target
      },
    ],
+    [
+      "getOrInsert",
+      2,
+      (thisValue, args) => {
+        const target = self(thisValue, "getOrInsert").map
+        if (!target.has(args[0])) target.set(args[0], args[1])
+        return target.get(args[0])
+      },
+    ],
+    [
+      "getOrInsertComputed",
+      2,
+      (thisValue, args) => {
+        const target = self(thisValue, "getOrInsertComputed").map
+        const apply = applyCollectionCallback(ctx, args[1], "Map.getOrInsertComputed")
+        if (target.has(args[0])) return target.get(args[0])
+        // The callback sees the stored key (-0 is +0) and its result wins over anything it inserted itself.
+        return Effect.map(apply([args[0] === 0 ? 0 : args[0]]), (value) => {
+          target.set(args[0], value)
+          return value
+        })
+      },
+    ],
    ["delete", 1, (thisValue, args) => self(thisValue, "delete").map.delete(args[0])],
    [
      "clear",
@@ -156,17 +179,7 @@ export const mapGlobal = <R>(ctx: Interpreter<R>) => {
    ],
    ["keys", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "keys").map.keys())],
    ["values", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "values").map.values())],
-    [
-      "entries",
-      0,
-      (thisValue) =>
-        new IteratorObj(
-          builtins.Iterator,
-          self(thisValue, "entries")
-            .map.entries()
-            .map(([key, item]) => wrap([key, item])),
-        ),
-    ],
+    ["entries", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "entries").iterator(builtins))],
    [
      "forEach",
      1,
@@ -186,26 +199,26 @@ export const mapGlobal = <R>(ctx: Interpreter<R>) => {

 type SetRecord<R> = {
  readonly size: number
-  readonly has: (item: unknown) => Effect.Effect<boolean, unknown, R>
-  readonly keys: () => Effect.Effect<Iterable<unknown>, unknown, R>
+  readonly has: (item: Value) => Effect.Effect<boolean, unknown, R>
+  readonly keys: () => Effect.Effect<Iterable<Value>, unknown, R>
 }

 const loadSetRecord = <R>(
  ctx: Interpreter<R>,
-  source: unknown,
+  source: Value,
  name: string,
 ): Effect.Effect<SetRecord<R>, unknown, R> => {
  if (source instanceof SetObj) {
    return Effect.succeed({
      size: source.set.size,
-      has: (item: unknown) => Effect.succeed(source.set.has(item)),
+      has: (item: Value) => Effect.succeed(source.set.has(item)),
      keys: () => Effect.succeed(source.set.values()),
    })
  }
  if (source instanceof MapObj) {
    return Effect.succeed({
      size: source.map.size,
-      has: (item: unknown) => Effect.succeed(source.map.has(item)),
+      has: (item: Value) => Effect.succeed(source.map.has(item)),
      keys: () => Effect.succeed(source.map.keys()),
    })
  }
@@ -224,10 +237,10 @@ const loadSetRecord = <R>(
    }
    return {
      size: Math.max(Math.trunc(size), 0),
-      has: (item: unknown) => Effect.map(ctx.call(has, source, [item]), Boolean),
+      has: (item: Value) => Effect.map(ctx.call(has, source, [item]), Boolean),
      keys: () =>
-        Effect.flatMap(ctx.call(keys, source, []), (result): Effect.Effect<Iterable<unknown>> => {
-          if (result instanceof IteratorObj) return Effect.succeed(result.iterator)
+        Effect.flatMap(ctx.call(keys, source, []), (result): Effect.Effect<Iterable<Value>> => {
+          if (result instanceof IteratorObj) return Effect.succeed(result.source)
          if (result instanceof Arr) return Effect.succeed(result.items)
          throw typeError(`Set.${name} expected 'keys' to return an iterator.`)
        }),
@@ -239,8 +252,8 @@ const setOperation = <R>(
  ctx: Interpreter<R>,
  target: SetObj,
  name: string,
-  source: unknown,
-): Effect.Effect<unknown, unknown, R> =>
+  source: Value,
+): Effect.Effect<Value, unknown, R> =>
  Effect.gen(function* () {
    const other = yield* loadSetRecord(ctx, source, name)
    const copy = () => {
@@ -319,8 +332,8 @@ export const setGlobal = <R>(ctx: Interpreter<R>) => {
    call: requiresNew("Set"),
    construct: (args, newTarget) => constructSet(ctx, args[0], prototypeFrom(newTarget, proto)),
  })
-  const self = (thisValue: unknown, name: string) => receiver(SetObj, thisValue, `Set.prototype.${name}`)
-  const wrap = (items: Array<unknown>) => new Arr(builtins.Array, items)
+  const self = (thisValue: Value, name: string) => receiver(SetObj, thisValue, `Set.prototype.${name}`)
+  const wrap = (items: Array<Value>) => new Arr(builtins.Array, items)
  const operation = (name: string): Method => [
    name,
    1,
@@ -1,22 +1,8 @@
 import { type Method, methods } from "../interpreter/native.js"
-import {
-  entries,
-  get,
-  Arr,
-  Bytes,
-  DateObj,
-  MapObj,
-  Obj,
-  PromiseObj,
-  RegExpObj,
-  SetObj,
-  URLObj,
-  URLSearchParamsObj,
-  HeadersObj,
-} from "../interpreter/objects.js"
-import { containsOpaqueReference, isRuntimeReference } from "../interpreter/references.js"
+import { entries, get, Arr, Obj, type Value } from "../interpreter/objects.js"
+import { ToolReference } from "../tool-runtime.js"
+import { containsOpaqueReference } from "../interpreter/references.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToString } from "./value.js"

 const consoleMethods = ["log", "info", "debug", "warn", "error", "dir", "table"]

@@ -43,7 +29,7 @@ export const consoleGlobal = <R>(ctx: Interpreter<R>) => {

 const MAX_CONSOLE_DEPTH = 32

-const formatConsoleMessage = (name: string, args: Array<unknown>): string => {
+const formatConsoleMessage = (name: string, args: Array<Value>): string => {
  if (name === "dir") return args.length === 0 ? "undefined" : formatValue(args[0])
  if (name === "table") return formatConsoleTable(args[0], args[1])
  const prefix = name === "warn" ? "[warn] " : name === "error" ? "[error] " : name === "debug" ? "[debug] " : ""
@@ -51,60 +37,27 @@ const formatConsoleMessage = (name: string, args: Array<unknown>): string => {
 }

 /** One value as `console.log` shows it. */
-export const formatValue = (value: unknown): string => {
+export const formatValue = (value: Value): string => {
  if (value === undefined) return "undefined"
  if (typeof value === "string") return value
  return formatConsoleValue(value, new Set(), 0)
 }

-const formatConsoleValue = (value: unknown, seen: Set<object>, depth: number): string => {
+const formatConsoleValue = (value: Value, seen: Set<object>, depth: number): string => {
  if (value === null || value === undefined) return "null"
  if (typeof value === "string") return JSON.stringify(value)
-  if (typeof value === "number" || typeof value === "boolean") return String(value)
-  if (typeof value !== "object") return String(value)
-  if (value instanceof PromiseObj) return "[Promise (await it to get its value)]"
-  if (value instanceof DateObj) return coerceToString(value)
-  if (value instanceof RegExpObj) return coerceToString(value)
-  if (value instanceof URLObj) return coerceToString(value)
-  if (value instanceof URLSearchParamsObj) return coerceToString(value)
-  if (value instanceof HeadersObj) return `Headers ${JSON.stringify(Object.fromEntries(value.headers))}`
-  if (value instanceof Bytes) return `Uint8Array(${value.bytes.length}) [${value.bytes.join(",")}]`
+  if (!(value instanceof Obj)) return value instanceof ToolReference ? "[opaque reference]" : String(value)
  if (depth > MAX_CONSOLE_DEPTH) return "..."
  if (seen.has(value)) return "[Circular]"
-  if (value instanceof MapObj) {
-    seen.add(value)
-    try {
-      const items = Array.from(value.map.entries(), ([key, item]) => `[${formatItems([key, item], seen, depth + 1)}]`)
-      return `Map(${value.map.size}) [${items.join(",")}]`
-    } finally {
-      seen.delete(value)
-    }
-  }
-  if (value instanceof SetObj) {
-    seen.add(value)
-    try {
-      return `Set(${value.set.size}) [${formatItems([...value.set.values()], seen, depth + 1)}]`
-    } finally {
-      seen.delete(value)
-    }
-  }
-  if (isRuntimeReference(value)) return "[opaque reference]"
  seen.add(value)
  try {
-    if (value instanceof Arr) return `[${formatItems(value.items, seen, depth + 1)}]`
-    if (!(value instanceof Obj)) return "[object Object]"
-    return `{${entries(value)
-      .map(([key, item]) => `${JSON.stringify(key)}:${formatConsoleValue(item, seen, depth + 1)}`)
-      .join(",")}}`
+    return value.inspect((item) => formatConsoleValue(item, seen, depth + 1))
  } finally {
    seen.delete(value)
  }
 }

-const formatItems = (items: Array<unknown>, seen: Set<object>, depth: number): string =>
-  items.map((item) => formatConsoleValue(item, seen, depth)).join(",")
-
-const formatConsoleTable = (value: unknown, columnsArgument: unknown): string => {
+const formatConsoleTable = (value: Value, columnsArgument: Value): string => {
  if (value === undefined) return "undefined"
  if (containsOpaqueReference(value)) return "[opaque reference]"
  const columns = columnsArgument instanceof Arr ? columnsArgument.items.map(String) : undefined
@@ -118,9 +71,9 @@ const formatConsoleTable = (value: unknown, columnsArgument: unknown): string =>
 }

 const consoleTableRows = (
-  data: unknown,
+  data: Value,
  columns: ReadonlyArray<string> | undefined,
-): Array<{ readonly index: string; readonly values: Record<string, unknown> }> => {
+): Array<{ readonly index: string; readonly values: Record<string, Value> }> => {
  if (data instanceof Arr) {
    return data.items.map((item, index) => ({ index: String(index), values: consoleTableValues(item, columns) }))
  }
@@ -130,7 +83,7 @@ const consoleTableRows = (
  return [{ index: "0", values: { Value: data } }]
 }

-const consoleTableValues = (value: unknown, columns: ReadonlyArray<string> | undefined): Record<string, unknown> => {
+const consoleTableValues = (value: Value, columns: ReadonlyArray<string> | undefined): Record<string, Value> => {
  if (value instanceof Obj && !(value instanceof Arr)) {
    if (columns !== undefined) return Object.fromEntries(columns.map((column) => [column, get(value, column)]))
    return Object.fromEntries(entries(value))
@@ -138,7 +91,7 @@ const consoleTableValues = (value: unknown, columns: ReadonlyArray<string> | und
  return { Value: value }
 }

-const formatConsoleTableCell = (value: unknown): string => {
+const formatConsoleTableCell = (value: Value): string => {
  if (value === undefined) return ""
  if (typeof value === "string") return value
  return formatConsoleValue(value, new Set(), 0)
@@ -1,12 +1,11 @@
 import { Effect } from "effect"
 import { constructor, type Method, methods, prototypeFrom, receiver } from "../interpreter/native.js"
 import { rangeError } from "../interpreter/model.js"
-import { DateObj, Obj } from "../interpreter/objects.js"
+import { DateObj, Obj, coerceToNumber, coerceToString, type Value } from "../interpreter/objects.js"
 import { toPrimitive, toPrimitiveNumber } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToNumber, coerceToString } from "./value.js"

-const constructDate = <R>(ctx: Interpreter<R>, args: Array<unknown>, proto: Obj) => {
+const constructDate = <R>(ctx: Interpreter<R>, args: Array<Value>, proto: Obj) => {
  if (args.length === 0) return Effect.succeed(new DateObj(proto, Date.now()))
  if (args.length === 1) {
    const arg = args[0]
@@ -83,7 +82,7 @@ export const dateGlobal = <R>(ctx: Interpreter<R>) => {
    ["UTC", 7, (_, args) => Date.UTC(...(args.map((arg) => coerceToNumber(arg)) as Parameters<typeof Date.UTC>))],
  ])

-  const self = (thisValue: unknown, name: string) => receiver(DateObj, thisValue, `Date.prototype.${name}`)
+  const self = (thisValue: Value, name: string) => receiver(DateObj, thisValue, `Date.prototype.${name}`)
  const iso = (value: DateObj) => {
    if (!Number.isFinite(value.time)) throw rangeError("Invalid time value.")
    return new Date(value.time).toISOString()
@@ -105,6 +104,13 @@ export const dateGlobal = <R>(ctx: Interpreter<R>) => {
    ["toTimeString", 0, (thisValue) => new Date(self(thisValue, "toTimeString").time).toTimeString()],
    ["toUTCString", 0, (thisValue) => new Date(self(thisValue, "toUTCString").time).toUTCString()],
    ["toGMTString", 0, (thisValue) => new Date(self(thisValue, "toGMTString").time).toUTCString()],
+    ...(["toLocaleString", "toLocaleDateString", "toLocaleTimeString"] as const).map(
+      (name): Method => [
+        name,
+        0,
+        (thisValue) => new Date(self(thisValue, name).time)[name]("en-US", { timeZone: "UTC" }),
+      ],
+    ),
    ...getters.map((name): Method => [name, 0, (thisValue) => new Date(self(thisValue, name).time)[name]()]),
    ...setters.map(
      ([name, length]): Method => [
@@ -1,11 +1,21 @@
 import { Effect } from "effect"
 import { constructor, methods, prototypeFrom, receiver, requiresNew } from "../interpreter/native.js"
 import { IteratorSymbol, typeError } from "../interpreter/model.js"
-import { define, entries, get, hidden, Arr, HeadersObj, IteratorObj, Obj } from "../interpreter/objects.js"
+import {
+  define,
+  entries,
+  get,
+  hidden,
+  Arr,
+  HeadersObj,
+  IteratorObj,
+  Obj,
+  coerceToString,
+  isRuntimeReference,
+  type Value,
+} from "../interpreter/objects.js"
 import { applyCollectionCallback } from "../interpreter/callback.js"
-import { isRuntimeReference } from "../interpreter/references.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToString } from "./value.js"
 import { readPairs } from "./url.js"

 // The host validates header names and values and throws its own TypeError; the program gets one of its own.
@@ -17,7 +27,7 @@ const attempt = <T>(run: () => T): T => {
  }
 }

-const constructHeaders = <R>(ctx: Interpreter<R>, init: unknown, proto: Obj): Effect.Effect<HeadersObj, unknown, R> => {
+const constructHeaders = <R>(ctx: Interpreter<R>, init: Value, proto: Obj): Effect.Effect<HeadersObj, unknown, R> => {
  const wrap = (headers: Headers) => new HeadersObj(proto, headers)
  if (init === undefined) return Effect.succeed(wrap(new Headers()))
  return Effect.gen(function* () {
@@ -40,10 +50,10 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
    call: requiresNew("Headers"),
    construct: (args, newTarget) => constructHeaders(ctx, args[0], prototypeFrom(newTarget, proto)),
  })
-  const self = (thisValue: unknown, name: string) => receiver(HeadersObj, thisValue, `Headers.prototype.${name}`)
-  const wrap = (items: Array<unknown>) => new Arr(builtins.Array, items)
-  const arg = (args: Array<unknown>, index: number): string => coerceToString(args[index])
-  const requireArgs = (name: string, args: Array<unknown>, count: number): void => {
+  const self = (thisValue: Value, name: string) => receiver(HeadersObj, thisValue, `Headers.prototype.${name}`)
+  const wrap = (items: Array<Value>) => new Arr(builtins.Array, items)
+  const arg = (args: Array<Value>, index: number): string => coerceToString(args[index])
+  const requireArgs = (name: string, args: Array<Value>, count: number): void => {
    if (args.length < count) throw typeError(`Headers.${name} requires ${count} argument${count === 1 ? "" : "s"}.`)
  }
  methods(builtins, proto, [
@@ -53,7 +63,8 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
      (thisValue, args) => {
        requireArgs("append", args, 2)
        const target = self(thisValue, "append").headers
-        return attempt(() => target.append(arg(args, 0), arg(args, 1)))
+        attempt(() => target.append(arg(args, 0), arg(args, 1)))
+        return undefined
      },
    ],
    [
@@ -62,7 +73,8 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
      (thisValue, args) => {
        requireArgs("delete", args, 1)
        const target = self(thisValue, "delete").headers
-        return attempt(() => target.delete(arg(args, 0)))
+        attempt(() => target.delete(arg(args, 0)))
+        return undefined
      },
    ],
    [
@@ -90,7 +102,8 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
      (thisValue, args) => {
        requireArgs("set", args, 2)
        const target = self(thisValue, "set").headers
-        return attempt(() => target.set(arg(args, 0), arg(args, 1)))
+        attempt(() => target.set(arg(args, 0), arg(args, 1)))
+        return undefined
      },
    ],
    // Iterator.from because Bun's Headers typings predate iterator helpers; the runtime iterators already have them.
@@ -104,15 +117,7 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
      0,
      (thisValue) => new IteratorObj(builtins.Iterator, Iterator.from(self(thisValue, "values").headers.values())),
    ],
-    [
-      "entries",
-      0,
-      (thisValue) =>
-        new IteratorObj(
-          builtins.Iterator,
-          Iterator.from(self(thisValue, "entries").headers.entries()).map(([key, value]) => wrap([key, value])),
-        ),
-    ],
+    ["entries", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "entries").iterator(builtins))],
    [
      "forEach",
      1,
@@ -11,7 +11,7 @@ export const iteratorGlobals = <R>(ctx: Interpreter<R>): void => {
      "next",
      0,
      (thisValue) => {
-        const step = receiver(IteratorObj, thisValue, "Iterator.prototype.next").iterator.next()
+        const step = receiver(IteratorObj, thisValue, "Iterator.prototype.next").source.next()
        return record(builtins.Object, { value: step.value, done: Boolean(step.done) })
      },
    ],
@@ -6,7 +6,7 @@ import { checkStringLength } from "../interpreter/limits.js"
 import { syntaxError, typeError } from "../interpreter/model.js"
 import { typeofValue } from "../interpreter/references.js"
 import { fromJson, toJson } from "../data.js"
-import { get, keys, Arr, Obj, record, remove, set } from "../interpreter/objects.js"
+import { get, keys, Arr, Obj, record, remove, set, type Value } from "../interpreter/objects.js"

 export const jsonGlobal = <R>(ctx: Interpreter<R>) => {
  const json = new Obj(ctx.builtins.Object)
@@ -17,7 +17,7 @@ export const jsonGlobal = <R>(ctx: Interpreter<R>) => {
  return json
 }

-const parse = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<unknown, unknown, R> => {
+const parse = <R>(ctx: Interpreter<R>, args: Array<Value>): Effect.Effect<Value, unknown, R> => {
  const text = args[0]
  if (typeof text !== "string") throw typeError("JSON.parse expects a string.")

@@ -31,7 +31,7 @@ const parse = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<unkn
  if (typeofValue(args[1]) !== "function") return Effect.succeed(parsed)

  const apply = applyCollectionCallback(ctx, args[1], "JSON.parse")
-  const visit = (holder: Obj, key: string): Effect.Effect<unknown, unknown, R> =>
+  const visit = (holder: Obj, key: string): Effect.Effect<Value, unknown, R> =>
    Effect.gen(function* () {
      const value = get(holder, key)
      if (value instanceof Obj) {
@@ -46,7 +46,7 @@ const parse = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<unkn
  return visit(record(ctx.builtins.Object, { "": parsed }), "")
 }

-const stringify = <R>(ctx: Interpreter<R>, args: Array<unknown>): Effect.Effect<unknown, unknown, R> => {
+const stringify = <R>(ctx: Interpreter<R>, args: Array<Value>): Effect.Effect<Value, unknown, R> => {
  const space = args[2]
  const indent = typeof space === "number" || typeof space === "string" ? space : undefined
  const replacer = args[1]
@@ -1,7 +1,7 @@
 import { Effect } from "effect"
 import { constants, type Method, methods } from "../interpreter/native.js"
 import { typeError } from "../interpreter/model.js"
-import { Obj } from "../interpreter/objects.js"
+import { Obj, type Value } from "../interpreter/objects.js"
 import { preserveConsumerError } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"

@@ -14,7 +14,7 @@ declare global {

 // Validate only the arguments a method consumes; like JS, extras are ignored
 // (so built-ins work as callbacks receiving (element, index, array)).
-const number = (name: string, args: Array<unknown>, index: number): number => {
+const number = (name: string, args: Array<Value>, index: number): number => {
  if (index >= args.length) return Number.NaN
  const arg = args[index]
  if (typeof arg !== "number") throw typeError(`Math.${name} expects number arguments.`)
@@ -1,7 +1,8 @@
 import { constructor, constants, methods } from "../interpreter/native.js"
+import { coerceToString, type Value } from "../interpreter/objects.js"
 import { rangeError, typeError } from "../interpreter/model.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coercion, coerceToString } from "./value.js"
+import { coercion } from "./value.js"

 export const numberGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
@@ -39,17 +40,18 @@ export const numberGlobal = <R>(ctx: Interpreter<R>) => {
    ["parseFloat", 1, (_, args) => parseFloat(coerceToString(args[0]))],
  ])

-  const self = (thisValue: unknown, name: string): number => {
+  const self = (thisValue: Value, name: string): number => {
    if (typeof thisValue === "number") return thisValue
    throw typeError(`Number.prototype.${name} requires that 'this' be a Number.`)
  }
-  const optNum = (name: string, arg: unknown): number | undefined => {
+  const optNum = (name: string, arg: Value): number | undefined => {
    if (arg === undefined) return undefined
    if (typeof arg !== "number") throw typeError(`Number.${name} expects a number argument.`)
    return arg
  }
  methods(builtins, builtins.Number, [
    ["toFixed", 1, (thisValue, args) => self(thisValue, "toFixed").toFixed(optNum("toFixed", args[0]))],
+    ["toLocaleString", 0, (thisValue) => self(thisValue, "toLocaleString").toLocaleString("en-US")],
    [
      "toExponential",
      1,
@@ -88,7 +90,7 @@ export const booleanGlobal = <R>(ctx: Interpreter<R>) => {
    length: 1,
    call: coercion(ctx, "Boolean").call,
  })
-  const self = (thisValue: unknown, name: string): boolean => {
+  const self = (thisValue: Value, name: string): boolean => {
    if (typeof thisValue === "boolean") return thisValue
    throw typeError(`Boolean.prototype.${name} requires that 'this' be a Boolean.`)
  }
@@ -9,7 +9,6 @@ import {
  typeError,
 } from "../interpreter/model.js"
 import {
-  Callable,
  define,
  entries,
  enumerableKeys,
@@ -20,23 +19,20 @@ import {
  keys,
  own,
  Arr,
-  Bytes,
-  DateObj,
-  ErrorObj,
  Obj,
  PromiseObj,
-  RegExpObj,
  set,
+  coerceToString,
+  type Value,
 } from "../interpreter/objects.js"
 import { containsOpaqueReference, describeValue, rejectCircularInsertion } from "../interpreter/references.js"
-import { preserveConsumerError } from "../interpreter/callback.js"
+import { invoke, preserveConsumerError } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
 import { ToolReference } from "../tool-runtime.js"
 import { groupBy } from "./collections.js"
-import { coerceToString } from "./value.js"

 // ToObject for enumeration.
-export const enumerableSource = <R>(ctx: Interpreter<R>, label: string, value: unknown, node?: AstNode): Obj => {
+export const enumerableSource = <R>(ctx: Interpreter<R>, label: string, value: Value, node?: AstNode): Obj => {
  if (value === null || value === undefined) {
    throw typeError(`${label} cannot convert ${describeValue(value)} to an object.`, node)
  }
@@ -54,7 +50,7 @@ export const enumerableSource = <R>(ctx: Interpreter<R>, label: string, value: u
  return new Obj(ctx.builtins.Object)
 }

-export const objectAssign = <R>(ctx: Interpreter<R>, args: Array<unknown>): unknown => {
+export const objectAssign = <R>(ctx: Interpreter<R>, args: Array<Value>): Value => {
  const target = args[0]
  // JS would box a primitive target; wrappers and primitives cannot hold fields here.
  if (!(target instanceof Obj)) {
@@ -75,7 +71,7 @@ export const objectAssign = <R>(ctx: Interpreter<R>, args: Array<unknown>): unkn
  return target
 }

-const objectFromEntries = <R>(ctx: Interpreter<R>, source: unknown): Effect.Effect<Obj, unknown, R> => {
+const objectFromEntries = <R>(ctx: Interpreter<R>, source: Value): Effect.Effect<Obj, unknown, R> => {
  const out = new Obj(ctx.builtins.Object)
  return Effect.gen(function* () {
    const cursor = yield* ctx.iterate(source)
@@ -98,29 +94,24 @@ const objectFromEntries = <R>(ctx: Interpreter<R>, source: unknown): Effect.Effe
  })
 }

-export const classTag = (value: unknown): string => {
+const classTag = (value: Value): string => {
  if (value === null) return "Null"
  if (value === undefined) return "Undefined"
-  if (value instanceof Arr) return "Array"
-  if (value instanceof Callable) return "Function"
-  if (value instanceof ErrorObj) return "Error"
-  if (value instanceof DateObj) return "Date"
-  if (value instanceof RegExpObj) return "RegExp"
-  if (value instanceof Bytes) return "Uint8Array"
+  if (value instanceof Obj) return value.tag
  if (typeof value === "string") return "String"
  if (typeof value === "number") return "Number"
  if (typeof value === "boolean") return "Boolean"
  return "Object"
 }

-const propertyKey = (value: unknown): PropertyKey =>
+const propertyKey = (value: Value): PropertyKey =>
  value === AsyncIteratorSymbol || value === IteratorSymbol ? value : coerceToString(value)

 // Object constructs identically with or without new, like JS. Only `keys` copies its result into the
 // program; `values`, `entries`, `assign`, and `fromEntries` hand back the program's own values.
 export const objectGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
-  const construct = (args: Array<unknown>): unknown => {
+  const construct = (args: Array<Value>): Value => {
    const first = args[0]
    if (first === null || first === undefined) return new Obj(builtins.Object)
    if (first instanceof Obj) return first
@@ -196,7 +187,7 @@ export const objectGlobal = <R>(ctx: Interpreter<R>) => {
        true,
    ],
    ["toString", 0, (thisValue) => `[object ${classTag(thisValue)}]`],
-    ["toLocaleString", 0, (thisValue) => `[object ${classTag(thisValue)}]`],
+    ["toLocaleString", 0, (thisValue) => invoke(ctx, thisValue, "toString", "Object.prototype.toLocaleString")],
    [
      "valueOf",
      0,
@@ -2,9 +2,18 @@ import { Effect } from "effect"
 import type { Builtins } from "../interpreter/intrinsics.js"
 import { constructor, type Method, methods, prototypeFrom, receiver } from "../interpreter/native.js"
 import { syntaxError, typeError } from "../interpreter/model.js"
-import { define, defineAccessor, Arr, Obj, RegExpObj, record } from "../interpreter/objects.js"
+import {
+  define,
+  defineAccessor,
+  Arr,
+  Obj,
+  RegExpObj,
+  record,
+  coerceToNumber,
+  coerceToString,
+  type Value,
+} from "../interpreter/objects.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToNumber, coerceToString } from "./value.js"

 const flagProperties = [
  "hasIndices",
@@ -23,7 +32,7 @@ const regexFailureReason = (error: unknown): string =>
 const escapeRegexHint =
  'To match special characters like ( ) [ ] { } + * ? . literally, escape them with a backslash (e.g. "\\\\(") or test for them with String.includes instead.'

-export const toHostRegex = (arg: unknown, method: string, extraFlags = ""): RegExp => {
+export const toHostRegex = (arg: Value, method: string, extraFlags = ""): RegExp => {
  // Native parity: an undefined pattern behaves as an empty pattern.
  if (arg === undefined) return new RegExp("", extraFlags)
  if (arg instanceof RegExpObj) return arg.regex
@@ -53,7 +62,7 @@ export const matchToValue = (builtins: Builtins, match: RegExpMatchArray): Arr =
  return result
 }

-export const constructRegExp = (builtins: Builtins, args: Array<unknown>, proto: Obj = builtins.RegExp): RegExpObj => {
+export const constructRegExp = (builtins: Builtins, args: Array<Value>, proto: Obj = builtins.RegExp): RegExpObj => {
  const first = args[0]
  const pattern = first instanceof RegExpObj ? first.regex.source : first === undefined ? "" : coerceToString(first)
  const flagsArg = args[1]
@@ -96,7 +105,7 @@ export const regexpGlobal = <R>(ctx: Interpreter<R>) => {
    ],
  ])

-  const self = (thisValue: unknown, name: string) => receiver(RegExpObj, thisValue, `RegExp.prototype.${name}`)
+  const self = (thisValue: Value, name: string) => receiver(RegExpObj, thisValue, `RegExp.prototype.${name}`)
  defineAccessor(proto, "source", (thisValue) => self(thisValue, "source").regex.source)
  defineAccessor(proto, "flags", (thisValue) => self(thisValue, "flags").regex.flags)
  // The host regex holds the only lastIndex, so exec/test and the String methods share one counter.
@@ -1,16 +1,26 @@
 import { Effect } from "effect"
-import { constructor, fn, type Method, methods } from "../interpreter/native.js"
+import { constructor, fn, type Impl, type Method, methods } from "../interpreter/native.js"
 import { checkArrayLength, checkStringLength } from "../interpreter/limits.js"
 import { invalidData, IteratorSymbol, rangeError, typeError } from "../interpreter/model.js"
-import { define, hidden, Arr, IteratorObj, PromiseObj, RegExpObj, record } from "../interpreter/objects.js"
+import {
+  define,
+  hidden,
+  Arr,
+  IteratorObj,
+  RegExpObj,
+  record,
+  coerceToNumber,
+  coerceToString,
+  type Value,
+} from "../interpreter/objects.js"
 import { containsOpaqueReference, typeofValue } from "../interpreter/references.js"
 import { applyCollectionCallback, isSupportedCallback } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
 import { matchToValue, toHostRegex } from "./regexp.js"
-import { coerceToNumber, coerceToString, coercion } from "./value.js"
+import { coercion } from "./value.js"

 // console is intercepted by the interpreter before reaching here.
-const requireDataArgument = (name: string, index: number, arg: unknown): unknown => {
+const requireDataArgument = (name: string, index: number, arg: Value): Value => {
  if (containsOpaqueReference(arg)) {
    throw invalidData(`String.${name} expects argument ${index + 1} to be a data value.`)
  }
@@ -29,21 +39,23 @@ const replaceWithCallback = <R>(
  ctx: Interpreter<R>,
  value: string,
  name: "replace" | "replaceAll",
-  args: Array<unknown>,
-): Effect.Effect<unknown, unknown, R> => {
+  args: Array<Value>,
+): Effect.Effect<Value, unknown, R> => {
  const builtins = ctx.builtins
  const apply = applyCollectionCallback(ctx, args[1], `String.${name}`)
-  const matches: Array<{ readonly match: string; readonly offset: number; readonly args: Array<unknown> }> = []
-  const collect = (...callbackArgs: Array<unknown>): string => {
+  const matches: Array<{ readonly match: string; readonly offset: number; readonly args: Array<Value> }> = []
+  // The host calls back with (match, ...captures, offset, string, groups?); only groups is not already a Value.
+  const collect = (
+    ...callbackArgs: Array<string | number | undefined | Record<string, string | undefined>>
+  ): string => {
    const match = callbackArgs[0]
-    const groups = callbackArgs[callbackArgs.length - 1]
-    const hasGroups = groups !== null && typeof groups === "object"
+    const hasGroups = typeof callbackArgs.at(-1) === "object"
    const offset = callbackArgs[callbackArgs.length - (hasGroups ? 3 : 2)]
    if (typeof match !== "string" || typeof offset !== "number") {
      throw typeError(`String.${name} produced an invalid replacement match.`)
    }
-    if (hasGroups) callbackArgs[callbackArgs.length - 1] = record(builtins.Object, groups as Record<string, unknown>)
-    matches.push({ match, offset, args: callbackArgs })
+    const args = callbackArgs.map((arg) => (typeof arg === "object" ? record(builtins.Object, arg) : arg))
+    matches.push({ match, offset, args })
    return match
  }

@@ -63,10 +75,7 @@ const replaceWithCallback = <R>(
    let end = 0
    for (const match of matches) {
      const replacement = yield* apply(match.args)
-      output.push(
-        value.slice(end, match.offset),
-        replacement instanceof PromiseObj ? "[object Promise]" : coerceToString(replacement),
-      )
+      output.push(value.slice(end, match.offset), coerceToString(replacement))
      end = match.offset + match.match.length
    }
    output.push(value.slice(end))
@@ -99,7 +108,7 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
    codeUnits("fromCodePoint", String.fromCodePoint),
  ])

-  const self = (thisValue: unknown, name: string): string => {
+  const self = (thisValue: Value, name: string): string => {
    if (typeof thisValue === "string") return thisValue
    if (thisValue === null || thisValue === undefined) {
      throw typeError(`String.prototype.${name} called on null or undefined.`)
@@ -107,26 +116,26 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
    return coerceToString(thisValue)
  }
  // Coerce arguments like native JS; opaque runtime references still reject.
-  const str = (name: string, args: Array<unknown>, index: number): string =>
+  const str = (name: string, args: Array<Value>, index: number): string =>
    coerceToString(requireDataArgument(name, index, args[index]))
-  const num = (name: string, args: Array<unknown>, index: number): number =>
+  const num = (name: string, args: Array<Value>, index: number): number =>
    coerceToNumber(requireDataArgument(name, index, args[index]))
-  const optNum = (name: string, args: Array<unknown>, index: number): number | undefined =>
+  const optNum = (name: string, args: Array<Value>, index: number): number | undefined =>
    args[index] === undefined ? undefined : num(name, args, index)
-  const optStr = (name: string, args: Array<unknown>, index: number): string | undefined =>
+  const optStr = (name: string, args: Array<Value>, index: number): string | undefined =>
    args[index] === undefined ? undefined : str(name, args, index)
-  const rejectRegex = (name: string, args: Array<unknown>): void => {
+  const rejectRegex = (name: string, args: Array<Value>): void => {
    if (args[0] instanceof RegExpObj) {
      throw typeError(
        `String.${name} cannot take a regular expression; use regex.test(string) or String.search instead.`,
      )
    }
  }
-  const simple = (name: string, length: number, op: (value: string, args: Array<unknown>) => unknown): Method => [
-    name,
-    length,
-    (thisValue, args) => op(self(thisValue, name), args),
-  ]
+  const simple = (
+    name: string,
+    length: number,
+    op: (value: string, args: Array<Value>) => ReturnType<Impl>,
+  ): Method => [name, length, (thisValue, args) => op(self(thisValue, name), args)]
  const replace = (name: "replace" | "replaceAll") =>
    simple(name, 2, (value, args) => {
      if (isSupportedCallback(args[1])) return replaceWithCallback(ctx, value, name, args)
@@ -150,6 +159,8 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
    simple("valueOf", 0, (value) => value),
    simple("toLowerCase", 0, (value) => value.toLowerCase()),
    simple("toUpperCase", 0, (value) => value.toUpperCase()),
+    simple("toLocaleLowerCase", 0, (value) => value.toLowerCase()),
+    simple("toLocaleUpperCase", 0, (value) => value.toUpperCase()),
    simple("trim", 0, (value) => value.trim()),
    simple("trimStart", 0, (value) => value.trimStart()),
    simple("trimLeft", 0, (value) => value.trimStart()),
@@ -216,7 +227,7 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
          `String.matchAll requires a regular expression with the global (g) flag: write /${pattern.source}/${pattern.flags}g, or use String.match for a single match.`,
        )
      }
-      const matches: Array<unknown> = []
+      const matches: Array<Value> = []
      for (const match of value.matchAll(pattern)) {
        checkArrayLength(matches.length + 1)
        matches.push(matchToValue(builtins, match))
@@ -7,17 +7,17 @@ import {
  entries,
  get,
  hidden,
-  isWrapper,
  Arr,
  IteratorObj,
  Obj,
  URLObj,
  URLSearchParamsObj,
+  coerceToString,
+  isRuntimeReference,
+  type Value,
 } from "../interpreter/objects.js"
-import { isRuntimeReference } from "../interpreter/references.js"
 import { applyCollectionCallback, preserveConsumerError } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToString } from "./value.js"

 const urlProperties = [
  "href",
@@ -52,12 +52,12 @@ export const uriGlobal = <R>(ctx: Interpreter<R>, name: UriFunction) =>
    }
  })

-const urlArgument = (value: unknown): string => (value instanceof URLObj ? value.url.href : coerceToString(value))
+const urlArgument = (value: Value): string => (value instanceof URLObj ? value.url.href : coerceToString(value))

 export const urlGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
  const proto = builtins.URL
-  const construct = (args: Array<unknown>, into: Obj): URLObj => {
+  const construct = (args: Array<Value>, into: Obj): URLObj => {
    if (args.length === 0) {
      throw typeError("new URL(...) requires a URL string and an optional base URL.")
    }
@@ -92,7 +92,7 @@ export const urlGlobal = <R>(ctx: Interpreter<R>) => {
  ]
  methods(builtins, url, [parse("canParse"), parse("parse")])

-  const self = (thisValue: unknown, name: string) => receiver(URLObj, thisValue, `URL.prototype.${name}`)
+  const self = (thisValue: Value, name: string) => receiver(URLObj, thisValue, `URL.prototype.${name}`)
  for (const name of urlProperties) {
    defineAccessor(
      proto,
@@ -119,7 +119,7 @@ export const urlGlobal = <R>(ctx: Interpreter<R>) => {
  return url
 }

-const readPair = <R>(ctx: Interpreter<R>, value: unknown, label: string): Effect.Effect<Array<string>, unknown, R> =>
+const readPair = <R>(ctx: Interpreter<R>, value: Value, label: string): Effect.Effect<Array<string>, unknown, R> =>
  Effect.gen(function* () {
    const cursor = yield* ctx.iterate(value)
    if (cursor === undefined) throw typeError(`${label} expects iterable [name, value] pairs.`)
@@ -142,7 +142,7 @@ const readPair = <R>(ctx: Interpreter<R>, value: unknown, label: string): Effect
 */
 export const readPairs = <R>(
  ctx: Interpreter<R>,
-  init: unknown,
+  init: Value,
  label: string,
 ): Effect.Effect<Array<[string, string]> | undefined, unknown, R> =>
  Effect.gen(function* () {
@@ -161,7 +161,7 @@ export const readPairs = <R>(

 const constructURLSearchParams = <R>(
  ctx: Interpreter<R>,
-  init: unknown,
+  init: Value,
  proto: Obj,
 ): Effect.Effect<URLSearchParamsObj, unknown, R> => {
  const wrap = (params: URLSearchParams) => new URLSearchParamsObj(proto, params)
@@ -177,7 +177,6 @@ const constructURLSearchParams = <R>(
    if (isRuntimeReference(init)) {
      throw typeError("new URLSearchParams(...) expects a query string, data object, or synchronous iterable pairs.")
    }
-    if (isWrapper(init)) return wrap(new URLSearchParams())
    if (!(init instanceof Obj)) {
      throw typeError(
        "new URLSearchParams(...) expects a query string, data object, iterable pairs, or URLSearchParams.",
@@ -197,11 +196,11 @@ export const urlSearchParamsGlobal = <R>(ctx: Interpreter<R>) => {
    call: requiresNew("URLSearchParams"),
    construct: (args, newTarget) => constructURLSearchParams(ctx, args[0], prototypeFrom(newTarget, proto)),
  })
-  const self = (thisValue: unknown, name: string) =>
+  const self = (thisValue: Value, name: string) =>
    receiver(URLSearchParamsObj, thisValue, `URLSearchParams.prototype.${name}`)
-  const wrap = (items: Array<unknown>) => new Arr(builtins.Array, items)
-  const arg = (args: Array<unknown>, index: number): string => coerceToString(args[index])
-  const requireArgs = (name: string, args: Array<unknown>, count: number): void => {
+  const wrap = (items: Array<Value>) => new Arr(builtins.Array, items)
+  const arg = (args: Array<Value>, index: number): string => coerceToString(args[index])
+  const requireArgs = (name: string, args: Array<Value>, count: number): void => {
    if (args.length < count) {
      throw typeError(`URLSearchParams.${name} requires ${count} argument${count === 1 ? "" : "s"}.`)
    }
@@ -272,17 +271,7 @@ export const urlSearchParamsGlobal = <R>(ctx: Interpreter<R>) => {
    ],
    ["keys", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "keys").params.keys())],
    ["values", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "values").params.values())],
-    [
-      "entries",
-      0,
-      (thisValue) =>
-        new IteratorObj(
-          builtins.Iterator,
-          self(thisValue, "entries")
-            .params.entries()
-            .map(([key, value]) => wrap([key, value])),
-        ),
-    ],
+    ["entries", 0, (thisValue) => new IteratorObj(builtins.Iterator, self(thisValue, "entries").iterator(builtins))],
    ["toString", 0, (thisValue) => self(thisValue, "toString").params.toString()],
    [
      "forEach",
@@ -1,64 +1,13 @@
 import { fn } from "../interpreter/native.js"
 import { typeError } from "../interpreter/model.js"
-import {
-  get,
-  isWrapper,
-  type Native,
-  Arr,
-  Bytes,
-  DateObj,
-  ErrorObj,
-  MapObj,
-  RegExpObj,
-  SetObj,
-  URLObj,
-  URLSearchParamsObj,
-  HeadersObj,
-} from "../interpreter/objects.js"
+import { coerceToNumber, coerceToString, type Native, type Value } from "../interpreter/objects.js"
 import type { Interpreter } from "../interpreter/interpreter.js"

 export const compoundOperators = new Set(["+=", "-=", "*=", "/=", "%=", "**=", "&=", "|=", "^=", "<<=", ">>=", ">>>="])

-/** The built-in string form of a value, without consulting program-defined `toString` methods. */
-export const coerceToString = (value: unknown): string => {
-  if (value === null) return "null"
-  if (value === undefined) return "undefined"
-  if (value instanceof DateObj) return Number.isFinite(value.time) ? new Date(value.time).toISOString() : "Invalid Date"
-  if (value instanceof RegExpObj) return `/${value.regex.source}/${value.regex.flags}`
-  if (value instanceof MapObj) return "[object Map]"
-  if (value instanceof SetObj) return "[object Set]"
-  if (value instanceof URLObj) return value.url.href
-  if (value instanceof URLSearchParamsObj) return value.params.toString()
-  if (value instanceof HeadersObj) return "[object Headers]"
-  if (value instanceof Bytes) return value.bytes.join(",")
-  if (value instanceof ErrorObj) {
-    // Match Error.prototype.toString: "name: message", or just one when the other is empty.
-    const name = get(value, "name")
-    const message = get(value, "message")
-    const shownName = typeof name === "string" ? name : "Error"
-    const shownMessage = typeof message === "string" ? message : ""
-    if (shownMessage === "") return shownName
-    if (shownName === "") return shownMessage
-    return `${shownName}: ${shownMessage}`
-  }
-  if (value instanceof Arr) {
-    return value.items.map((item) => (item === null || item === undefined ? "" : coerceToString(item))).join(",")
-  }
-  if (typeof value === "object") return "[object Object]"
-  return String(value)
-}
-
-export const coerceToNumber = (value: unknown): number => {
-  if (value instanceof DateObj) return value.time
-  if (value instanceof Bytes) return Number(coerceToString(value))
-  if (isWrapper(value)) return Number.NaN
-  if (value instanceof Arr) return Number(coerceToString(value))
-  return value !== null && typeof value === "object" ? Number.NaN : Number(value)
-}
-
 export type Coercion = "Number" | "String" | "Boolean" | "parseInt" | "parseFloat" | "isFinite" | "isNaN"

-const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<unknown>): unknown => {
+const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<Value>): Value => {
  // Native: Number() is 0 and String() is "", unlike their undefined-argument forms; the
  // other coercers match native through the undefined-argument path below.
  if (args.length === 0) {
@@ -66,15 +15,6 @@ const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<unknown>): u
    if (name === "String") return ""
  }
  const raw = args[0]
-  if (isWrapper(raw)) {
-    if (name === "Boolean") return true
-    if (name === "Number") return coerceToNumber(raw)
-    if (name === "String") return coerceToString(raw)
-    if (name === "isFinite") return Number.isFinite(coerceToNumber(raw))
-    if (name === "isNaN") return Number.isNaN(coerceToNumber(raw))
-    if (name === "parseInt") return parseInt(coerceToString(raw))
-    return parseFloat(coerceToString(raw))
-  }
  if (name === "Number") return coerceToNumber(raw)
  if (name === "Boolean") return Boolean(raw)
  if (name === "isFinite") return Number.isFinite(coerceToNumber(raw))
@@ -1,9 +1,8 @@
 import { fn, methods } from "../interpreter/native.js"
 import { typeError } from "../interpreter/model.js"
-import { Bytes, Obj } from "../interpreter/objects.js"
+import { Bytes, Obj, coerceToString } from "../interpreter/objects.js"
 import { describeValue } from "../interpreter/references.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coerceToString } from "./value.js"

 // WebIDL DOMString conversion: a missing argument is a TypeError, anything else stringifies. Invalid input is a
 // TypeError as well; browsers throw a DOMException named InvalidCharacterError, which CodeMode does not have.
@@ -22,6 +22,16 @@ describe("source syntax", () => {
 })

 describe("error identity", () => {
+  test("Error.isError is true for every Error value and nothing else", async () => {
+    expect(
+      await value(`
+        const caught = (() => { try { null.foo } catch (error) { return error } })()
+        return [Error.isError(new Error("x")), Error.isError(new RangeError("x")), Error.isError(caught),
+          Error.isError({ name: "Error", message: "x" }), Error.isError("Error"), Error.isError(null)]
+      `),
+    ).toEqual([true, true, true, false, false, false])
+  })
+
  test("awaiting the same rejected promise twice yields the same error object", async () => {
    expect(
      await value(`
@@ -529,6 +529,6 @@ describe("Test262 for-await-of adaptations", () => {
    const result = await execute(`for await (const item of { values: [1, 2] }) {}`)
    expect(result.ok).toBe(false)
    if (result.ok) return
-    expect(result.error.message).toContain("or custom iterator value")
+    expect(result.error.message).toContain("requires an iterable value, received a data object")
  })
 })
@@ -1030,7 +1030,7 @@ describe("confined generators", () => {
        const params = new URLSearchParams(entries())
        return [events, params.toString()]
      `),
-    ).toEqual([["first", "second", "pair close", "outer close"], "%5Bobject+Object%5D=2"])
+    ).toEqual([["first", "second", "pair close", "outer close"], "%5Bobject+Promise%5D=2"])
  })

  test("validates URLSearchParams pair lengths after converting the outer sequence", async () => {
@@ -898,6 +898,42 @@ describe("Map", () => {
    ).toEqual({ a: 3, b: 1, c: 1 })
  })

+  test("getOrInsert and getOrInsertComputed insert only when the key is missing", async () => {
+    expect(
+      await value(`
+      const groups = new Map()
+      groups.getOrInsert("a", []).push(1)
+      groups.getOrInsert("a", []).push(2)
+      let calls = 0
+      const computed = (key) => { calls++; return key + "!" }
+      const first = groups.getOrInsertComputed("b", computed)
+      const second = groups.getOrInsertComputed("b", computed)
+      const zero = groups.getOrInsertComputed(-0, (key) => 1 / key === Infinity)
+      return [[...groups], first, second, calls, zero]
+    `),
+    ).toEqual([
+      [
+        ["a", [1, 2]],
+        ["b", "b!"],
+        [0, true],
+      ],
+      "b!",
+      "b!",
+      1,
+      true,
+    ])
+    expect(
+      await value(`
+      const m = new Map()
+      const outer = m.getOrInsertComputed("k", () => { m.set("k", "inner"); return "outer" })
+      let thrown
+      try { m.getOrInsertComputed("j", () => { throw new Error("boom") }) } catch (error) { thrown = error.message }
+      return [outer, m.get("k"), thrown, m.has("j")]
+    `),
+    ).toEqual(["outer", "outer", "boom", false])
+    expect((await error(`new Map().getOrInsertComputed("k", 5)`)).message).toContain("expects a function callback")
+  })
+
  test("maps serialize to {} at the boundary, like JSON", async () => {
    expect(await value(`return new Map([["a", 1]])`)).toEqual({})
    expect(await value(`return JSON.stringify(new Map([["a", 1]]))`)).toBe("{}")
@@ -1061,7 +1097,7 @@ describe("Uint8Array", () => {
      console.log(b, new Uint8Array())
      return [String(b), b + "", +new Uint8Array([5]), Number.isNaN(Number(b)), b == "1,2", JSON.stringify(b), b.toLocaleString(), typeof b, b instanceof Uint8Array]
    `),
-    ).toEqual(["1,2", "1,2", 5, true, true, '{"0":1,"1":2}', "[object Uint8Array]", "object", true])
+    ).toEqual(["1,2", "1,2", 5, true, true, '{"0":1,"1":2}', "1,2", "object", true])
    expect((await run(`console.log(new Uint8Array([1, 2]), new Uint8Array())`)).logs).toEqual([
      "Uint8Array(2) [1,2] Uint8Array(0) []",
    ])
@@ -1231,6 +1267,75 @@ describe("built-in iterators", () => {
  })
 })

+describe("Object.prototype.toString", () => {
+  test("reports the built-in kind it is inherited by, as JS does through Symbol.toStringTag", async () => {
+    expect(
+      await value(`
+      return [
+        new Map().toString(), new Set().toString(), new Headers().toString(), Promise.resolve(1).toString(),
+        [1].values().toString(), ({}).toString(), String(new Map()), String(Promise.resolve(1)),
+        \`\${new Set([1])}\`, [new Map()] + "", new Map() == "[object Map]",
+      ]
+    `),
+    ).toEqual([
+      "[object Map]",
+      "[object Set]",
+      "[object Headers]",
+      "[object Promise]",
+      "[object Iterator]",
+      "[object Object]",
+      "[object Map]",
+      "[object Promise]",
+      "[object Set]",
+      "[object Map]",
+      true,
+    ])
+  })
+})
+
+describe("toLocaleString", () => {
+  test("numbers and dates format as en-US in UTC; everything else falls back to toString", async () => {
+    expect(
+      await value(`
+      return [
+        (1234567.891).toLocaleString(), new Date(0).toLocaleString(), new Date(0).toLocaleDateString(),
+        new Date(0).toLocaleTimeString(), "a".toLocaleString(), true.toLocaleString(), ({}).toLocaleString(),
+        ({ toString: () => "custom" }).toLocaleString(), new Uint8Array([1, 2]).toLocaleString(),
+      ]
+    `),
+    ).toEqual([
+      "1,234,567.891",
+      "1/1/1970, 12:00:00 AM",
+      "1/1/1970",
+      "12:00:00 AM",
+      "a",
+      "true",
+      "[object Object]",
+      "custom",
+      "1,2",
+    ])
+  })
+
+  test("arrays join each element's toLocaleString, skipping holes and nullish elements", async () => {
+    expect(
+      await value(`
+      let calls = 0
+      const item = { toLocaleString() { calls++; return "o" } }
+      return [[1234.5, "x", null, undefined, item, new Date(0)].toLocaleString(), [, item, , item].toLocaleString(), calls]
+    `),
+    ).toEqual(["1,234.5,x,,,o,1/1/1970, 12:00:00 AM", ",o,,o", 3])
+    expect((await error(`const f = ({}).toLocaleString; f()`)).message).toContain(
+      "Object.prototype.toLocaleString called on null or undefined",
+    )
+  })
+
+  test("toLocaleLowerCase and toLocaleUpperCase ignore the locale argument", async () => {
+    expect(
+      await value(`return ["ABC".toLocaleLowerCase("tr"), "abc".toLocaleUpperCase(), "İ".toLocaleLowerCase()]`),
+    ).toEqual(["abc", "ABC", "i̇"])
+  })
+})
+
 describe("stdlib integration", () => {
  test("constructor follows own keys, shadowing, writes, and new", async () => {
    expect(
@@ -9,7 +9,7 @@ import type { Interpreter } from "../../src/interpreter/interpreter.js"
 import { Throw } from "../../src/interpreter/model.js"
 import { createErrorValue } from "../../src/interpreter/intrinsics.js"
 import { constructor, fn, methods } from "../../src/interpreter/native.js"
-import { Callable, define, get, hidden, Arr, Fn, Obj } from "../../src/interpreter/objects.js"
+import { Callable, define, get, hidden, Arr, Fn, Obj, type Value } from "../../src/interpreter/objects.js"
 import { ToolRuntime } from "../../src/tool-runtime.js"

 export const root = import.meta.dir
@@ -64,10 +64,7 @@ export const run = async (file: string): Promise<Outcome> => {
  return { status: "pass" }
 }

-const harness = <R>(
-  ctx: Interpreter<R>,
-  onDone: (error: unknown) => void,
-): ReadonlyArray<readonly [string, unknown]> => {
+const harness = <R>(ctx: Interpreter<R>, onDone: (error: Value) => void): ReadonlyArray<readonly [string, Value]> => {
  const builtins = ctx.builtins
  const test262Prototype = new Obj(builtins.Object)
  define(test262Prototype, "name", "Test262Error", hidden)
@@ -90,7 +87,7 @@ const harness = <R>(
  methods(builtins, compareArray, [["format", 1, (_, args) => show(args[0])]])
  const assert = fn<R>(builtins, "assert", 2, (_, args) =>
    args[0] === true
-      ? Effect.void
+      ? Effect.undefined
      : fail(args[1] === undefined ? `Expected true but got ${show(args[0])}` : String(args[1])),
  )
  methods(builtins, assert, [
@@ -99,7 +96,7 @@ const harness = <R>(
      3,
      (_, args) =>
        Object.is(args[0], args[1])
-          ? Effect.void
+          ? Effect.undefined
          : fail(`${prefix(args[2])}Expected SameValue(«${show(args[0])}», «${show(args[1])}») to be true`),
    ],
    [
@@ -108,14 +105,14 @@ const harness = <R>(
      (_, args) =>
        Object.is(args[0], args[1])
          ? fail(`${prefix(args[2])}Expected SameValue(«${show(args[0])}», «${show(args[1])}») to be false`)
-          : Effect.void,
+          : Effect.undefined,
    ],
    [
      "compareArray",
      3,
      (_, args) =>
        compare(args[0], args[1])
-          ? Effect.void
+          ? Effect.undefined
          : fail(
              `Actual ${show(args[0])} and expected ${show(args[1])} should have the same contents. ${prefix(args[2])}`,
            ),
@@ -132,7 +129,7 @@ const harness = <R>(
              const thrown = materialize(ctx, Cause.squash(cause))
              if (!(thrown instanceof Obj)) return fail(`${prefix(args[2])}Thrown value was not an object!`)
              const actual = get(thrown, "constructor")
-              if (actual === args[0]) return Effect.void
+              if (actual === args[0]) return Effect.undefined
              return fail(`${prefix(args[2])}Expected a ${expected} but got a ${show(actual)}`)
            },
            onSuccess: () =>
@@ -146,7 +143,13 @@ const harness = <R>(
    ["assert", assert],
    ["compareArray", compareArray],
    ["Test262Error", test262Error],
-    ["$DONE", fn<R>(builtins, "$DONE", 1, (_, args) => onDone(args[0]))],
+    [
+      "$DONE",
+      fn<R>(builtins, "$DONE", 1, (_, args) => {
+        onDone(args[0])
+        return undefined
+      }),
+    ],
    [
      "$DONOTEVALUATE",
      fn<R>(builtins, "$DONOTEVALUATE", 0, () =>
@@ -225,7 +225,6 @@ built-ins/Array/prototype/splice/S15.4.4.12_A4_T1.js  # Array.prototype.splice c
 built-ins/Array/prototype/splice/S15.4.4.12_A4_T2.js  # Array.prototype.splice called on incompatible receiver a data object.
 built-ins/Array/prototype/splice/S15.4.4.12_A4_T3.js  # Array.prototype.splice called on incompatible receiver a data object.
 built-ins/Array/prototype/splice/create-ctor-non-object.js  # null value Expected a TypeError to be thrown but no exception was thrown at all
-built-ins/Array/prototype/toLocaleString/S15.4.4.3_A1_T1.js  # #1: var n = 0; var obj = {toLocaleString: function() {n++}}; var arr = [undefined, obj, null, obj, o
 built-ins/Array/prototype/toLocaleString/S15.4.4.3_A3_T1.js  # #1: var n = 0; var obj = {toLocaleString: function() {n++}}; Array.prototype[1] = obj; x = [obj]; x.
 built-ins/Array/prototype/toReversed/holes-not-preserved.js  # Actual [4, undefined, 2, undefined, 0] and expected [4, 3, 2, undefined, 0] should have the same con
 built-ins/Array/prototype/toSorted/holes-not-preserved.js  # Actual [1, 3, 4, undefined, undefined] and expected [1, 2, 3, 4, undefined] should have the same con
@@ -1,6 +1,6 @@
 {
  "name": "@opencode/console-app",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "type": "module",
  "license": "MIT",
  "scripts": {
@@ -1,7 +1,7 @@
 {
  "$schema": "https://json.schemastore.org/package.json",
  "name": "@opencode/console-core",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "private": true,
  "type": "module",
  "license": "MIT",
@@ -1,6 +1,6 @@
 {
  "name": "@opencode/console-function",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "$schema": "https://json.schemastore.org/package.json",
  "private": true,
  "type": "module",
@@ -1,6 +1,6 @@
 {
  "name": "@opencode/console-mail",
-  "version": "2.0.10",
+  "version": "2.0.11",
  "dependencies": {
    "@jsx-email/all": "2.2.3",
    "@jsx-email/cli": "1.4.3",
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Aiden Cline	a72262cffc	refactor(codemode): type program values as Value	2026-09-20 11:03:16 -05:00
Aiden Cline	003bf86df9	refactor(codemode): let each built-in object answer for itself	2026-09-20 10:45:53 -05:00
Aiden Cline	62dc1f7696	feat(codemode): add toLocaleString, Error.isError, and Map.getOrInsert (#50098 )	2026-09-20 10:23:23 -05:00
opencode-agent[bot]	66f10ab7bf	chore(core): refresh bundled models.dev snapshot	2026-09-20 14:37:06 +00:00
opencode-agent[bot]	1ca8f63a79	chore(core): refresh bundled models.dev snapshot	2026-09-20 13:36:51 +00:00
opencode-agent[bot]	03bcdd580d	chore(core): refresh bundled models.dev snapshot	2026-09-20 12:43:39 +00:00
opencode-agent[bot]	cc502f7e5f	chore(core): refresh bundled models.dev snapshot	2026-09-20 11:37:37 +00:00
opencode-agent[bot]	64ce8771c0	chore(core): refresh bundled models.dev snapshot	2026-09-20 10:37:01 +00:00
opencode-agent[bot]	702a73d91a	chore(core): refresh bundled models.dev snapshot	2026-09-20 09:37:50 +00:00
opencode	991b727eb8	sync release versions for v2.0.11	2026-09-20 08:57:41 +00:00
opencode-agent[bot]	ba342ce227	chore(core): refresh bundled models.dev snapshot	2026-09-20 08:42:13 +00:00
David Hill	1464545665	fix(app): center timeline beside summary (#49620 )	2026-09-20 18:06:32 +10:00
David Hill	fecacc9e68	fix(app): match vertical nav tab states (#49619 )	2026-09-20 18:03:49 +10:00
David HillandLukeParkerDev	1f73b4806b	fix(desktop): polish browser panel states and navigation (#49432 ) Co-authored-by: LukeParkerDev <10430890+Hona@users.noreply.github.com>	2026-09-20 07:54:25 +00:00
opencode-agent[bot]	da2ce02596	chore(core): refresh bundled models.dev snapshot	2026-09-20 07:38:48 +00:00
opencode-agent[bot]	25f35dcfb8	chore(core): refresh bundled models.dev snapshot	2026-09-20 06:49:40 +00:00