fix(tui): warn when launch directory falls back

feat(codemode): add WeakMap and WeakSet (#51257 )
Revert "fix(core): fit model limits and recover compaction overflow" (#51273 )
2026-09-26 02:27:36 +00:00 · 2026-09-25 05:27:22 +00:00 · 2026-09-25 00:15:19 -05:00 · 2026-09-25 00:12:14 -05:00 · 2026-09-25 00:11:40 -05:00 · 2026-09-25 05:03:33 +00:00
47 changed files with 2501 additions and 591 deletions
@@ -2,7 +2,7 @@ import { DialogProvider } from "@opencode/ui/context/dialog"
 import { Browser } from "@opencode/plugin-browser/rpc"
 import { For, Show } from "solid-js"
 import { createStore } from "solid-js/store"
-import { render } from "solid-js/web"
+import { Portal, render } from "solid-js/web"
 import { LanguageProvider, UiI18nBridge } from "../src/runtime/i18n/language"
 import type { BrowserPaneLayout, BrowserPaneRegistration } from "../src/runtime/platform/browser-pane"
 import type { createSessionBrowser } from "../src/session/browser/model"
@@ -27,7 +27,12 @@ export function mountBrowserPane() {
      loadErrors: {} as Record<string, string | undefined>,
      error: undefined as string | undefined,
      layouts: {} as Record<string, BrowserPaneLayout | undefined>,
+      covered: false,
+      captures: 0,
+      holdCapture: false,
    })
+    // Each capture waits until the fixture releases it, so a spec can observe the pending state.
+    const held: (() => void)[] = []
    const tabs = ["Alpha", "Beta"].map((name) => ({
      id: Browser.TabID.make(`tab_${name === "Alpha" ? "11111111" : "22222222"}-1111-1111-1111-111111111111`),
      title: name,
@@ -44,6 +49,17 @@ export function mountBrowserPane() {
        {
          setLayout: (layout) => setStore("layouts", tab.title, layout),
          command: async () => undefined,
+          capture: async () => {
+            setStore("captures", (count) => count + 1)
+            if (store.holdCapture) await new Promise<void>((resolve) => held.push(resolve))
+            const canvas = new OffscreenCanvas(4, 4)
+            const paint = canvas.getContext("2d")
+            if (paint) {
+              paint.fillStyle = "#3b82f6"
+              paint.fillRect(0, 0, 4, 4)
+            }
+            return canvas.convertToBlob()
+          },
          close: () => undefined,
        },
      ]),
@@ -118,12 +134,34 @@ export function mountBrowserPane() {
            Complete navigation
          </button>
          <button onClick={() => setStore("visible", (visible) => !visible)}>Toggle Review tab</button>
+          <button onClick={() => setStore("holdCapture", true)}>Hold capture</button>
+          <button onClick={() => held.splice(0).forEach((resolve) => resolve())}>Release capture</button>
+          <button onClick={() => setStore("covered", (covered) => !covered)}>Toggle popover</button>
        </nav>
-        <div style={{ width: "640px", height: "360px", border: "1px solid #555" }}>
+        <p>Captures: {store.captures}</p>
+        <div style={{ position: "relative", width: "640px", height: "360px", border: "1px solid #555" }}>
          <Show when={store.mounted}>
            <SessionBrowserPane browser={browser} visible={store.visible} />
          </Show>
        </div>
+        <Show when={store.covered}>
+          {/* Floating content portals into <body> like a menu or hover card over the page. */}
+          <Portal mount={document.body}>
+            <div
+              data-popper-positioner
+              data-testid="fixture-popover"
+              style={{
+                position: "fixed",
+                top: "0",
+                left: "0",
+                width: "320px",
+                height: "480px",
+                "z-index": "1001",
+                "pointer-events": "none",
+              }}
+            />
+          </Portal>
+        </Show>
        <h2 style={{ "font-size": "18px", margin: "20px 0 12px" }}>Native layout recorder</h2>
        <p>The desktop boundary keeps each session's page visible until its registration is hidden.</p>
        <For each={tabs}>
@@ -58,6 +58,27 @@ story("hides the native view immediately while the pane stays mounted", async ({
  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
 })

+story("keeps a still of the page under floating content that covers it", async ({ page }, testInfo) => {
+  const root = page.getByTestId("browser-pane-fixture")
+  const still = root.locator("#browser-panel img")
+  await root.getByRole("button", { name: "Hold capture", exact: true }).click()
+  await root.getByRole("button", { name: "Toggle popover", exact: true }).click()
+  await expect(root.getByText("Captures: 1", { exact: true })).toBeVisible()
+  // The native page stays up until its still is ready, so the pane never shows blank.
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(still).toHaveCount(0)
+
+  await root.getByRole("button", { name: "Release capture", exact: true }).click()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "false")
+  await expect(still).toBeVisible()
+  await page.screenshot({ path: testInfo.outputPath("covered.png") })
+
+  await root.getByRole("button", { name: "Toggle popover", exact: true }).click()
+  await expect(root.getByTestId("native-Alpha")).toHaveAttribute("data-visible", "true")
+  await expect(still).toHaveCount(0)
+  await expect(root.getByText("Captures: 1", { exact: true })).toBeVisible()
+})
+
 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()
@@ -1439,6 +1439,15 @@ export const dict = {
  "settings.providers.section.connected": "Connected providers",
  "settings.providers.connected.empty": "No connected providers",
  "settings.providers.connected.environmentDescription": "Connected from your environment variables",
+  "settings.providers.account.manage": "Manage {{provider}} accounts",
+  "settings.providers.account.group": "Accounts",
+  "settings.providers.account.add": "Add account",
+  "settings.providers.account.remove": "Remove account…",
+  "settings.providers.account.active": "Active",
+  "settings.providers.account.switched.title": "{{provider}} account switched",
+  "settings.providers.account.switched.description": "Now using {{account}}.",
+  "settings.providers.account.removed.title": "{{account}} removed",
+  "settings.providers.account.removed.description": "{{provider}} will no longer use this account.",
  "settings.providers.console.available.one": "{{count}} provider available",
  "settings.providers.console.available.other": "{{count}} providers available",
  "settings.providers.section.popular": "Popular providers",
@@ -25,6 +25,8 @@ export type BrowserPaneEvent =
 export type BrowserPaneRegistration = {
  setLayout(layout?: BrowserPaneLayout): void
  command(command: BrowserPaneCommand): Promise<void>
+  /** Captures the shown page, or resolves null when nothing is on screen. */
+  capture(tabID: Browser.TabID): Promise<Blob | null>
  close(): void
 }

@@ -43,6 +43,9 @@ function fixture() {
          async command(command) {
            call.commands.push(command)
          },
+          async capture() {
+            return null
+          },
          close() {
            call.closed = true
          },
@@ -11,6 +11,7 @@ import { createStore } from "solid-js/store"
 import { useLanguage } from "@/runtime/i18n/language"
 import { usePlatform } from "@/runtime/platform/platform"
 import { useCommand } from "@/shell/commands/command"
+import type { Browser } from "@opencode/plugin-browser/rpc"
 import type { createSessionBrowser } from "./model"

 export function SessionBrowserPane(props: { browser: ReturnType<typeof createSessionBrowser>; visible: boolean }) {
@@ -30,6 +31,8 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
    // A submitted navigation the browser has not reported yet; keeps the empty state hidden meanwhile.
    navigating: false,
    visible: typeof document === "undefined" || document.visibilityState === "visible",
+    // A still of the page shown in the DOM while floating content covers the hidden native view.
+    snapshot: undefined as { tabID: Browser.TabID; url: string } | undefined,
  })
  const empty = () => !address() && !state()?.loading && !store.navigating
  let surface: HTMLDivElement | undefined
@@ -37,6 +40,8 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
  let frame: number | undefined
  let layout: string | undefined
  let until = 0
+  let capturing: Browser.TabID | undefined
+  let release: ReturnType<typeof setTimeout> | undefined
  const canvas = document.createElement("canvas")
  canvas.width = canvas.height = 1
  const paint = canvas.getContext("2d", { willReadFrequently: true })
@@ -69,6 +74,45 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
      const r = el.getBoundingClientRect()
      return r.width > 0 && r.left < rect.right && r.right > rect.left && r.top < rect.bottom && r.bottom > rect.top
    })
+  const replaceSnapshot = (next?: { tabID: Browser.TabID; url: string }) => {
+    if (store.snapshot?.url) URL.revokeObjectURL(store.snapshot.url)
+    setStore("snapshot", next)
+  }
+  // Keep the page on screen as a still under the floating content. The native view
+  // stays visible until the still has decoded, so the pane never flashes blank.
+  const freeze = (tabID: Browser.TabID) => {
+    clearTimeout(release)
+    release = undefined
+    if (store.snapshot?.tabID === tabID || capturing === tabID) return
+    capturing = tabID
+    void (registration()?.capture(tabID) ?? Promise.resolve(null))
+      .catch(() => null)
+      .then(async (blob) => {
+        const url = blob ? URL.createObjectURL(blob) : ""
+        if (url) {
+          const image = new Image()
+          image.src = url
+          await image.decode().catch(() => undefined)
+        }
+        if (capturing !== tabID) {
+          if (url) URL.revokeObjectURL(url)
+          return
+        }
+        capturing = undefined
+        // A failed capture still hides the page; the pane shows its background as before.
+        replaceSnapshot({ tabID, url })
+        schedule()
+      })
+  }
+  const thaw = () => {
+    capturing = undefined
+    if (!store.snapshot || release !== undefined) return
+    // Keep the still under the native view until the view has painted again.
+    release = setTimeout(() => {
+      release = undefined
+      replaceSnapshot()
+    }, 150)
+  }
  const measure = () => {
    if (!surface) return
    const tab = state()
@@ -84,7 +128,11 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
    const bottom = Math.round(rect.bottom * zoom)
    // 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)
+    const shown = props.visible && store.visible && !empty() && !failed() && !dialog.active
+    const cover = covered(rect)
+    if (shown && cover) freeze(tab.id)
+    if (!cover) thaw()
+    const visible = shown && !(cover && store.snapshot?.tabID === tab.id)
    // The cutout exposes the app backdrop outside the rounded Review card,
    // not the browser surface inside it.
    const color = getComputedStyle(
@@ -186,6 +234,9 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
  createEventListener(document, "visibilitychange", () => setStore("visible", document.visibilityState === "visible"))
  onCleanup(() => {
    if (frame !== undefined) cancelAnimationFrame(frame)
+    clearTimeout(release)
+    capturing = undefined
+    replaceSnapshot()
  })

  return (
@@ -296,7 +347,17 @@ export function SessionBrowserPane(props: { browser: ReturnType<typeof createSes
          {error()}
        </div>
      </Show>
-      <div ref={surface} class="min-h-0 flex-1 bg-v2-background-bg-base flex items-center justify-center">
+      <div ref={surface} class="relative min-h-0 flex-1 bg-v2-background-bg-base flex items-center justify-center">
+        <Show when={store.snapshot?.tabID === state()?.id && !empty() && !failed() && store.snapshot?.url}>
+          {(url) => (
+            <img
+              src={url()}
+              alt=""
+              draggable={false}
+              class="absolute inset-0 size-full pointer-events-none select-none"
+            />
+          )}
+        </Show>
        <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
@@ -0,0 +1,34 @@
+import { describe, expect, test } from "bun:test"
+import type { IntegrationInfo } from "@opencode/client/promise"
+import { activeProviderAccount, providerAccounts } from "./accounts"
+
+const integration = (connections: IntegrationInfo["connections"]): IntegrationInfo => ({
+  id: "openai",
+  name: "OpenAI",
+  methods: [],
+  connections,
+})
+
+describe("provider accounts", () => {
+  test("preserves the server's active-first credential order", () => {
+    const value = integration([
+      { type: "credential", id: "cred_work", label: "Work", method: "key" },
+      { type: "env", name: "OPENAI_API_KEY" },
+      { type: "credential", id: "cred_personal", label: "Personal", method: "oauth" },
+    ])
+
+    expect(providerAccounts(value)).toEqual([
+      { type: "credential", id: "cred_work", label: "Work", method: "key" },
+      { type: "credential", id: "cred_personal", label: "Personal", method: "oauth" },
+    ])
+    expect(activeProviderAccount(value)).toEqual({ type: "credential", id: "cred_work", label: "Work", method: "key" })
+  })
+
+  test("returns no active account for environment-only integrations", () => {
+    const value = integration([{ type: "env", name: "OPENAI_API_KEY" }])
+
+    expect(providerAccounts(value)).toEqual([])
+    expect(activeProviderAccount(value)).toBeUndefined()
+    expect(providerAccounts(undefined)).toEqual([])
+  })
+})
@@ -0,0 +1,11 @@
+import type { ConnectionInfo, IntegrationInfo } from "@opencode/client/promise"
+
+export type ProviderAccount = Extract<ConnectionInfo, { type: "credential" }>
+
+export function providerAccounts(integration: IntegrationInfo | undefined) {
+  return integration?.connections.filter((connection): connection is ProviderAccount => connection.type === "credential") ?? []
+}
+
+export function activeProviderAccount(integration: IntegrationInfo | undefined) {
+  return providerAccounts(integration)[0]
+}
@@ -2,6 +2,7 @@ import { Button } from "@opencode/ui/button"
 import { Badge } from "@opencode/ui/badge"
 import { useDialog } from "@opencode/ui/context/dialog"
 import { Icon } from "@opencode/ui/icon"
+import { Menu } from "@opencode/ui/menu"
 import { OpenCodeLogo } from "@/providers/opencode-logo"
 import { showToast } from "@/shell/notifications/toast"
 import { popularProviders, useProviders } from "@/providers/catalog/providers"
@@ -16,6 +17,7 @@ import { CONSOLE_INTEGRATION, CONSOLE_PROVIDERS } from "@/providers/connect/cont
 import { DialogConnectProvider, useProviderConnectController } from "@/providers/connect/dialog"
 import { ProviderModelIcon } from "@/providers/models/provider-group"
 import { SettingsList } from "@/settings/list"
+import { activeProviderAccount, providerAccounts, type ProviderAccount } from "./accounts"
 import "@/settings/settings.css"

 type ProviderSource = "env" | "api" | "account" | "config" | "custom"
@@ -47,6 +49,7 @@ export const SettingsProviders: Component<{
    disconnecting: {} as Record<string, "removing" | "removed" | "absent" | undefined>,
    consoleExpanded: false,
    connecting: false,
+    credentialID: undefined as string | undefined,
  })
  const updateDisconnecting = (ids: string[], status: "removing" | "removed" | "absent" | undefined) =>
    setState("disconnecting", (current) => ({
@@ -190,6 +193,8 @@ export const SettingsProviders: Component<{
    return currentSource !== "env" && currentSource !== "config"
  }

+  const canManageAccounts = (item: ProviderItem) => providerAccounts(integration(item)).length > 0
+
  const note = (id: string) => PROVIDER_NOTES.find((item) => item.match(id))?.key

  const disconnect = async (item: ProviderItem, name: string) => {
@@ -230,6 +235,132 @@ export const SettingsProviders: Component<{
      })
  }

+  const refreshAccounts = async () => {
+    const location = props.directory ? { directory: props.directory } : undefined
+    data.location.integration.invalidate(location)
+    data.location.provider.invalidate(location)
+    data.location.model.invalidate(location)
+    await Promise.all([
+      data.location.integration.sync(location),
+      data.location.provider.sync(location),
+      data.location.model.sync(location),
+    ])
+  }
+
+  const accountError = (error: unknown) => {
+    const message = error instanceof Error ? error.message : String(error)
+    showToast({ title: language.t("common.requestFailed"), description: message })
+  }
+
+  const activate = async (provider: ProviderItem, providerName: string, account: ProviderAccount) => {
+    if (activeProviderAccount(integration(provider))?.id === account.id) return
+    setState("credentialID", account.id)
+    await serverSdk.api.credential
+      .activate({ credentialID: account.id })
+      .then(refreshAccounts)
+      .then(() =>
+        showToast({
+          variant: "success",
+          icon: "circle-check",
+          title: language.t("settings.providers.account.switched.title", { provider: providerName }),
+          description: language.t("settings.providers.account.switched.description", { account: account.label }),
+        }),
+      )
+      .catch(accountError)
+      .finally(() => setState("credentialID", undefined))
+  }
+
+  const remove = async (provider: ProviderItem, providerName: string, account: ProviderAccount) => {
+    const final = providerAccounts(integration(provider)).length === 1
+    setState("credentialID", account.id)
+    await serverSdk.api.credential
+      .remove({ credentialID: account.id })
+      .then(refreshAccounts)
+      .then(() =>
+        showToast({
+          variant: "success",
+          icon: "circle-check",
+          title: language.t(
+            final ? "provider.disconnect.toast.disconnected.title" : "settings.providers.account.removed.title",
+            final ? { provider: providerName } : { account: account.label },
+          ),
+          description: language.t(
+            final
+              ? "provider.disconnect.toast.disconnected.description"
+              : "settings.providers.account.removed.description",
+            { provider: providerName },
+          ),
+        }),
+      )
+      .catch(accountError)
+      .finally(() => setState("credentialID", undefined))
+  }
+
+  function AccountMenu(menuProps: { provider: ProviderItem; name?: string }) {
+    const accounts = () => providerAccounts(integration(menuProps.provider))
+    const active = () => activeProviderAccount(integration(menuProps.provider))
+    const name = () => menuProps.name ?? menuProps.provider.name
+
+    return (
+      <Menu placement="bottom-end" gutter={6}>
+        <Menu.Trigger
+          as={Button}
+          size="normal"
+          variant="ghost-muted"
+          class="settings-provider-account-trigger"
+          aria-label={language.t("settings.providers.account.manage", { provider: name() })}
+        >
+          <span>{active()?.label}</span>
+          <Icon name="chevron-down" size="small" />
+        </Menu.Trigger>
+        <Menu.Portal>
+          <Menu.Content class="settings-provider-account-menu" onEscapeKeyDown={(event) => event.stopPropagation()}>
+            <Menu.Group>
+              <Menu.GroupLabel>{language.t("settings.providers.account.group")}</Menu.GroupLabel>
+              <Menu.RadioGroup
+                class="settings-provider-account-list"
+                value={active()?.id}
+                onChange={(credentialID) => {
+                  const account = accounts().find((item) => item.id === credentialID)
+                  if (account) void activate(menuProps.provider, name(), account)
+                }}
+              >
+                <For each={accounts()}>
+                  {(account) => (
+                    <Menu.RadioItem value={account.id} closeOnSelect disabled={state.credentialID !== undefined}>
+                      <span class="settings-provider-account-label">{account.label}</span>
+                    </Menu.RadioItem>
+                  )}
+                </For>
+              </Menu.RadioGroup>
+            </Menu.Group>
+            <Menu.Separator />
+            <Menu.Item disabled={state.credentialID !== undefined} onSelect={() => connect(menuProps.provider.id)}>
+              {language.t("settings.providers.account.add")}
+            </Menu.Item>
+            <Menu.Sub placement="left-start">
+              <Menu.SubTrigger disabled={state.credentialID !== undefined || accounts().length === 0}>
+                {language.t("settings.providers.account.remove")}
+              </Menu.SubTrigger>
+              <Menu.SubContent class="settings-provider-account-submenu">
+                <For each={accounts()}>
+                  {(account) => (
+                    <Menu.Item
+                      badge={account.id === active()?.id ? language.t("settings.providers.account.active") : undefined}
+                      onSelect={() => void remove(menuProps.provider, name(), account)}
+                    >
+                      <span class="settings-provider-account-label">{account.label}</span>
+                    </Menu.Item>
+                  )}
+                </For>
+              </Menu.SubContent>
+            </Menu.Sub>
+          </Menu.Content>
+        </Menu.Portal>
+      </Menu>
+    )
+  }
+
  return (
    <>
      <div class="settings-tab-header">
@@ -268,22 +399,27 @@ export const SettingsProviders: Component<{
                            </div>
                          </div>
                          <Show
-                            when={canDisconnect(item)}
+                            when={canManageAccounts(item)}
                            fallback={
-                              <span class="settings-provider-env-hint">
-                                {language.t("settings.providers.connected.environmentDescription")}
-                              </span>
+                              <Show
+                                when={canDisconnect(item)}
+                                fallback={
+                                  <span class="settings-provider-env-hint">
+                                    {language.t("settings.providers.connected.environmentDescription")}
+                                  </span>
+                                }
+                              >
+                                <Button
+                                  size="normal"
+                                  variant="ghost-muted"
+                                  onClick={() => void disconnect(item, item.name)}
+                                >
+                                  {language.t("common.disconnect")}
+                                </Button>
+                              </Show>
                            }
                          >
-                            <Button
-                              size="normal"
-                              variant="ghost-muted"
-                              onClick={() =>
-                                void disconnect(item, item.name)
-                              }
-                            >
-                              {language.t("common.disconnect")}
-                            </Button>
+                            <AccountMenu provider={item} />
                          </Show>
                        </div>
                      }
@@ -326,13 +462,20 @@ export const SettingsProviders: Component<{
                                </Show>
                              </div>
                            </div>
-                            <Button
-                              size="normal"
-                              variant="ghost-muted"
-                              onClick={() => void disconnect(item, language.t("provider.connect.opencode.name"))}
+                            <Show
+                              when={canManageAccounts(item)}
+                              fallback={
+                                <Button
+                                  size="normal"
+                                  variant="ghost-muted"
+                                  onClick={() => void disconnect(item, language.t("provider.connect.opencode.name"))}
+                                >
+                                  {language.t("common.disconnect")}
+                                </Button>
+                              }
                            >
-                              {language.t("common.disconnect")}
-                            </Button>
+                              <AccountMenu provider={item} name={language.t("provider.connect.opencode.name")} />
+                            </Show>
                          </div>
                          <Show when={state.consoleExpanded}>
                            <div class="settings-provider-console-list">
@@ -887,6 +887,47 @@
  opacity: 1;
 }

+.settings-provider-account-trigger {
+  min-width: 0;
+  max-width: min(240px, 45%);
+}
+
+.settings-provider-account-trigger > span {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.settings-provider-account-menu[data-component="menu-v2-content"] {
+  width: min(260px, calc(100vw - 32px));
+  overflow: visible;
+}
+
+.settings-provider-account-list {
+  max-height: min(240px, calc(var(--kb-popper-content-available-height) - 120px));
+  overflow-y: auto;
+}
+
+.settings-provider-account-submenu[data-component="menu-v2-content"] {
+  width: min(260px, calc(100vw - 32px));
+  max-height: min(360px, var(--kb-popper-content-available-height));
+  overflow-y: auto;
+}
+
+.settings-provider-account-label {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+@container settings-panel (max-width: 520px) {
+  .settings-provider-account-trigger {
+    max-width: 100%;
+  }
+}
+
 .settings-providers-view-all {
  margin-top: 20px;
  padding: 0;
@@ -85,8 +85,9 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [x] Array binding and assignment destructuring from strings, Maps, Sets, URLSearchParams, custom synchronous
      iterators, and synchronous generators, including stepwise elisions/rest and `IteratorClose` on early completion
      or binding/default failure.
- [ ] Object destructuring from primitives follows ToObject (`const { length } = "abc"`, `const {} = 1`); non-object
-      sources are rejected.
+- [x] Object destructuring from primitives follows ToObject: `const { length } = "abc"` is `3`, `const { toFixed } = 1`
+      finds the built-in, `const {} = 1` is a no-op, and a rest element copies a string's indexes (`{ 1: "y", 2: "z" }`).
+      Only `null` and `undefined` sources throw (`Cannot destructure null as it is null.`).
 - [x] Destructuring reads through the prototype chain like member access: `const { constructor } = error` and
      `const { slice } = values` find the inherited built-in.
 - [x] Any assignment target as a `for...in` head, like `for...of`: `for (x.y in obj)`, `for (a[i++] in obj)`, and
@@ -130,7 +131,7 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [x] Built-in method references as callbacks, such as `values.map(Math.abs)`, `records.map(JSON.stringify)`,
      `items.forEach(console.log)`, and `Promise.resolve(-1).then(Math.abs)`. Extra callback arguments a built-in
      does not consume are ignored, like JS, and consumed arguments coerce, like JS (`"3.7".replace(/\d\.\d/,
-    Math.floor)` is `"3"`). A detached method loses its receiver, as in JS: `values.filter("abc".includes)` is a `TypeError`
+Math.floor)` is `"3"`). A detached method loses its receiver, as in JS: `values.filter("abc".includes)` is a `TypeError`
      because `includes` is called without a string `this`.
 - [x] Constructors work as callbacks with JS call semantics: `Error` types construct (`messages.map(Error)`),
      and new-requiring constructors (`Map`, `Set`, `URL`, `URLSearchParams`, `Headers`, `Promise`) throw a `TypeError`,
@@ -154,8 +155,9 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
      array, an array-like object (its `length` clamped and capped like `Array.from`), or `null`/`undefined`. A
      bound function is named `bound f`, has its remaining `length`, and is not constructible.
 - [x] `JSON.parse` revivers and `JSON.stringify` function replacers see the holder object as `this`.
- [ ] The optional `thisArg` of iteration methods (`map`, `forEach`, `Map.prototype.forEach`, `Array.from`, …) is
-      accepted but not yet passed as `this`; callbacks run with `this` undefined.
+- [x] The optional `thisArg` of the Array, Uint8Array, and `Array.from` callback methods and of Map, Set,
+      URLSearchParams, and Headers `forEach` is the callback's `this`: `[1, 2].forEach(function () { this.n++ }, c)`
+      increments `c.n` twice. Arrows ignore it, as in JS; `reduce`/`reduceRight` take an initial value instead.
 - [ ] User-defined constructor calls.
 - [ ] Classes and private fields.
 - [x] Functions are objects: they hold own properties (`fn.count = 1`), enumerate them, and expose read-only `name`
@@ -224,8 +226,8 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [x] Coercion helpers and template interpolation accept functions and namespaces: `String(fn)` and `${fn}` give
      `"[object Function]"` rather than the source text, `isNaN(fn)` is `true`.
 - [x] `==` and `!=` follow IsLooselyEqual: objects (including functions and tool references) compare by identity, a
-      nullish operand never coerces the other side, and a data object facing a primitive coerces through its built-in
-      primitive form (`fn == null` is `false`, `fn == fn` is `true`, `[1] == 1` and `[1, 2] == "1,2"` are `true`).
+      nullish operand never coerces the other side, and a data object facing a primitive converts through its own
+      `valueOf`/`toString` (default hint) (`fn == null` is `false`, `fn == fn` is `true`, `[1] == 1` and `[1, 2] == "1,2"` are `true`).
      `switch` matches cases with `===`, so `switch (fn) { case fn: }` selects, and `Object.is` compares any two
      values. Operators inspect only their direct operands, so `rows == null` on a large array costs the same as
      `rows === null`, and an object merely holding a function inside (`[fn] + ""`, `-[fn]`) coerces like any other
@@ -233,13 +235,26 @@ ultimate source of truth. Upstream test262 files run verbatim from `test/test262
 - [ ] Coercing a function, promise, generator, or tool reference itself: `fn + ""`, `-fn`, `fn++`, and `fn == 1`
      throw `TypeError: Binary operators require data values.` (or the unary/update form) where JavaScript would use
      the source text or `NaN`.
- [ ] ToPrimitive on program objects: operators, `Number`/`String`, `Error(message)`, `parseInt` radix, multi-argument
-      `Date` construction and `Date.UTC`, and numeric built-in arguments (`Math.max`, `at`, `indexOf` start) should call
-      the object's own `valueOf`/`toString` in spec order and surface their throws. Today they use the built-in form
-      (`NaN`, `"[object Object]"`) and ignore own methods. Date setters and one-argument `Date` construction already
-      follow ToPrimitive.
- [x] Property keys follow ToPropertyKey: `x[null]`, `x[true]`, and objects (via their built-in string form) become
-      string keys.
+- [x] ToPrimitive on program objects: `+ - * / % **`, the relational and bitwise operators, unary `+ - ~`, `++`/`--`,
+      compound assignment, `${x}`, `Number`/`String`/`isNaN`/`isFinite`, `parseInt`/`parseFloat` (text and radix),
+      `Math.*` arguments, `Error(message)`, and `Array.prototype.join`/`toString` elements call the object's own
+      `valueOf`/`toString` in spec order (both operands left then right, `+` with the default hint) and surface their
+      throws: `{ valueOf() { return 7 } } * 2` is `14`, `` `${{ toString() { return "x" } }}` `` is `"x"`, and
+      `[1, 2]` with `arr.toString = () => "x"` makes `arr + ""` `"x"`. Dates keep their `Symbol.toPrimitive`
+      behavior (`date + 1` concatenates, `date - date` subtracts).
+- [x] String and Number method arguments convert through ToPrimitive in spec order, receiver first: search strings,
+      separators, fills, and replacements with the string hint, indexes, counts, digits, and radixes with the number
+      hint (`"abc".indexOf({ toString() { return "b" } })` is `1`, `(255).toString({ valueOf() { return 16 } })` is
+      `"ff"`, `String.prototype.trim.call({ toString() { return " a " } })` is `"a"`). Only consumed positions
+      convert; a RegExp pattern is used as is, and `includes`/`startsWith`/`endsWith` reject one before converting.
+- [ ] ToPrimitive elsewhere: `Error.prototype.toString` on an object `message` and numeric arguments of the Array and
+      Uint8Array methods (`at`, `indexOf` start, `slice`) still use the built-in form (`NaN`, `"[object Object]"`) and
+      ignore own methods.
+- [x] Property keys follow ToPropertyKey: `x[null]` and `x[true]` become string keys, and a data object key
+      converts through its own `toString`/`valueOf` (string hint) exactly once per access, in reads, writes,
+      compound assignment, `++`, `delete`, `in`, object literals, and destructuring:
+      `o[{ toString() { return "id" } }] += 1` updates `o.id`. A nullish base throws before the key converts, as
+      in JS. Opaque values (functions, promises, tool references) keep their built-in string form.

 ## Promises and tools

@@ -300,8 +315,9 @@ reject }` object.
 - [x] `Object()` and `new Object()` return `{}` for nullish arguments and pass objects through unchanged;
      primitive wrapper objects (`Object(1)`) are rejected explicitly.
 - [x] Computed property names and object spread. Any value works as a key (ToPropertyKey): strings, numbers, and the
-      two confined symbols as themselves, everything else as its string form (`o[null]` is `o["null"]`, `o[{}]` is
-      `o["[object Object]"]`), in reads, writes, literals, `in`, and destructuring.
+      two confined symbols as themselves, data objects through their own `toString` (`o[[1, 2]]` is `o["1,2"]`), and
+      everything else as its string form (`o[null]` is `o["null"]`), in reads, writes, literals, `in`, and
+      destructuring.
 - [x] `Object.keys`, `Object.values`, `Object.entries`, `Object.hasOwn`, `Object.assign`, and `Object.fromEntries`, with
      synchronous iterator support for `fromEntries`. Sources follow ToObject: strings enumerate by index, other
      primitives and wrappers contribute nothing, and `null`/`undefined` throw. `Object.assign` accepts array
@@ -362,7 +378,6 @@ reject }` object.
      shares one prototype, where JavaScript gives each collection its own; `Object.getPrototypeOf` shows the
      difference.
 - [x] `length`, numeric indexing, index assignment, spread, and `for...of`.
- [x] The `thisArg` argument of `Array.from` is accepted and ignored, like JS arrows.
 - [x] `Array.prototype.toSpliced`.
 - [x] Canonical array/string index parsing: keys such as `"01"` are ordinary properties rather than aliases of index
      `1`.
@@ -375,8 +390,9 @@ reject }` object.
      `flat(1.9)`, `with(1.5, v)`, `Math.max("3", "2")`, `parseInt("11", "2")`, `(1.5).toFixed("2")`,
      `String.fromCharCode("65")`, and the Uint8Array equivalents. `join(sep)` and `JSON.parse(text)` apply ToString
      (`join(null)` is `"1null2"`, `JSON.parse(123)` is `123`). `Array.from({ length: "2" })` applies ToLength; a
-      promise source still throws with an `await` hint rather than JS's silent `[]`. A program object's own
-      `valueOf`/`toString` is not consulted yet (see ToPrimitive above).
+      promise source still throws with an `await` hint rather than JS's silent `[]`. `join`, `Math.*`, `parseInt`,
+      and the String and Number methods consult a program object's own `valueOf`/`toString`; the array methods do not
+      yet (see ToPrimitive above).

 ## Strings

@@ -393,14 +409,15 @@ reject }` object.
 - [x] Static `String.fromCharCode` and `String.fromCodePoint`.
 - [x] Native argument coercion for supported String methods; for example, `includes(1)` and `slice("1")` coerce like
      native JS, `split(undefined)` returns the whole string, and `includes`/`startsWith`/`endsWith` reject regular
-      expressions with a native-style `TypeError`. Opaque runtime references still reject as data errors, and
-      `repeat` still requires a finite non-negative count.
+      expressions with a native-style `TypeError`. Data objects convert through their own `toString`/`valueOf` (see
+      ToPrimitive above). Opaque runtime references still reject as data errors, and `repeat` still requires a finite
+      non-negative count.
 - [x] Native no-argument parity for `match()`, `matchAll()`, and `search()`; all behave as an empty pattern.
 - [x] `String.raw`, on a template object or any `{ raw }` object; raw strings and substitutions coerce through their own
      `toString`.
 - [x] `match`, `matchAll`, `search`, and `split` read any non-RegExp argument as a pattern string, as `new RegExp(arg)`
-      would: `"a1b".match(1)` matches `/1/`, `search(null)` looks for `"null"`, and `undefined` is the empty pattern.
-      Objects use their built-in string form until ToPrimitive lands.
+      would: `"a1b".match(1)` matches `/1/`, `search(null)` looks for `"null"`, `undefined` is the empty pattern, and
+      an object supplies its own `toString`.

 ## Numbers and Math

@@ -454,15 +471,15 @@ reject }` object.
 - [x] `getTimezoneOffset`, arithmetic, relational comparison, and `instanceof Date`.
 - [x] Date values serialize to ISO strings; invalid dates serialize to `null`.
 - [x] Local and UTC Date setters, including native argument coercion, mutation, rollover, invalid-Date recovery, and
-      `TimeClip` behavior.
+      `TimeClip` behavior. On an invalid Date every setter but `setTime` and `set(UTC)FullYear` answers `NaN` without
+      writing, so a time set inside an argument's `valueOf` survives.
 - [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.
- [x] Date setters and one-argument construction coerce object arguments through their own `valueOf`/`toString` and
-      surface their throws.
- [ ] Multi-argument construction and `Date.UTC` coerce object arguments the same way (see ToPrimitive above).
+- [x] Date setters, construction, and `Date.UTC` coerce object arguments through their own `valueOf`/`toString` in
+      argument order and surface their throws; only the first seven components are converted.
 - [x] Native Date loose-equality and default primitive-coercion semantics, using CodeMode's deterministic ISO string
      representation for the string primitive.
 - [x] Native `RangeError` branding for invalid `toISOString()` calls.
@@ -509,6 +526,11 @@ reject }` object.
 - [x] Map and Set values serialize to `{}` at host/JSON boundaries.
 - [x] Set composition and relation methods: `union`, `intersection`, `difference`, `symmetricDifference`, `isSubsetOf`,
      `isSupersetOf`, and `isDisjointFrom`, including supported Set-like operands.
+- [x] `WeakMap` (`get`, `set`, `has`, `delete`, `getOrInsert`, `getOrInsertComputed`) and `WeakSet` (`add`, `has`,
+      `delete`), constructed from iterables. Keys must be program objects: a primitive or tool reference throws
+      `Invalid value used as weak map key`, while `has`/`delete`/`get` with one answer `false`/`undefined`. Entries are
+      held by a host weak collection, so nothing is retained past the key's own lifetime. As in JS they have no `size`,
+      iteration, or `clear`, `structuredClone` rejects them, and they serialize to `{}` at host boundaries.

 ## URL and URI helpers

@@ -13,7 +13,7 @@ import {
  type Cursor,
  type Value,
 } from "./objects.js"
-import { typeofValue } from "./references.js"
+import { isOpaque, typeofValue } from "./references.js"

 /** IteratorClose: a consumer failure closes the iterator and wins over any close failure, except that a generator's
 * return() is a return completion, so a failing close wins over it, as after `break`. */
@@ -31,16 +31,15 @@ export const preserveConsumerError = <A, R>(
    })
  })

+export type Hint = "number" | "string" | "default"
+
 /**
 * ToPrimitive: calls `valueOf`/`toString` in hint order and returns the first primitive result. Dates treat the
- * default hint as "string", like their `Symbol.toPrimitive`.
+ * default hint as "string", like their `Symbol.toPrimitive`. Opaque values (functions, promises, generators, tool
+ * references) pass through unchanged so callers reject or describe them in their built-in form.
 */
-export const toPrimitive = <R>(
-  ctx: Interpreter<R>,
-  value: Value,
-  hint: "number" | "string" | "default",
-): Effect.Effect<Value, unknown, R> => {
-  if (!(value instanceof Obj)) return Effect.succeed(value)
+export const toPrimitive = <R>(ctx: Interpreter<R>, value: Value, hint: Hint): Effect.Effect<Value, unknown, R> => {
+  if (!(value instanceof Obj) || isOpaque(value)) return Effect.succeed(value)
  const asString = hint === "string" || (hint === "default" && value instanceof DateObj)
  const order = asString ? ["toString", "valueOf"] : ["valueOf", "toString"]
  return Effect.gen(function* () {
@@ -67,6 +66,28 @@ export const toPrimitiveString = <R>(ctx: Interpreter<R>, value: Value) =>
 export const toPrimitiveNumber = <R>(ctx: Interpreter<R>, value: Value) =>
  Effect.map(toPrimitive(ctx, value, "number"), coerceToNumber)

+/**
+ * Runs a native body on its arguments after ToPrimitive, in order, with one hint for all positions or one per
+ * position. Primitive arguments skip the Effect entirely.
+ */
+export const withPrimitives = <R>(
+  ctx: Interpreter<R>,
+  hints: Hint | ReadonlyArray<Hint>,
+  values: Array<Value>,
+  body: (primitives: Array<Value>) => Value | Effect.Effect<Value, unknown, R>,
+): Value | Effect.Effect<Value, unknown, R> => {
+  if (!values.some((value) => value instanceof Obj)) return body(values)
+  return Effect.flatMap(
+    Effect.forEach(values, (value, index) =>
+      toPrimitive(ctx, value, typeof hints === "string" ? hints : hints[index]!),
+    ),
+    (primitives) => {
+      const result = body(primitives)
+      return Effect.isEffect(result) ? result : Effect.succeed(result)
+    },
+  )
+}
+
 // 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
@@ -20,6 +20,7 @@ import {
  type Value,
 } from "./objects.js"
 import type { Interpreter } from "./interpreter.js"
+import { toPrimitiveString } from "./callback.js"
 import { formatValue } from "../stdlib/console.js"

 export const normalizeError = (error: unknown): Diagnostic => {
@@ -139,14 +140,13 @@ const constructAggregateErrorValue = <R>(
  proto: Obj,
 ): Effect.Effect<ErrorObj, unknown, R> =>
  Effect.gen(function* () {
+    const message = args[1] === undefined ? "" : yield* toPrimitiveString(ctx, args[1])
    const cursor = yield* ctx.iterate(args[0])
    if (cursor === undefined) throw typeError("new AggregateError(...) expects a synchronous iterable of errors.")
    const errors: Array<Value> = []
    while (true) {
      const step = yield* cursor.next
-      if (step.done) {
-        return createAggregateErrorValue(ctx, errors, args[1] === undefined ? "" : coerceToString(args[1]), proto)
-      }
+      if (step.done) return createAggregateErrorValue(ctx, errors, message, proto)
      errors.push(step.value)
    }
  })
@@ -160,7 +160,9 @@ export const errorGlobal = <R>(type: ErrorType, ctx: Interpreter<R>) => {
    const created =
      type === "AggregateError"
        ? constructAggregateErrorValue(ctx, args, proto)
-        : Effect.sync(() => createErrorValue(proto, args[0] === undefined ? undefined : coerceToString(args[0])))
+        : Effect.map(args[0] === undefined ? Effect.undefined : toPrimitiveString(ctx, args[0]), (message) =>
+            createErrorValue(proto, message),
+          )
    // ES2022 `new Error(message, { cause })`: installed only when the options object has the property at all.
    const options = args[type === "AggregateError" ? 2 : 1]
    if (!(options instanceof Obj) || !has(options, "cause")) return created
@@ -2,7 +2,7 @@ import { Effect } from "effect"
 import { Arr, Callable, coerceToInteger, coerceToString, get, Obj, 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"
+import { mapGlobal, setGlobal, weakMapGlobal, weakSetGlobal } from "../stdlib/collections.js"
 import { consoleGlobal } from "../stdlib/console.js"
 import { dateGlobal } from "../stdlib/date.js"
 import { jsonGlobal } from "../stdlib/json.js"
@@ -111,6 +111,8 @@ const table: Record<string, Factory> = {
  RegExp: (ctx) => regexpGlobal(ctx),
  Map: (ctx) => mapGlobal(ctx),
  Set: (ctx) => setGlobal(ctx),
+  WeakMap: (ctx) => weakMapGlobal(ctx),
+  WeakSet: (ctx) => weakSetGlobal(ctx),
  URL: (ctx) => urlGlobal(ctx),
  URLSearchParams: (ctx) => urlSearchParamsGlobal(ctx),
  Headers: (ctx) => headersGlobal(ctx),
@@ -95,7 +95,7 @@ import {
  coerceToString,
  type Value,
 } from "./objects.js"
-import { preserveConsumerError } from "./callback.js"
+import { type Hint, preserveConsumerError, toPrimitive } from "./callback.js"
 import { Pending, resolvePromise, resolvePromiseValue } from "./promises.js"
 import { describeValue, isOpaque, rejectCircularInsertion, typeofValue } from "./references.js"
 import { ScopeStack } from "./scope.js"
@@ -103,6 +103,30 @@ import { constructRegExp } from "../stdlib/regexp.js"
 import { enumerableSource } from "../stdlib/object.js"
 import { compoundOperators } from "../stdlib/value.js"

+/** The binary operators that convert object operands through ToPrimitive before acting on primitives. */
+const primitiveOperators = new Set([
+  "+",
+  "-",
+  "*",
+  "/",
+  "%",
+  "**",
+  "<",
+  "<=",
+  ">",
+  ">=",
+  "&",
+  "|",
+  "^",
+  "<<",
+  ">>",
+  ">>>",
+])
+
+/** ToPropertyKey on a primitive (or an opaque value, which keeps its built-in string form). */
+const propertyKey = (value: Value): PropertyKey =>
+  typeof value === "string" || typeof value === "number" || typeof value === "symbol" ? value : coerceToString(value)
+
 // 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.
 const loopExit = (result: StatementResult, labels: ReadonlySet<string> | undefined): StatementResult | undefined => {
@@ -1116,18 +1140,15 @@ class Frame<R> {
      }

      if (pattern.type === "ObjectPattern") {
-        if (!(value instanceof Obj)) {
-          throw typeError(
-            `Object destructuring requires a data object or array value, received ${describeValue(value)}.`,
-            pattern,
-          )
+        if (value === null || value === undefined) {
+          throw typeError(`Cannot destructure ${describeValue(value)} as it is ${value}.`, pattern)
        }

        const consumed = new Set<PropertyKey>()
        for (const property of pattern.properties) {
          if (property.type === "RestElement") {
            const rest = new Obj(self.ctx.builtins.Object)
-            assign(rest, value, consumed)
+            assign(rest, enumerableSource(self.ctx, "Object destructuring", value, pattern), consumed)
            yield* self.declarePattern(property.argument, rest, mutable, property, initialize)
            continue
          }
@@ -1136,7 +1157,7 @@ class Frame<R> {
          consumed.add(typeof key === "symbol" ? key : String(key))
          yield* self.declarePattern(
            property.value,
-            self.readProperty(value, key, property),
+            self.destructuredProperty(value, key, property),
            mutable,
            property,
            initialize,
@@ -1175,24 +1196,21 @@ class Frame<R> {
      }

      if (pattern.type === "ObjectPattern") {
-        if (!(value instanceof Obj)) {
-          throw invalidData(
-            `Object destructuring requires a data object or array value, received ${describeValue(value)}.`,
-            pattern,
-          )
+        if (value === null || value === undefined) {
+          throw typeError(`Cannot destructure ${describeValue(value)} as it is ${value}.`, pattern)
        }

        const consumed = new Set<PropertyKey>()
        for (const property of pattern.properties) {
          if (property.type === "RestElement") {
            const rest = new Obj(self.ctx.builtins.Object)
-            assign(rest, value, consumed)
+            assign(rest, enumerableSource(self.ctx, "Object destructuring", value, pattern), consumed)
            yield* self.assignPattern(property.argument, rest, property)
            continue
          }
          const key = yield* self.destructuringPropertyKey(property)
          consumed.add(typeof key === "symbol" ? key : String(key))
-          yield* self.assignPattern(property.value, self.readProperty(value, key, property), property)
+          yield* self.assignPattern(property.value, self.destructuredProperty(value, key, property), property)
        }
        return
      }
@@ -1263,7 +1281,7 @@ class Frame<R> {
    }
    const keyNode = property.key
    if (property.computed) {
-      return Effect.map(this.evaluateExpression(keyNode), (value) => this.toPropertyKey(value))
+      return Effect.flatMap(this.evaluateExpression(keyNode), (value) => this.toPropertyKey(value, keyNode))
    }
    if (keyNode.type === "Identifier") return Effect.succeed(keyNode.name)
    if (keyNode.type === "Literal") return Effect.succeed(String(keyNode.value))
@@ -1368,85 +1386,105 @@ class Frame<R> {
      const lhs = yield* self.evaluateExpression(left)
      const rhs = yield* self.evaluateExpression(node.right)
      if (operator === "instanceof") return instanceofValue(lhs, rhs, node)
+      if (lhs instanceof Obj || rhs instanceof Obj) return yield* self.applyOperator(operator, lhs, rhs, node)
      return self.applyBinaryOperator(operator, lhs, rhs, node)
    })
  }

+  /** ToPrimitive for an operand: data objects run their own methods; opaque values stay for the data gates below. */
+  private toPrimitive(value: Value, hint: Hint, node: AstNode) {
+    return this.native(() => toPrimitive(this.ctx, value, hint), node)
+  }
+
+  // Arithmetic, relational, and bitwise operators convert both operands first, left then right, so a `valueOf`
+  // runs (and throws) in spec order; `+` asks for the default hint and the rest for a number.
+  private applyOperator(operator: string, lhs: Value, rhs: Value, node: AstNode): Effect.Effect<Value, unknown, R> {
+    if (!(lhs instanceof Obj || rhs instanceof Obj))
+      return Effect.succeed(this.applyBinaryOperator(operator, lhs, rhs, node))
+    // IsLooselyEqual converts only an object facing a non-nullish primitive; two objects (including tool
+    // references, which are not Obj) compare by identity.
+    const equality = operator === "==" || operator === "!="
+    // `in` checks the right operand before ToPropertyKey on the left, so a bad right side wins over a bad key.
+    if (operator === "in" && lhs instanceof Obj && !isOpaque(lhs) && rhs instanceof Obj) {
+      return Effect.map(this.toPropertyKey(lhs, node), (key) => has(rhs, key))
+    }
+    const other = lhs instanceof Obj ? rhs : lhs
+    const converts =
+      primitiveOperators.has(operator) ||
+      (equality && other !== null && other !== undefined && typeof other !== "object")
+    if (!converts) return Effect.succeed(this.applyBinaryOperator(operator, lhs, rhs, node))
+    const hint = operator === "+" || equality ? "default" : "number"
+    const self = this
+    return Effect.gen(function* () {
+      const l = yield* self.toPrimitive(lhs, hint, node)
+      const r = yield* self.toPrimitive(rhs, hint, node)
+      return self.applyBinaryOperator(operator, l, r, node)
+    })
+  }
+
  private applyBinaryOperator(operator: string, lhs: Value, rhs: Value, node: AstNode): Value {
    if (operator === "===") return lhs === rhs
    if (operator === "!==") return lhs !== rhs
    if (operator === "==") return this.looselyEqual(lhs, rhs, node)
    if (operator === "!=") return !this.looselyEqual(lhs, rhs, node)
-    if (operator === "in" && rhs instanceof Obj && !isOpaque(lhs)) {
-      return has(rhs, lhs !== null && typeof lhs === "object" ? coerceToString(lhs) : (lhs as PropertyKey))
-    }
+    if (operator === "in" && rhs instanceof Obj && !isOpaque(lhs)) return has(rhs, propertyKey(lhs))
    if (isOpaque(lhs) || isOpaque(rhs)) {
      throw invalidData("Binary operators require data values.", node)
    }
-    // Addition uses the default hint; every other operator asks for a number.
-    const hint = operator === "+" ? "default" : "number"
-    const coerceOperand = (operand: Value) => (operand instanceof Obj ? operand.toPrimitive(hint) : operand)
-    const l = coerceOperand(lhs)
-    const r = coerceOperand(rhs)
+    // Object operands were already converted by applyOperator; only primitives reach the arithmetic below.
    switch (operator) {
      case "+": {
-        const sum = (l as string) + (r as string)
+        const sum = (lhs as string) + (rhs as string)
        if (typeof sum === "string") checkStringLength(sum.length)
        return sum
      }
      case "-":
-        return (l as number) - (r as number)
+        return (lhs as number) - (rhs as number)
      case "*":
-        return (l as number) * (r as number)
+        return (lhs as number) * (rhs as number)
      case "/":
-        return (l as number) / (r as number)
+        return (lhs as number) / (rhs as number)
      case "%":
-        return (l as number) % (r as number)
+        return (lhs as number) % (rhs as number)
      case "**":
-        return (l as number) ** (r as number)
+        return (lhs as number) ** (rhs as number)
      case "<":
-        return (l as string) < (r as string)
+        return (lhs as string) < (rhs as string)
      case "<=":
-        return (l as string) <= (r as string)
+        return (lhs as string) <= (rhs as string)
      case ">":
-        return (l as string) > (r as string)
+        return (lhs as string) > (rhs as string)
      case ">=":
-        return (l as string) >= (r as string)
+        return (lhs as string) >= (rhs as string)
      case "&":
-        return (l as number) & (r as number)
+        return (lhs as number) & (rhs as number)
      case "|":
-        return (l as number) | (r as number)
+        return (lhs as number) | (rhs as number)
      case "^":
-        return (l as number) ^ (r as number)
+        return (lhs as number) ^ (rhs as number)
      case "<<":
-        return (l as number) << (r as number)
+        return (lhs as number) << (rhs as number)
      case ">>":
-        return (l as number) >> (r as number)
+        return (lhs as number) >> (rhs as number)
      case ">>>":
-        return (l as number) >>> (r as number)
+        return (lhs as number) >>> (rhs as number)
      case "in":
-        if (!(rhs instanceof Obj)) {
-          throw typeError("The 'in' operator requires a data object on the right-hand side.", node)
-        }
-        return has(rhs, coerceOperand(lhs) as PropertyKey)
+        throw typeError("The 'in' operator requires a data object on the right-hand side.", node)
      default:
        throw typeError(`Unsupported binary operator '${operator}'.`, node)
    }
  }

-  // IsLooselyEqual: objects (including functions and tool references) compare by identity, and only a
-  // data object facing a non-nullish primitive needs to coerce, so an opaque value is rejected only there.
+  // IsLooselyEqual: objects (including functions and tool references) compare by identity, and a nullish
+  // primitive never equals an object.
  private looselyEqual(lhs: Value, rhs: Value, node: AstNode): boolean {
    const lhsObject = lhs !== null && typeof lhs === "object"
    const rhsObject = rhs !== null && typeof rhs === "object"
    if (lhsObject === rhsObject) return lhsObject ? lhs === rhs : lhs == rhs
-    const object = lhsObject ? lhs : rhs
    const primitive = lhsObject ? rhs : lhs
    if (primitive === null || primitive === undefined) return false
-    if (!(object instanceof Obj) || isOpaque(object)) {
-      throw invalidData("Binary operators require data values.", node)
-    }
-    return object.toPrimitive("default") == primitive
+    // Data objects were converted by applyOperator, so only an opaque reference facing a primitive gets here.
+    throw invalidData("Binary operators require data values.", node)
  }

  private evaluateLogicalExpression(node: LogicalExpression): Effect.Effect<Value, unknown, R> {
@@ -1468,14 +1506,16 @@ class Frame<R> {
    if (operator === "typeof" && argument.type === "Identifier" && !this.scopes.resolve(argument.name)) {
      return Effect.succeed("undefined")
    }
-    return Effect.map(this.evaluateExpression(argument), (value) => {
+    const self = this
+    return Effect.gen(function* () {
+      const value = yield* self.evaluateExpression(argument)
      if (operator === "typeof") return typeofValue(value)
      if (operator === "!") return !value
      if (operator === "void") return undefined
-      if (isOpaque(value)) {
+      const operand = yield* self.toPrimitive(value, "number", node)
+      if (isOpaque(operand)) {
        throw invalidData("Unary operators require data values.", node)
      }
-      const operand = value instanceof Obj ? value.toPrimitive("number") : value
      let result: Value
      switch (operator) {
        case "+":
@@ -1497,11 +1537,16 @@ class Frame<R> {
  private evaluateAssignmentExpression(node: AssignmentExpression): Effect.Effect<Value, unknown, R> {
    const left = node.left
    const operator = node.operator
+    // The binary operator a compound assignment applies: `+=` is `+`.
+    const binary = operator.slice(0, -1)
    const self = this
    return Effect.gen(function* () {
      if (operator === "??=" || operator === "||=" || operator === "&&=") {
        return yield* self.evaluateLogicalAssignment(node, left, operator)
      }
+      if (operator !== "=" && !compoundOperators.has(operator)) {
+        throw typeError(`Unsupported assignment operator '${operator}'.`, node)
+      }
      if (operator === "=" && (left.type === "ObjectPattern" || left.type === "ArrayPattern")) {
        const rightValue = yield* self.evaluateExpression(node.right)
        yield* self.assignPattern(left, rightValue, node)
@@ -1512,17 +1557,24 @@ class Frame<R> {
        if (operator !== "=") {
          const current = self.scopes.get(name, left)
          const rightValue = yield* self.evaluateExpression(node.right)
-          return self.scopes.set(name, self.applyCompoundAssignment(operator, current, rightValue, node), left)
+          const next =
+            current instanceof Obj || rightValue instanceof Obj
+              ? yield* self.applyOperator(binary, current, rightValue, node)
+              : self.applyBinaryOperator(binary, current, rightValue, node)
+          return self.scopes.set(name, next, left)
        }
        const rightValue = yield* self.evaluateNamed(node.right, name)
        return self.scopes.set(name, rightValue, left)
      }
      if (left.type === "MemberExpression") {
        return yield* self.modifyMember(left, (current) =>
-          Effect.map(self.evaluateExpression(node.right), (rightValue) => {
-            if (operator === "=") return { write: true, next: rightValue, result: rightValue }
-            const next = self.applyCompoundAssignment(operator, current, rightValue, node)
-            return { write: true, next, result: next }
+          Effect.flatMap(self.evaluateExpression(node.right), (rightValue) => {
+            if (operator === "=") return Effect.succeed({ write: true, next: rightValue, result: rightValue })
+            return Effect.map(self.applyOperator(binary, current, rightValue, node), (next) => ({
+              write: true,
+              next,
+              result: next,
+            }))
          }),
        )
      }
@@ -1572,8 +1624,7 @@ class Frame<R> {
      throw typeError(`Unsupported update operator '${operator}'.`, node)
    }

-    // CodeMode numeric coercion, not host Number(): null-prototype data objects would make
-    // the host throw during ToPrimitive, and opaque runtime references must reject clearly.
+    // CodeMode numeric coercion, not host Number(), so opaque runtime references reject clearly.
    const operand = (current: Value): number => {
      if (isOpaque(current)) {
        throw invalidData(`'${operator}' requires a data value.`, argument)
@@ -1582,21 +1633,26 @@ class Frame<R> {
    }

    if (argument.type === "Identifier") {
-      return Effect.sync(() => {
-        const name = argument.name
-        const current = operand(this.scopes.get(name, argument))
-        const next = current + increment
+      const name = argument.name
+      const current = this.scopes.get(name, argument)
+      const update = (value: Value) => {
+        const before = operand(value)
+        const next = before + increment
        this.scopes.set(name, next, argument)
-        return prefix ? next : current
-      })
+        return prefix ? next : before
+      }
+      if (!(current instanceof Obj)) return Effect.sync(() => update(current))
+      return Effect.map(this.toPrimitive(current, "number", argument), update)
    }

    if (argument.type === "MemberExpression") {
-      return this.modifyMember(argument, (current) => {
-        const value = operand(current)
-        const next = value + increment
-        return Effect.succeed({ write: true, next, result: prefix ? next : value })
-      })
+      return this.modifyMember(argument, (current) =>
+        Effect.map(this.toPrimitive(current, "number", argument), (primitive) => {
+          const value = operand(primitive)
+          const next = value + increment
+          return { write: true, next, result: prefix ? next : value }
+        }),
+      )
    }

    throw typeError("Update target must be an Identifier or MemberExpression.", argument)
@@ -1996,11 +2052,11 @@ class Frame<R> {
        let key: PropertyKey

        if (property.computed) {
-          key = self.toPropertyKey(yield* self.evaluateExpression(keyNode))
+          key = yield* self.toPropertyKey(yield* self.evaluateExpression(keyNode), keyNode)
        } else if (keyNode.type === "Identifier") {
          key = keyNode.name
        } else if (keyNode.type === "Literal") {
-          key = self.toPropertyKey(literal(keyNode))
+          key = propertyKey(literal(keyNode))
        } else {
          throw typeError("Unsupported object property key shape.", keyNode)
        }
@@ -2065,7 +2121,7 @@ class Frame<R> {

        if (index < expressions.length) {
          const raw = yield* self.evaluateExpression(expressions[index])
-          output += coerceToString(raw)
+          output += coerceToString(yield* self.toPrimitive(raw, "string", expressions[index]))
          checkStringLength(output.length)
        }
      }
@@ -2115,13 +2171,6 @@ class Frame<R> {
    )
  }

-  private applyCompoundAssignment(operator: string, current: Value, incoming: Value, node: AstNode): Value {
-    if (!compoundOperators.has(operator)) {
-      throw typeError(`Unsupported assignment operator '${operator}'.`, node)
-    }
-    return this.applyBinaryOperator(operator.slice(0, -1), current, incoming, node)
-  }
-
  private getMemberReference(
    node: MemberExpression,
  ): Effect.Effect<MemberReference | ToolReference | { value: Value } | typeof OptionalShortCircuit, unknown, R> {
@@ -2135,37 +2184,58 @@ class Frame<R> {
      if (objectValue === OptionalShortCircuit) return OptionalShortCircuit
      if ((objectValue === null || objectValue === undefined) && node.optional) return OptionalShortCircuit

-      const key = node.computed
-        ? self.toPropertyKey(yield* self.evaluateExpression(propertyNode))
-        : propertyNode.type === "Identifier"
+      const keyValue =
+        !node.computed && propertyNode.type === "Identifier"
          ? propertyNode.name
-          : self.toPropertyKey(yield* self.evaluateExpression(propertyNode))
-
-      if (objectValue instanceof ToolReference) {
-        if (typeof key !== "string") {
-          throw typeError("Tool paths must use string property names.", propertyNode)
-        }
-        return new ToolReference([...objectValue.path, key])
-      }
-
-      if (objectValue instanceof Obj) return { target: objectValue, key, receiver: objectValue }
-
-      // 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] }
-      }
-      const proto = primitivePrototype(self.ctx.builtins, objectValue)
-      if (proto !== undefined) return { target: proto, key, receiver: objectValue }
-
+          : yield* self.evaluateExpression(propertyNode)
+      // GetValue applies ToObject to the base before ToPropertyKey, so a nullish base throws before the key's own
+      // toString runs.
      if (objectValue === null || objectValue === undefined) {
-        throw typeError(`Cannot read properties of ${objectValue} (reading '${String(key)}').`, objectNode)
+        throw typeError(`Cannot read properties of ${objectValue} (reading '${coerceToString(keyValue)}').`, objectNode)
      }
-      throw typeError("Cannot access a property on a non-object value.", objectNode)
+      const key = yield* self.toPropertyKey(keyValue, propertyNode)
+      return self.resolveProperty(objectValue, key, objectNode, propertyNode)
    })
  }

+  private resolveProperty(
+    objectValue: Value,
+    key: PropertyKey,
+    objectNode: AstNode,
+    propertyNode: AstNode,
+  ): MemberReference | ToolReference | { value: Value } {
+    if (objectValue instanceof ToolReference) {
+      if (typeof key !== "string") {
+        throw typeError("Tool paths must use string property names.", propertyNode)
+      }
+      return new ToolReference([...objectValue.path, key])
+    }
+
+    if (objectValue instanceof Obj) return { target: objectValue, key, receiver: objectValue }
+
+    // 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] }
+    }
+    const proto = primitivePrototype(this.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)
+    }
+    throw typeError("Cannot access a property on a non-object value.", objectNode)
+  }
+
+  // One destructured property, read the way a member expression would read it (primitives use their prototype).
+  private destructuredProperty(source: Value, key: PropertyKey, node: AstNode): Value {
+    const reference = this.resolveProperty(source, key, node, node)
+    if (reference instanceof ToolReference) return reference
+    if ("value" in reference) return reference.value
+    return this.readProperty(reference.target, reference.key, node, reference.receiver)
+  }
+
  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)) {
@@ -2255,9 +2325,10 @@ class Frame<R> {
    throw typeError(`Cannot assign to read only property '${String(key)}'.`, node)
  }

-  // ToPropertyKey: anything else becomes its string form, so `counts[row.category]` works when the field is null.
-  private toPropertyKey(value: Value): PropertyKey {
-    if (typeof value === "string" || typeof value === "number" || typeof value === "symbol") return value
-    return coerceToString(value)
+  // ToPropertyKey: a data object converts through its own `toString`/`valueOf` first; anything else becomes its
+  // string form synchronously, so `counts[row.category]` works when the field is null.
+  private toPropertyKey(value: Value, node: AstNode): Effect.Effect<PropertyKey, unknown, R> {
+    if (!(value instanceof Obj)) return Effect.succeed(propertyKey(value))
+    return Effect.map(this.toPrimitive(value, "string", node), propertyKey)
  }
 }
@@ -27,6 +27,8 @@ const builtins = [
  "RegExp",
  "Map",
  "Set",
+  "WeakMap",
+  "WeakSet",
  "URL",
  "URLSearchParams",
  "Headers",
@@ -88,6 +90,8 @@ export const createBuiltins = (): Builtins => {
    RegExp: plain(),
    Map: plain(),
    Set: plain(),
+    WeakMap: plain(),
+    WeakSet: plain(),
    URL: plain(),
    URLSearchParams: plain(),
    Headers: plain(),
@@ -356,6 +356,23 @@ export class SetObj extends Wrapper {
  }
 }

+/** Keys are program objects, so a host WeakMap gives the same lifetime rule as JavaScript without any bookkeeping. */
+export class WeakMapObj extends Wrapper {
+  override readonly tag = "WeakMap"
+  readonly map = new WeakMap<Obj, Value>()
+  override inspect() {
+    return "WeakMap { <items unknown> }"
+  }
+}
+
+export class WeakSetObj extends Wrapper {
+  override readonly tag = "WeakSet"
+  readonly set = new WeakSet<Obj>()
+  override inspect() {
+    return "WeakSet { <items unknown> }"
+  }
+}
+
 export class URLSearchParamsObj extends Wrapper {
  override readonly tag = "URLSearchParams"
  constructor(
@@ -18,7 +18,7 @@ import {
  type Value,
 } from "../interpreter/objects.js"
 import { describeValue, rejectCircularInsertion } from "../interpreter/references.js"
-import { applyCollectionCallback, invoke, preserveConsumerError } from "../interpreter/callback.js"
+import { applyCollectionCallback, invoke, preserveConsumerError, withPrimitives } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
 import { compareText } from "../tool-runtime.js"

@@ -49,7 +49,7 @@ const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<Value>): Effect.Effect<Va
      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]))
+        values.push(apply === undefined ? item : yield* apply([item, index], args[2]))
      }
      return new Arr(proto, values)
    }
@@ -59,7 +59,9 @@ const arrayFrom = <R>(ctx: Interpreter<R>, args: Array<Value>): Effect.Effect<Va
      const step = yield* cursor.next
      if (step.done) return new Arr(proto, values)
      values.push(
-        apply === undefined ? step.value : yield* preserveConsumerError(cursor.close, apply([step.value, index])),
+        apply === undefined
+          ? step.value
+          : yield* preserveConsumerError(cursor.close, apply([step.value, index], args[2])),
      )
      index += 1
    }
@@ -146,20 +148,30 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
      "join",
      1,
      (thisValue, args) => {
-        const joined = self(thisValue, "join")
-          .items.map((item) => coerceToString(item ?? ""))
-          .join(args[0] === undefined ? "," : coerceToString(args[0]))
-        checkStringLength(joined.length)
-        return joined
+        // .map would keep holes, which Effect.forEach would then hand to the body as undefined.
+        const parts = Array.from(self(thisValue, "join").items, (item) => item ?? "")
+        return withPrimitives(
+          ctx,
+          "string",
+          [args[0] === undefined ? "," : args[0], ...parts],
+          ([separator, ...items]) => {
+            const joined = items.map(coerceToString).join(coerceToString(separator))
+            checkStringLength(joined.length)
+            return joined
+          },
+        )
      },
    ],
    [
      "toString",
      0,
      (thisValue) =>
-        self(thisValue, "toString")
-          .items.map((item) => coerceToString(item ?? ""))
-          .join(","),
+        withPrimitives(
+          ctx,
+          "string",
+          Array.from(self(thisValue, "toString").items, (item) => item ?? ""),
+          (items) => items.map(coerceToString).join(","),
+        ),
    ],
    [
      "includes",
@@ -362,7 +374,7 @@ export const arrayGlobal = <R>(ctx: Interpreter<R>) => {
          const values: Array<Value> = []
          for (let index = 0; index < length; index += 1) {
            if (!(index in target.items)) continue
-            const mapped = yield* apply([target.items[index], index, target])
+            const mapped = yield* apply([target.items[index], index, target], args[1])
            if (mapped instanceof Arr) values.push(...mapped.items)
            else values.push(mapped)
          }
@@ -401,7 +413,10 @@ export const callbackMethods = <R, T extends Obj>(
    length,
    (thisValue, args) => {
      const target = self(thisValue, name)
-      return body(elements(target), target, applyCollectionCallback(ctx, args[0], `${label}.${name}`), args)
+      const call = applyCollectionCallback(ctx, args[0], `${label}.${name}`)
+      // reduce and reduceRight take an initial value where the others take a thisArg.
+      const thisArg = name.startsWith("reduce") ? undefined : args[1]
+      return body(elements(target), target, (callbackArgs) => call(callbackArgs, thisArg), args)
    },
  ]
  return [
@@ -16,6 +16,8 @@ import {
  PromiseObj,
  SetObj,
  type Value,
+  WeakMapObj,
+  WeakSetObj,
 } from "../interpreter/objects.js"
 import { describeValue, isOpaque } from "../interpreter/references.js"
 import {
@@ -188,7 +190,7 @@ export const mapGlobal = <R>(ctx: Interpreter<R>) => {
        const target = self(thisValue, "forEach")
        const apply = applyCollectionCallback(ctx, args[0], "Map.forEach")
        return Effect.gen(function* () {
-          for (const [key, item] of target.map.entries()) yield* apply([item, key, target])
+          for (const [key, item] of target.map.entries()) yield* apply([item, key, target], args[1])
          return undefined
        })
      },
@@ -386,7 +388,7 @@ export const setGlobal = <R>(ctx: Interpreter<R>) => {
        const target = self(thisValue, "forEach")
        const apply = applyCollectionCallback(ctx, args[0], "Set.forEach")
        return Effect.gen(function* () {
-          for (const item of target.set.values()) yield* apply([item, item, target])
+          for (const item of target.set.values()) yield* apply([item, item, target], args[1])
          return undefined
        })
      },
@@ -402,3 +404,134 @@ export const setGlobal = <R>(ctx: Interpreter<R>) => {
  define(proto, IteratorSymbol, get(proto, "values"), hidden)
  return set
 }
+
+// CanBeHeldWeakly: only program objects; tool references are rebuilt on every access, so they could never be found again.
+const weakKey = (value: Value, label: string) => {
+  if (value instanceof Obj) return value
+  throw typeError(`Invalid value used ${label}: ${describeValue(value)} cannot be held weakly.`)
+}
+
+export const weakMapGlobal = <R>(ctx: Interpreter<R>) => {
+  const builtins = ctx.builtins
+  const proto = builtins.WeakMap
+  const weakMap = constructor<R>(builtins, proto, {
+    name: "WeakMap",
+    call: requiresNew("WeakMap"),
+    construct: (args, newTarget) => {
+      const target = new WeakMapObj(prototypeFrom(newTarget, proto))
+      if (args[0] === undefined || args[0] === null) return Effect.succeed(target)
+      return Effect.gen(function* () {
+        const cursor = yield* ctx.iterate(args[0]!)
+        if (cursor === undefined) {
+          throw typeError(
+            `new WeakMap(...) expects an iterable of [key, value] pairs, received ${describeValue(args[0])}.`,
+          )
+        }
+        while (true) {
+          const step = yield* cursor.next
+          if (step.done) return target
+          yield* preserveConsumerError(
+            cursor.close,
+            Effect.sync(() => {
+              if (!(step.value instanceof Obj)) {
+                throw typeError("new WeakMap(...) expects [key, value] pairs as entry objects.")
+              }
+              target.map.set(weakKey(getOwn(step.value, 0), "as weak map key"), getOwn(step.value, 1))
+            }),
+          )
+        }
+      })
+    },
+  })
+  const self = (thisValue: Value, name: string) => receiver(WeakMapObj, thisValue, `WeakMap.prototype.${name}`).map
+  // Lookups pass any key through: the host collection answers false for a non-object, as the spec requires.
+  const key = (value: Value) => weakKey(value, "as weak map key")
+  methods(builtins, proto, [
+    [
+      "get",
+      1,
+      (thisValue, args) => {
+        const target = self(thisValue, "get")
+        return args[0] instanceof Obj ? target.get(args[0]) : undefined
+      },
+    ],
+    ["has", 1, (thisValue, args) => self(thisValue, "has").has(args[0] as Obj)],
+    ["delete", 1, (thisValue, args) => self(thisValue, "delete").delete(args[0] as Obj)],
+    [
+      "set",
+      2,
+      (thisValue, args) => {
+        self(thisValue, "set").set(key(args[0]), args[1])
+        return thisValue
+      },
+    ],
+    [
+      "getOrInsert",
+      2,
+      (thisValue, args) => {
+        const target = self(thisValue, "getOrInsert")
+        const k = key(args[0])
+        if (!target.has(k)) target.set(k, args[1])
+        return target.get(k)
+      },
+    ],
+    [
+      "getOrInsertComputed",
+      2,
+      (thisValue, args) => {
+        const target = self(thisValue, "getOrInsertComputed")
+        const k = key(args[0])
+        const apply = applyCollectionCallback(ctx, args[1], "WeakMap.getOrInsertComputed")
+        if (target.has(k)) return target.get(k)
+        return Effect.map(apply([k]), (value) => {
+          target.set(k, value)
+          return value
+        })
+      },
+    ],
+  ])
+  return weakMap
+}
+
+export const weakSetGlobal = <R>(ctx: Interpreter<R>) => {
+  const builtins = ctx.builtins
+  const proto = builtins.WeakSet
+  const weakSet = constructor<R>(builtins, proto, {
+    name: "WeakSet",
+    call: requiresNew("WeakSet"),
+    construct: (args, newTarget) => {
+      const target = new WeakSetObj(prototypeFrom(newTarget, proto))
+      if (args[0] === undefined || args[0] === null) return Effect.succeed(target)
+      return Effect.gen(function* () {
+        const cursor = yield* ctx.iterate(args[0]!)
+        if (cursor === undefined) {
+          throw typeError(`new WeakSet(...) expects a synchronous iterable, received ${describeValue(args[0])}.`)
+        }
+        while (true) {
+          const step = yield* cursor.next
+          if (step.done) return target
+          yield* preserveConsumerError(
+            cursor.close,
+            Effect.sync(() => {
+              target.set.add(weakKey(step.value, "in weak set"))
+            }),
+          )
+        }
+      })
+    },
+  })
+  const self = (thisValue: Value, name: string) => receiver(WeakSetObj, thisValue, `WeakSet.prototype.${name}`).set
+  methods(builtins, proto, [
+    ["has", 1, (thisValue, args) => self(thisValue, "has").has(args[0] as Obj)],
+    ["delete", 1, (thisValue, args) => self(thisValue, "delete").delete(args[0] as Obj)],
+    [
+      "add",
+      1,
+      (thisValue, args) => {
+        self(thisValue, "add").add(weakKey(args[0], "in weak set"))
+        return thisValue
+      },
+    ],
+  ])
+  return weakSet
+}
@@ -16,8 +16,11 @@ const constructDate = <R>(ctx: Interpreter<R>, args: Array<Value>, proto: Obj) =
        : new DateObj(proto, new Date(coerceToNumber(value)).getTime()),
    )
  }
-  const parts = args.map((arg) => coerceToNumber(arg))
-  return Effect.succeed(new DateObj(proto, new Date(...(parts as [number, number])).getTime()))
+  // The spec converts at most seven components, in order, so extra arguments never run program code.
+  return Effect.map(
+    Effect.forEach(args.slice(0, 7), (arg) => toPrimitiveNumber(ctx, arg), { concurrency: 1 }),
+    (parts) => new DateObj(proto, new Date(...(parts as [number, number])).getTime()),
+  )
 }

 type Getter = keyof {
@@ -79,7 +82,15 @@ export const dateGlobal = <R>(ctx: Interpreter<R>) => {
  methods(builtins, date, [
    ["now", 0, () => Date.now()],
    ["parse", 1, (_, args) => Date.parse(coerceToString(args[0]))],
-    ["UTC", 7, (_, args) => Date.UTC(...(args.map((arg) => coerceToNumber(arg)) as Parameters<typeof Date.UTC>))],
+    [
+      "UTC",
+      7,
+      (_, args) =>
+        Effect.map(
+          Effect.forEach(args.slice(0, 7), (arg) => toPrimitiveNumber(ctx, arg), { concurrency: 1 }),
+          (parts) => Date.UTC(...(parts as Parameters<typeof Date.UTC>)),
+        ),
+    ],
  ])

  const self = (thisValue: Value, name: string) => receiver(DateObj, thisValue, `Date.prototype.${name}`)
@@ -125,6 +136,8 @@ export const dateGlobal = <R>(ctx: Interpreter<R>) => {
              concurrency: 1,
            }),
            (values) => {
+              // Every setter but setTime and setFullYear leaves an invalid Date untouched and answers NaN.
+              if (Number.isNaN(hosted.getTime()) && name !== "setTime" && !name.endsWith("FullYear")) return NaN
              target.time = hosted[name](...(values as [number, number, number, number]))
              return target.time
            },
@@ -117,7 +117,7 @@ export const headersGlobal = <R>(ctx: Interpreter<R>) => {
        const target = self(thisValue, "forEach")
        const apply = applyCollectionCallback(ctx, args[0], "Headers.forEach")
        return Effect.gen(function* () {
-          for (const [key, value] of Array.from(target.headers.entries())) yield* apply([value, key, target])
+          for (const [key, value] of Array.from(target.headers.entries())) yield* apply([value, key, target], args[1])
          return undefined
        })
      },
@@ -2,7 +2,7 @@ import { Effect } from "effect"
 import { constants, type Method, methods } from "../interpreter/native.js"
 import { typeError } from "../interpreter/model.js"
 import { Obj, coerceToNumber } from "../interpreter/objects.js"
-import { preserveConsumerError } from "../interpreter/callback.js"
+import { preserveConsumerError, withPrimitives } from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"

 // Bun exposes ES2026 Math.sumPrecise before TypeScript's standard library types.
@@ -12,25 +12,27 @@ 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 unary = (name: string, op: (a: number) => number): Method => [name, 1, (_, args) => op(coerceToNumber(args[0]))]
-
-const binary = (name: string, op: (a: number, b: number) => number): Method => [
-  name,
-  2,
-  (_, args) => op(coerceToNumber(args[0]), coerceToNumber(args[1])),
-]
-
-const variadic = (name: string, op: (...values: Array<number>) => number): Method => [
-  name,
-  2,
-  (_, args) => op(...args.map(coerceToNumber)),
-]
-
 export const mathGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
  const math = new Obj(builtins.Object)
+  // Convert only the arguments a method consumes; like JS, extras are ignored
+  // (so built-ins work as callbacks receiving (element, index, array)).
+  const unary = (name: string, op: (a: number) => number): Method => [
+    name,
+    1,
+    (_, args) => withPrimitives(ctx, "number", [args[0]], ([a]) => op(coerceToNumber(a))),
+  ]
+  const binary = (name: string, op: (a: number, b: number) => number): Method => [
+    name,
+    2,
+    (_, args) =>
+      withPrimitives(ctx, "number", [args[0], args[1]], ([a, b]) => op(coerceToNumber(a), coerceToNumber(b))),
+  ]
+  const variadic = (name: string, op: (...values: Array<number>) => number): Method => [
+    name,
+    2,
+    (_, args) => withPrimitives(ctx, "number", args, (values) => op(...values.map(coerceToNumber))),
+  ]
  constants(math, {
    PI: Math.PI,
    E: Math.E,
@@ -1,8 +1,9 @@
-import { constructor, constants, methods } from "../interpreter/native.js"
-import { coerceToNumber, coerceToString, type Value } from "../interpreter/objects.js"
+import { constructor, constants, type Method, methods } from "../interpreter/native.js"
+import { coerceToNumber, type Value } from "../interpreter/objects.js"
 import { rangeError, typeError } from "../interpreter/model.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
-import { coercion } from "./value.js"
+import { withPrimitives } from "../interpreter/callback.js"
+import { coerce, coercion } from "./value.js"

 export const numberGlobal = <R>(ctx: Interpreter<R>) => {
  const builtins = ctx.builtins
@@ -26,46 +27,36 @@ export const numberGlobal = <R>(ctx: Interpreter<R>) => {
    ["isFinite", 1, (_, args) => Number.isFinite(args[0])],
    ["isNaN", 1, (_, args) => Number.isNaN(args[0])],
    ["isSafeInteger", 1, (_, args) => Number.isSafeInteger(args[0])],
-    [
-      "parseInt",
-      2,
-      (_, args) => {
-        return parseInt(coerceToString(args[0]), coerceToNumber(args[1]))
-      },
-    ],
-    ["parseFloat", 1, (_, args) => parseFloat(coerceToString(args[0]))],
+    ["parseInt", 2, (_, args) => coerce(ctx, "parseInt", args)],
+    ["parseFloat", 1, (_, args) => coerce(ctx, "parseFloat", args)],
  ])

  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 = (arg: Value): number | undefined => (arg === undefined ? undefined : coerceToNumber(arg))
+  // The receiver is checked first, then the one argument converts through ToPrimitive with the number hint.
+  const formatting = (name: string, op: (value: number, digits: number | undefined) => string): Method => [
+    name,
+    1,
+    (thisValue, args) => {
+      const value = self(thisValue, name)
+      return withPrimitives(ctx, "number", [args[0]], ([digits]) =>
+        op(value, digits === undefined ? undefined : coerceToNumber(digits)),
+      )
+    },
+  ]
  methods(builtins, builtins.Number, [
-    ["toFixed", 1, (thisValue, args) => self(thisValue, "toFixed").toFixed(optNum(args[0]))],
+    formatting("toFixed", (value, digits) => value.toFixed(digits)),
    ["toLocaleString", 0, (thisValue) => self(thisValue, "toLocaleString").toLocaleString("en-US")],
-    ["toExponential", 1, (thisValue, args) => self(thisValue, "toExponential").toExponential(optNum(args[0]))],
-    [
-      "toPrecision",
-      1,
-      (thisValue, args) => {
-        const value = self(thisValue, "toPrecision")
-        const digits = optNum(args[0])
-        return digits === undefined ? value.toString() : value.toPrecision(digits)
-      },
-    ],
-    [
-      "toString",
-      1,
-      (thisValue, args) => {
-        const value = self(thisValue, "toString")
-        const radix = optNum(args[0])
-        if (radix !== undefined && (radix < 2 || radix > 36)) {
-          throw rangeError("Number.toString radix must be between 2 and 36.")
-        }
-        return value.toString(radix)
-      },
-    ],
+    formatting("toExponential", (value, digits) => value.toExponential(digits)),
+    formatting("toPrecision", (value, digits) => (digits === undefined ? value.toString() : value.toPrecision(digits))),
+    formatting("toString", (value, radix) => {
+      if (radix !== undefined && (radix < 2 || radix > 36)) {
+        throw rangeError("Number.toString radix must be between 2 and 36.")
+      }
+      return value.toString(radix)
+    }),
    ["valueOf", 0, (thisValue) => self(thisValue, "valueOf")],
  ])
  return number
@@ -17,7 +17,13 @@ import {
  type Value,
 } from "../interpreter/objects.js"
 import { containsOpaqueReference, typeofValue } from "../interpreter/references.js"
-import { applyCollectionCallback, isSupportedCallback, toPrimitiveString } from "../interpreter/callback.js"
+import {
+  applyCollectionCallback,
+  type Hint,
+  isSupportedCallback,
+  toPrimitiveString,
+  withPrimitives,
+} from "../interpreter/callback.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
 import { matchToValue, toHostRegex } from "./regexp.js"
 import { coercion } from "./value.js"
@@ -142,34 +148,72 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
    args[index] === undefined ? undefined : num(name, args, index)
  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<Value>): void => {
-    if (args[0] instanceof RegExpObj) {
-      throw typeError(
-        `String.${name} cannot take a regular expression; use regex.test(string) or String.search instead.`,
-      )
-    }
-  }
+  // ToPrimitive in spec order: the receiver, then the arguments the method consumes, one hint per position; the
+  // rest pass through as they are.
  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)
-      if (typeofValue(args[1]) === "function") {
+    hints: ReadonlyArray<Hint> = [],
+  ): Method => [
+    name,
+    length,
+    (thisValue, args) => {
+      if (thisValue === null || thisValue === undefined) {
+        throw typeError(`String.prototype.${name} called on null or undefined.`)
+      }
+      return withPrimitives(
+        ctx,
+        ["string", ...hints],
+        [thisValue, ...args.slice(0, hints.length)],
+        ([value, ...primitives]) => op(coerceToString(value), [...primitives, ...args.slice(hints.length)]),
+      )
+    },
+  ]
+  // includes, startsWith, and endsWith reject a RegExp before converting their search string and position.
+  const searching = (name: string, op: (value: string, search: string, position: number | undefined) => boolean) =>
+    simple(name, 1, (value, args) => {
+      if (args[0] instanceof RegExpObj) {
        throw typeError(
-          `String.${name} cannot use this callable as a replacer; wrap it in an arrow function, e.g. (match) => tools.ns.tool(match).`,
+          `String.${name} cannot take a regular expression; use regex.test(string) or String.search instead.`,
        )
      }
-      if (args[0] instanceof RegExpObj) {
-        const pattern = args[0].regex
-        const replacement = str(name, args, 1)
-        if (name === "replaceAll") replaceAllNeedsGlobal(pattern)
-        return name === "replace" ? value.replace(pattern, replacement) : value.replaceAll(pattern, replacement)
-      }
-      if (name === "replace") return value.replace(str(name, args, 0), str(name, args, 1))
-      return value.replaceAll(str(name, args, 0), str(name, args, 1))
+      return withPrimitives(ctx, ["string", "number"], args.slice(0, 2), (primitives) =>
+        op(value, str(name, primitives, 0), optNum(name, primitives, 1)),
+      )
+    })
+  // match, matchAll, and search read a RegExp as is and convert anything else to its pattern text.
+  const withPattern = (args: Array<Value>, op: (pattern: Value) => Value) =>
+    args[0] instanceof RegExpObj ? op(args[0]) : withPrimitives(ctx, "string", [args[0]], ([text]) => op(text))
+  const replace = (name: "replace" | "replaceAll") =>
+    simple(name, 2, (value, args) => {
+      const pattern = args[0]
+      const replacer = args[1]
+      // A RegExp pattern is used as is; a plain one converts to its search string, then a non-callable replacement.
+      return withPrimitives(
+        ctx,
+        "string",
+        [pattern instanceof RegExpObj ? undefined : pattern, isSupportedCallback(replacer) ? undefined : replacer],
+        ([search, replacement]) => {
+          if (isSupportedCallback(replacer)) {
+            return replaceWithCallback(ctx, value, name, [pattern instanceof RegExpObj ? pattern : search, replacer])
+          }
+          if (typeofValue(replacer) === "function") {
+            throw typeError(
+              `String.${name} cannot use this callable as a replacer; wrap it in an arrow function, e.g. (match) => tools.ns.tool(match).`,
+            )
+          }
+          const primitives = [search, replacement]
+          if (pattern instanceof RegExpObj) {
+            const regex = pattern.regex
+            const text = str(name, primitives, 1)
+            if (name === "replaceAll") replaceAllNeedsGlobal(regex)
+            return name === "replace" ? value.replace(regex, text) : value.replaceAll(regex, text)
+          }
+          if (name === "replace") return value.replace(str(name, primitives, 0), str(name, primitives, 1))
+          return value.replaceAll(str(name, primitives, 0), str(name, primitives, 1))
+        },
+      )
    })

  methods(builtins, builtins.String, [
@@ -185,107 +229,148 @@ export const stringGlobal = <R>(ctx: Interpreter<R>) => {
    simple("trimEnd", 0, (value) => value.trimEnd()),
    simple("trimRight", 0, (value) => value.trimEnd()),
    // Locale/options are deliberately unsupported; comparison uses the host default locale.
-    simple("localeCompare", 1, (value, args) => value.localeCompare(str("localeCompare", args, 0))),
-    simple("normalize", 0, (value, args) => {
-      const form = optStr("normalize", args, 0)
-      try {
-        return value.normalize(form)
-      } catch {
-        throw rangeError(
-          `String.normalize expects the form "NFC", "NFD", "NFKC", or "NFKD" (got ${JSON.stringify(form)}).`,
-        )
-      }
-    }),
+    simple("localeCompare", 1, (value, args) => value.localeCompare(str("localeCompare", args, 0)), ["string"]),
+    simple(
+      "normalize",
+      0,
+      (value, args) => {
+        const form = optStr("normalize", args, 0)
+        try {
+          return value.normalize(form)
+        } catch {
+          throw rangeError(
+            `String.normalize expects the form "NFC", "NFD", "NFKC", or "NFKD" (got ${JSON.stringify(form)}).`,
+          )
+        }
+      },
+      ["string"],
+    ),
    simple("split", 2, (value, args) => {
-      const wrap = (parts: Array<string>) => new Arr(builtins.Array, parts)
-      // Native: an undefined separator returns the whole string, not a split on "undefined",
-      // unless the limit truncates to zero.
-      const requestedLimit = optNum("split", args, 1)
-      if (args[0] === undefined) {
-        return wrap(requestedLimit !== undefined && requestedLimit >>> 0 === 0 ? [] : [value])
-      }
-      const parts =
-        args[0] instanceof RegExpObj
-          ? value.split(args[0].regex, requestedLimit)
-          : value.split(str("split", args, 0), requestedLimit === undefined ? undefined : requestedLimit >>> 0)
-      checkArrayLength(parts.length)
-      return wrap(parts)
+      const separator = args[0]
+      // A RegExp separator is used as is; the limit converts before a plain separator does, as in the spec.
+      return withPrimitives(
+        ctx,
+        ["number", "string"],
+        [args[1], separator instanceof RegExpObj ? undefined : separator],
+        ([limit, pattern]) => {
+          const wrap = (parts: Array<string>) => new Arr(builtins.Array, parts)
+          // Native: an undefined separator returns the whole string, not a split on "undefined",
+          // unless the limit truncates to zero.
+          const requestedLimit = args[1] === undefined ? undefined : num("split", [pattern, limit], 1)
+          if (separator === undefined) {
+            return wrap(requestedLimit !== undefined && requestedLimit >>> 0 === 0 ? [] : [value])
+          }
+          const parts =
+            separator instanceof RegExpObj
+              ? value.split(separator.regex, requestedLimit)
+              : value.split(str("split", [pattern], 0), requestedLimit === undefined ? undefined : requestedLimit >>> 0)
+          checkArrayLength(parts.length)
+          return wrap(parts)
+        },
+      )
    }),
-    simple("slice", 2, (value, args) => value.slice(optNum("slice", args, 0), optNum("slice", args, 1))),
-    simple("includes", 1, (value, args) => {
-      rejectRegex("includes", args)
-      return value.includes(str("includes", args, 0), optNum("includes", args, 1))
-    }),
-    simple("startsWith", 1, (value, args) => {
-      rejectRegex("startsWith", args)
-      return value.startsWith(str("startsWith", args, 0), optNum("startsWith", args, 1))
-    }),
-    simple("endsWith", 1, (value, args) => {
-      rejectRegex("endsWith", args)
-      return value.endsWith(str("endsWith", args, 0), optNum("endsWith", args, 1))
-    }),
-    simple("indexOf", 1, (value, args) => value.indexOf(str("indexOf", args, 0), optNum("indexOf", args, 1))),
-    simple("lastIndexOf", 1, (value, args) =>
-      value.lastIndexOf(str("lastIndexOf", args, 0), optNum("lastIndexOf", args, 1)),
+    simple("slice", 2, (value, args) => value.slice(optNum("slice", args, 0), optNum("slice", args, 1)), [
+      "number",
+      "number",
+    ]),
+    searching("includes", (value, search, position) => value.includes(search, position)),
+    searching("startsWith", (value, search, position) => value.startsWith(search, position)),
+    searching("endsWith", (value, search, position) => value.endsWith(search, position)),
+    simple("indexOf", 1, (value, args) => value.indexOf(str("indexOf", args, 0), optNum("indexOf", args, 1)), [
+      "string",
+      "number",
+    ]),
+    simple(
+      "lastIndexOf",
+      1,
+      (value, args) => value.lastIndexOf(str("lastIndexOf", args, 0), optNum("lastIndexOf", args, 1)),
+      ["string", "number"],
    ),
    replace("replace"),
    replace("replaceAll"),
-    simple("match", 1, (value, args) => {
-      const pattern = toHostRegex(args[0], "match")
-      const matched = value.match(pattern)
-      if (matched === null) return null
-      // Preserve the own `index` and `groups` properties on non-global matches.
-      if (pattern.global) return new Arr(builtins.Array, [...matched])
-      return matchToValue(builtins, matched)
-    }),
-    simple("matchAll", 1, (value, args) => {
-      const pattern = toHostRegex(args[0], "matchAll", "g")
-      if (!pattern.global) {
-        throw typeError(
-          `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<Value> = []
-      for (const match of value.matchAll(pattern)) {
-        checkArrayLength(matches.length + 1)
-        matches.push(matchToValue(builtins, match))
-      }
-      return new Arr(builtins.Array, matches)
-    }),
-    simple("search", 1, (value, args) => value.search(toHostRegex(args[0], "search"))),
-    simple("repeat", 1, (value, args) => {
-      const count = num("repeat", args, 0)
-      if (!Number.isFinite(count) || count < 0) {
-        throw rangeError("String.repeat expects a finite non-negative count.")
-      }
-      checkStringLength(value.length * count)
-      return value.repeat(count)
-    }),
-    simple("padStart", 1, (value, args) => {
-      const length = num("padStart", args, 0)
-      checkStringLength(length)
-      return value.padStart(length, optStr("padStart", args, 1))
-    }),
-    simple("padEnd", 1, (value, args) => {
-      const length = num("padEnd", args, 0)
-      checkStringLength(length)
-      return value.padEnd(length, optStr("padEnd", args, 1))
-    }),
-    simple("charAt", 1, (value, args) => value.charAt(optNum("charAt", args, 0) ?? 0)),
-    simple("at", 1, (value, args) => value.at(optNum("at", args, 0) ?? 0)),
-    simple("substring", 2, (value, args) =>
-      value.substring(optNum("substring", args, 0) ?? 0, optNum("substring", args, 1)),
+    simple("match", 1, (value, args) =>
+      withPattern(args, (arg) => {
+        const regex = toHostRegex(arg, "match")
+        const matched = value.match(regex)
+        if (matched === null) return null
+        // Preserve the own `index` and `groups` properties on non-global matches.
+        if (regex.global) return new Arr(builtins.Array, [...matched])
+        return matchToValue(builtins, matched)
+      }),
    ),
-    simple("substr", 2, (value, args) => value.substr(optNum("substr", args, 0) ?? 0, optNum("substr", args, 1))),
+    simple("matchAll", 1, (value, args) =>
+      withPattern(args, (arg) => {
+        const regex = toHostRegex(arg, "matchAll", "g")
+        if (!regex.global) {
+          throw typeError(
+            `String.matchAll requires a regular expression with the global (g) flag: write /${regex.source}/${regex.flags}g, or use String.match for a single match.`,
+          )
+        }
+        const matches: Array<Value> = []
+        for (const match of value.matchAll(regex)) {
+          checkArrayLength(matches.length + 1)
+          matches.push(matchToValue(builtins, match))
+        }
+        return new Arr(builtins.Array, matches)
+      }),
+    ),
+    simple("search", 1, (value, args) => withPattern(args, (arg) => value.search(toHostRegex(arg, "search")))),
+    simple(
+      "repeat",
+      1,
+      (value, args) => {
+        const count = num("repeat", args, 0)
+        if (!Number.isFinite(count) || count < 0) {
+          throw rangeError("String.repeat expects a finite non-negative count.")
+        }
+        checkStringLength(value.length * count)
+        return value.repeat(count)
+      },
+      ["number"],
+    ),
+    simple(
+      "padStart",
+      1,
+      (value, args) => {
+        const length = num("padStart", args, 0)
+        checkStringLength(length)
+        return value.padStart(length, optStr("padStart", args, 1))
+      },
+      ["number", "string"],
+    ),
+    simple(
+      "padEnd",
+      1,
+      (value, args) => {
+        const length = num("padEnd", args, 0)
+        checkStringLength(length)
+        return value.padEnd(length, optStr("padEnd", args, 1))
+      },
+      ["number", "string"],
+    ),
+    simple("charAt", 1, (value, args) => value.charAt(optNum("charAt", args, 0) ?? 0), ["number"]),
+    simple("at", 1, (value, args) => value.at(optNum("at", args, 0) ?? 0), ["number"]),
+    simple(
+      "substring",
+      2,
+      (value, args) => value.substring(optNum("substring", args, 0) ?? 0, optNum("substring", args, 1)),
+      ["number", "number"],
+    ),
+    simple("substr", 2, (value, args) => value.substr(optNum("substr", args, 0) ?? 0, optNum("substr", args, 1)), [
+      "number",
+      "number",
+    ]),
    simple("isWellFormed", 0, (value) => value.isWellFormed()),
    simple("toWellFormed", 0, (value) => value.toWellFormed()),
-    simple("charCodeAt", 1, (value, args) => value.charCodeAt(optNum("charCodeAt", args, 0) ?? 0)),
-    simple("codePointAt", 1, (value, args) => value.codePointAt(optNum("codePointAt", args, 0) ?? 0)),
-    simple("concat", 1, (value, args) => {
-      const joined = value.concat(...args.map((_, index) => str("concat", args, index)))
-      checkStringLength(joined.length)
-      return joined
-    }),
+    simple("charCodeAt", 1, (value, args) => value.charCodeAt(optNum("charCodeAt", args, 0) ?? 0), ["number"]),
+    simple("codePointAt", 1, (value, args) => value.codePointAt(optNum("codePointAt", args, 0) ?? 0), ["number"]),
+    simple("concat", 1, (value, args) =>
+      withPrimitives(ctx, "string", args, (parts) => {
+        const joined = value.concat(...parts.map((_, index) => str("concat", parts, index)))
+        checkStringLength(joined.length)
+        return joined
+      }),
+    ),
  ])
  define(
    builtins.String,
@@ -281,7 +281,7 @@ export const urlSearchParamsGlobal = <R>(ctx: Interpreter<R>) => {
        const target = self(thisValue, "forEach")
        const apply = applyCollectionCallback(ctx, args[0], "URLSearchParams.forEach")
        return Effect.gen(function* () {
-          for (const [key, value] of Array.from(target.params.entries())) yield* apply([value, key, target])
+          for (const [key, value] of Array.from(target.params.entries())) yield* apply([value, key, target], args[1])
          return undefined
        })
      },
@@ -1,12 +1,13 @@
 import { fn } from "../interpreter/native.js"
 import { coerceToNumber, coerceToString, type Native, type Value } from "../interpreter/objects.js"
 import type { Interpreter } from "../interpreter/interpreter.js"
+import { withPrimitives } from "../interpreter/callback.js"

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

 export type Coercion = "Number" | "String" | "Boolean" | "parseInt" | "parseFloat" | "isFinite" | "isNaN"

-const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<Value>): Value => {
+export const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<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) {
@@ -14,15 +15,19 @@ const coerce = <R>(ctx: Interpreter<R>, name: Coercion, args: Array<Value>): Val
    if (name === "String") return ""
  }
  const raw = args[0]
-  if (name === "Number") return coerceToNumber(raw)
  if (name === "Boolean") return Boolean(raw)
-  if (name === "isFinite") return Number.isFinite(coerceToNumber(raw))
-  if (name === "isNaN") return Number.isNaN(coerceToNumber(raw))
  if (name === "parseInt") {
-    return parseInt(coerceToString(raw), coerceToNumber(args[1]))
+    return withPrimitives(ctx, ["string", "number"], [raw, args[1]], ([text, radix]) =>
+      parseInt(coerceToString(text), coerceToNumber(radix)),
+    )
  }
-  if (name === "parseFloat") return parseFloat(coerceToString(raw))
-  return coerceToString(raw)
+  return withPrimitives(ctx, name === "String" || name === "parseFloat" ? "string" : "number", [raw], ([value]) => {
+    if (name === "Number") return coerceToNumber(value)
+    if (name === "isFinite") return Number.isFinite(coerceToNumber(value))
+    if (name === "isNaN") return Number.isNaN(coerceToNumber(value))
+    if (name === "parseFloat") return parseFloat(coerceToString(value))
+    return coerceToString(value)
+  })
 }

 /** A global coercion function such as `Number` or `parseInt`. */
@@ -16,6 +16,8 @@ import {
  Obj,
  RegExpObj,
  SetObj,
+  WeakMapObj,
+  WeakSetObj,
  coerceToString,
  type Value,
 } from "../interpreter/objects.js"
@@ -84,7 +86,9 @@ export const structuredCloneGlobal = <R>(ctx: Interpreter<R>) =>
        if (hasOwn(value, "cause")) define(copy, "cause", clone(getOwn(value, "cause")), hidden)
        return copy
      }
-      if (isRuntimeReference(value)) throw typeError(`DataCloneError: ${describeValue(value)} could not be cloned.`)
+      if (isRuntimeReference(value) || value instanceof WeakMapObj || value instanceof WeakSetObj) {
+        throw typeError(`DataCloneError: ${describeValue(value)} could not be cloned.`)
+      }
      const copy = remember(
        value instanceof Arr ? new Arr(builtins.Array, new Array(value.items.length)) : new Obj(builtins.Object),
      )
@@ -1571,3 +1571,416 @@ describe("this, arguments, and Function.prototype.call/apply/bind", () => {
    )
  })
 })
+
+describe("ToPrimitive: operators and conversions honor program valueOf and toString", () => {
+  test("program-installed valueOf and toString on opaque values are ignored at every site", async () => {
+    expect(
+      await value(`
+        const f = () => 1
+        f.toString = () => "custom"
+        f.valueOf = () => 5
+        return [String(f), \`\${f}\`, [f].join(), new Error(f).message, isNaN(Number(f)), isNaN(Math.abs(f))]
+      `),
+    ).toEqual(["[object Function]", "[object Function]", "[object Function]", "[object Function]", true, true])
+  })
+
+  test("== converts an object facing a non-nullish primitive through its own valueOf", async () => {
+    expect(
+      await value(`
+        const one = { valueOf() { return 1 } }
+        return [one == 1, 1 == one, one == true, one == "1", one == null, one == one, one == { valueOf() { return 1 } }, [1] == 1]
+      `),
+    ).toEqual([true, true, true, true, false, true, false, true])
+    expect((await error(`(() => 1) == 1`)).message).toContain("Binary operators require data values")
+  })
+
+  test("operators, unary, template literals, and conversion functions use the object's own methods", async () => {
+    expect(
+      await value(`
+        const money = { valueOf() { return 7 } }
+        return [money * 2, money + 1, money + "", -money, +money, ~money, money < 8, money ** 2, money | 8,
+          Number(money), Math.max(money, 1), \`\${money}\`, String(money), isNaN(money), isFinite(money),
+          parseInt({ toString() { return "42px" } }), parseInt("ff", { valueOf() { return 16 } }),
+          Number.parseFloat({ toString() { return "1.5" } })]
+      `),
+    ).toEqual([
+      14,
+      8,
+      "7",
+      -7,
+      7,
+      -8,
+      true,
+      49,
+      15,
+      7,
+      7,
+      "[object Object]",
+      "[object Object]",
+      false,
+      true,
+      42,
+      255,
+      1.5,
+    ])
+  })
+
+  test("the hint picks the method: + and Number prefer valueOf, template literals and String prefer toString", async () => {
+    expect(
+      await value(`
+        const both = { valueOf() { return 1 }, toString() { return "s" } }
+        return [both + "", \`\${both}\`, String(both), both * 2, new Error(both).message, [both].join(), [both, 2] + ""]
+      `),
+    ).toEqual(["1", "s", "s", 2, "s", "s", "s,2"])
+  })
+
+  test("operands convert left then right, and a throwing valueOf surfaces as the program error", async () => {
+    expect(
+      await value(`
+        const order = []
+        const a = { valueOf() { order.push("a"); return 1 } }, b = { valueOf() { order.push("b"); return 2 } }
+        a + b; a < b; a - b
+        return order
+      `),
+    ).toEqual(["a", "b", "a", "b", "a", "b"])
+    expect(
+      await value(`
+        const bad = { valueOf() { throw new RangeError("nope") } }
+        const names = []
+        try { bad + 1 } catch (e) { names.push(e.name) }
+        try { Number(bad) } catch (e) { names.push(e.name) }
+        try { Math.abs(bad) } catch (e) { names.push(e.name) }
+        return names
+      `),
+    ).toEqual(["RangeError", "RangeError", "RangeError"])
+  })
+
+  test("arrays keep their built-in join form unless the program replaces toString", async () => {
+    expect(
+      await value(`
+        const arr = [1, 2]
+        const before = [arr + "", [] + [], [1, , 3].join("-"), [1, { toString() { return "q" } }].join("-")]
+        arr.toString = () => "x"
+        return [...before, arr + "", \`\${arr}\`, String(arr)]
+      `),
+    ).toEqual(["1,2", "", "1--3", "1-q", "x", "x", "x"])
+  })
+
+  test("update and compound assignment convert the current value", async () => {
+    expect(
+      await value(`
+        let x = { valueOf() { return 5 } }
+        const o = { n: { valueOf() { return 4 } } }
+        const after = x++
+        o.n += 1
+        o.n++
+        let s = { valueOf() { return 2 } }
+        s *= 3
+        return [after, x, o.n, s]
+      `),
+    ).toEqual([5, 6, 6, 6])
+  })
+
+  test("functions and other opaque values still reject arithmetic, and an object without a primitive form throws", async () => {
+    expect((await error(`const f = () => 1; return f + 1`)).message).toContain("Binary operators require data values")
+    expect((await error(`return -(() => 1)`)).message).toContain("Unary operators require data values")
+    const failure = await error(`return { valueOf() { return {} }, toString() { return [] } } + 1`)
+    expect(failure.message).toContain("Cannot convert object to primitive value")
+  })
+})
+
+describe("object destructuring from primitives", () => {
+  test("reads through the primitive's prototype like member access", async () => {
+    expect(
+      await value(`
+        const { length, 0: first, toUpperCase } = "abc"
+        const { toFixed } = 1.5
+        const {} = true
+        const { 0: a, ...rest } = "xyz"
+        const { ...none } = 42
+        let n
+        ;({ length: n } = "hello")
+        return [length, first, toUpperCase.call("q"), toFixed.call(2.345, 1), a, rest, none, n]
+      `),
+    ).toEqual([3, "a", "Q", "2.3", "x", { 1: "y", 2: "z" }, {}, 5])
+  })
+
+  test("only null and undefined sources throw", async () => {
+    expect((await error(`const { a } = null`)).message).toContain("Cannot destructure null as it is null")
+    expect((await error(`const {} = undefined`)).message).toContain("Cannot destructure undefined")
+    expect((await error(`let a; ({ a } = undefined)`)).message).toContain("Cannot destructure undefined")
+  })
+})
+
+describe("Date components convert through ToPrimitive", () => {
+  test("construction and Date.UTC ask each of the first seven arguments in order", async () => {
+    expect(
+      await value(`
+        const seen = []
+        const part = (n) => ({ valueOf() { seen.push(n); return n } })
+        const time = new Date(part(2024), part(1), part(2), part(3), part(4), part(5), part(6), part(99)).getTime()
+        const utc = Date.UTC(2024, { valueOf() { return 0 } }, 15)
+        return [seen, time === new Date(2024, 1, 2, 3, 4, 5, 6).getTime(), utc === Date.UTC(2024, 0, 15)]
+      `),
+    ).toEqual([[2024, 1, 2, 3, 4, 5, 6], true, true])
+    expect((await error(`new Date(2024, { valueOf() { throw new RangeError("boom") } })`)).message).toContain("boom")
+  })
+
+  test("setters on an invalid Date answer NaN without overwriting a time set during coercion", async () => {
+    expect(
+      await value(`
+        const d = new Date(NaN)
+        const result = d.setDate({ valueOf() { d.setTime(0); return 1 } })
+        const y = new Date(NaN)
+        return [Number.isNaN(result), d.getTime(), y.setFullYear(2020) === Date.UTC(2020, 0, 1) - y.getTimezoneOffset() * 60000]
+      `),
+    ).toEqual([true, 0, true])
+  })
+})
+
+describe("iteration callbacks receive thisArg", () => {
+  test("Array, Array.from, Map, Set, URLSearchParams, Headers, and Uint8Array pass it as this", async () => {
+    expect(
+      await value(`
+        const c = { n: 0 }
+        const count = function () { this.n++ }
+        ;[1, 2].forEach(count, c)
+        ;[1].map(count, c)
+        ;[1].filter(count, c)
+        ;[1].find(count, c)
+        ;[1].findIndex(count, c)
+        ;[1].findLast(count, c)
+        ;[1].findLastIndex(count, c)
+        ;[1].some(count, c)
+        ;[1].every(count, c)
+        ;[1].flatMap(count, c)
+        Array.from([1], count, c)
+        Array.from({ length: 1 }, count, c)
+        new Map([[1, 1]]).forEach(count, c)
+        new Set([1]).forEach(count, c)
+        new URLSearchParams("a=1").forEach(count, c)
+        new Headers({ a: "1" }).forEach(count, c)
+        new Uint8Array([1]).forEach(count, c)
+        return c.n
+      `),
+    ).toBe(18)
+    expect(await value(`return [1, 2].map(function (x) { return x + this.v }, { v: 10 })`)).toEqual([11, 12])
+  })
+
+  test("arrows keep their lexical this, reduce takes an initial value instead, and opaque values are only bound", async () => {
+    expect(await value(`return [1].map(() => typeof this, { v: 1 })`)).toEqual(["undefined"])
+    expect(
+      await value(`return [1, 2].reduce(function (a, b) { return a + b + (this === undefined ? 0 : 100) }, 0)`),
+    ).toBe(3)
+    expect(
+      await value(`
+        let seen
+        ;[1].forEach(function () { seen = this }, tools.nowhere)
+        return typeof seen
+      `),
+    ).toBe("function")
+  })
+})
+
+describe("computed property keys convert through the object's own toString", () => {
+  test("reads, writes, compound assignment, in, delete, literals, and destructuring share one conversion", async () => {
+    expect(
+      await value(`
+        const key = { toString() { return "id" } }
+        const o = {}
+        o[key] = 1
+        o[key] += 1
+        const literal = { [key]: "lit" }
+        const had = key in o
+        delete literal[key]
+        return [o.id, had, (({ [key]: v }) => v)(o), literal, o[[1, 2]] === undefined]
+      `),
+    ).toEqual([2, true, 2, {}, true])
+    expect(
+      await value(`
+        const seen = []
+        const base = { x: 1 }
+        base[{ toString() { seen.push(1); return "" } }] ^= 0
+        base[{ toString() { seen.push(2); return "x" } }]++
+        return [seen, base[""], base.x]
+      `),
+    ).toEqual([[1, 2], 0, 2])
+  })
+
+  test("valueOf is the fallback, a symbol result stays a symbol, and conversion failures surface", async () => {
+    expect(
+      await value(`
+        const o = { 7: "seven" }
+        const sym = { toString() { return Symbol.iterator } }
+        o[sym] = 1
+        return [o[{ valueOf() { return 7 }, toString: undefined }], typeof o[Symbol.iterator], Object.keys(o)]
+      `),
+    ).toEqual(["seven", "number", ["7"]])
+    expect((await error(`({})[{ toString() { throw new RangeError("bad key") } }]`)).message).toContain("bad key")
+    expect((await error(`({})[{ toString() { return {} }, valueOf() { return {} } }]`)).message).toContain(
+      "Cannot convert object to primitive value",
+    )
+    expect((await error(`const key = { toString() { return "a" } }; key in 5`)).message).toContain(
+      "requires a data object on the right-hand side",
+    )
+  })
+
+  test("a nullish base throws before the key converts, as ToObject precedes ToPropertyKey", async () => {
+    const failure = await error(`const base = null; base[{ toString() { throw new RangeError("key evaluated") } }]`)
+    expect(failure.message).toContain("Cannot read properties of null")
+  })
+
+  test("opaque values keep their built-in key form and a tool reference toString is never called", async () => {
+    expect(
+      await value(`
+        const o = { "[object Function]": 1, "[object Promise]": 2 }
+        return [o[() => 1], o[Promise.resolve("k")]]
+      `),
+    ).toEqual([1, 2])
+    expect((await error(`({})[{ toString: tools.nowhere }] = 1`)).message).toContain(
+      "Cannot convert object to primitive value",
+    )
+  })
+})
+
+describe("String and Number method arguments convert through ToPrimitive", () => {
+  test("string positions use the string hint and numeric positions the number hint", async () => {
+    expect(
+      await value(`
+        const s = { toString() { return "b" } }
+        const n = { valueOf() { return 1 } }
+        return [
+          "abc".indexOf(s), "abc".lastIndexOf(s), "abc".includes(s), "abc".startsWith(s, n), "abc".endsWith(s, 2),
+          "abc".charAt(n), "abc".at({ valueOf() { return -1 } }), "abc".slice(n), "abc".substring(n, 2),
+          "abc".charCodeAt(n), "a".padStart({ valueOf() { return 3 } }, s), "x".padEnd(3, s), "ab".repeat({ valueOf() { return 2 } }),
+          "a".concat(s, { valueOf() { return 1 }, toString() { return "T" } }), "b".localeCompare(s),
+          (1.005).toFixed({ valueOf() { return 2 } }), (255).toString({ valueOf() { return 16 } }),
+          (1234.5678).toPrecision({ valueOf() { return 6 } }), (12345).toExponential({ valueOf() { return 2 } }),
+        ]
+      `),
+    ).toEqual([
+      1,
+      1,
+      true,
+      true,
+      true,
+      "b",
+      "c",
+      "bc",
+      "b",
+      98,
+      "bba",
+      "xbb",
+      "abab",
+      "abT",
+      0,
+      "1.00",
+      "ff",
+      "1234.57",
+      "1.23e+4",
+    ])
+  })
+
+  test("split, replace, match, and search convert a plain pattern but keep a RegExp as is", async () => {
+    expect(
+      await value(`
+        const s = { toString() { return "b" } }
+        return [
+          "abc".split(s), "abc".split(/b/, { valueOf() { return 1 } }), "abc".split(undefined, { valueOf() { return undefined } }),
+          "abc".replace(s, "X"), "abc".replace(/b/, { toString() { return "R" } }), "abc".replaceAll(s, s),
+          "abc".replace(s, (m) => m.toUpperCase()), "abc".match(s)[0], "abcb".matchAll(s).length, "abc".search(s),
+        ]
+      `),
+    ).toEqual([["a", "c"], ["a"], [], "aXc", "aRc", "abc", "aBc", "b", 2, 1])
+    expect((await error(`"abc".includes(/b/)`)).message).toContain("cannot take a regular expression")
+  })
+
+  test("the receiver converts first, then each consumed argument, in spec order; extra arguments are untouched", async () => {
+    expect(
+      await value(`
+        const log = []
+        const observer = (name, string, number) => ({
+          toString() { log.push("toString:" + name); return string },
+          valueOf() { log.push("valueOf:" + name); return number },
+        })
+        const padded = String.prototype.padStart.call(observer("receiver", {}, "abc"), observer("maxLength", 11, {}), observer("fillString", {}, "def"))
+        const extra = "abc".indexOf("b", 1, { valueOf() { throw new Error("extra argument converted") } })
+        return [padded, log, extra, String.prototype.trim.call({ toString() { return " abc " } })]
+      `),
+    ).toEqual([
+      "defdefdeabc",
+      [
+        "toString:receiver",
+        "valueOf:receiver",
+        "valueOf:maxLength",
+        "toString:maxLength",
+        "toString:fillString",
+        "valueOf:fillString",
+      ],
+      1,
+      "abc",
+    ])
+  })
+
+  test("conversion failures surface and opaque arguments still reject", async () => {
+    expect((await error(`"abc".indexOf({ toString() { throw new RangeError("intostr") } })`)).message).toContain(
+      "intostr",
+    )
+    expect((await error(`(1).toString({ valueOf() { throw new SyntaxError("poison") } })`)).message).toContain("poison")
+    expect((await error(`(1).toFixed({ toString() { return {} }, valueOf() { return {} } })`)).message).toContain(
+      "Cannot convert object to primitive value",
+    )
+    expect((await error(`"abc".indexOf(tools.nowhere)`)).message).toContain("expects argument 1 to be a data value")
+    expect((await error(`"abc".indexOf(Promise.resolve("b"))`)).message).toContain(
+      "expects argument 1 to be a data value",
+    )
+  })
+})
+
+describe("WeakMap and WeakSet", () => {
+  test("hold program objects by identity and answer like JS for non-object keys", async () => {
+    expect(
+      await value(`
+        const k = {}
+        const f = () => 1
+        const wm = new WeakMap([[k, 1]])
+        const ws = new WeakSet([k])
+        return [
+          wm.set(f, "fn") === wm, wm.get(k), wm.get(f), wm.has({}), wm.get(1), wm.has(1), wm.delete("s"),
+          wm.getOrInsert(k, 9), wm.getOrInsertComputed({}, (key) => typeof key),
+          ws.add(f) === ws, ws.has(k), ws.has(f), ws.has(1), ws.delete(k), ws.has(k),
+          String(wm), wm.size, "clear" in wm, Symbol.iterator in ws, JSON.stringify(wm),
+        ]
+      `),
+    ).toEqual([
+      true,
+      1,
+      "fn",
+      false,
+      null,
+      false,
+      false,
+      1,
+      "object",
+      true,
+      true,
+      true,
+      false,
+      true,
+      false,
+      "[object WeakMap]",
+      null,
+      false,
+      false,
+      "{}",
+    ])
+  })
+
+  test("reject primitive keys, plain calls, bad receivers, and cloning", async () => {
+    expect((await error(`new WeakMap().set(1, 1)`)).message).toContain("Invalid value used as weak map key")
+    expect((await error(`new WeakSet([1])`)).message).toContain("Invalid value used in weak set")
+    expect((await error(`WeakMap()`)).message).toContain("new")
+    expect((await error(`WeakMap.prototype.get.call(new Map(), {})`)).message).toContain("incompatible receiver")
+    expect((await error(`structuredClone(new WeakSet())`)).message).toContain("DataCloneError")
+  })
+})
@@ -12,7 +12,8 @@ Without them the runner registers no tests, so CI is unaffected. Licensed under

 ## Layout

- `manifest.json` — the pinned upstream revision, which upstream directories are copied, and what is left out.
+- `manifest.json` — the pinned upstream revision, which upstream directories are copied (every `built-ins` and
+  `language` directory, about 14,900 files after filtering), and what is left out.
 - `built-ins/`, `language/` — the copied files, mirroring upstream `test/`; gitignored.
 - `skipped.txt` — vendored files that fail on a known interpreter gap, one `path  # reason` per line. They are
  skipped, and each gap is listed as unchecked in `interpreter-support.md`.
@@ -26,7 +27,8 @@ Without them the runner registers no tests, so CI is unaffected. Licensed under
 manifest marks unsupported, or when its code matches one of the manifest's `boundaries` patterns. The sync checks the
 checkout is at the pinned revision, so every machine runs the same files. Boundaries are
 intentional limits of the interpreter, not compatibility work: classes, prototype objects, property descriptors,
-accessors, boxed primitives, sloppy mode, `eval`, `Symbol()`, and the `$262` host API. If one
+accessors, boxed primitives, typed arrays and buffers, `WeakRef` and `FinalizationRegistry`, `Reflect` and `Proxy`, sloppy mode, `eval`,
+`Symbol()`, and the `$262` host API. If one
 of those decisions changes, delete its entry and re-sync; the tests are upstream, not lost.

 ## Commands
@@ -1,33 +1,16 @@
 {
  "revision": "250f204f23a9249ff204be2baec29600faae7b75",
-  "directories": [
-    "built-ins/Array/prototype",
-    "built-ins/Function/prototype/apply",
-    "built-ins/Function/prototype/bind",
-    "built-ins/Function/prototype/call",
-    "built-ins/Iterator",
-    "built-ins/Object/freeze",
-    "built-ins/Object/getPrototypeOf",
-    "built-ins/Object/is",
-    "built-ins/Object/isExtensible",
-    "built-ins/Object/isFrozen",
-    "built-ins/Object/isSealed",
-    "built-ins/Object/preventExtensions",
-    "built-ins/String/raw",
-    "language/arguments-object",
-    "language/expressions/does-not-equals",
-    "language/expressions/equals",
-    "language/expressions/tagged-template",
-    "language/expressions/this",
-    "language/statements"
-  ],
+  "directories": ["built-ins", "language"],
  "harness": ["assert.js", "sta.js", "compareArray.js", "doneprintHandle.js"],
  "flags": ["module", "raw", "noStrict"],
  "boundaries": {
    "class": "\\bclass\\s*[A-Za-z_${]",
    "accessor properties": "\\b(get|set)\\s+[\\w$\\[][^\\n(]*\\(",
    "property descriptors": "Object\\.(defineProperty|defineProperties|getOwnPropertyDescriptors?|getOwnPropertyNames|setPrototypeOf)\\b",
-    "boxed primitives": "\\bnew\\s+(String|Number|Boolean)\\s*\\(",
+    "boxed primitives": "\\b(new\\s+(String|Number|Boolean)\\b|Object\\s*\\(\\s*(true|false|-?\\d|['\"]))",
+    "typed arrays and buffers": "\\b(ArrayBuffer|SharedArrayBuffer|DataView|Int8Array|Uint8ClampedArray|Int16Array|Uint16Array|Int32Array|Uint32Array|Float16Array|Float32Array|Float64Array|BigInt64Array|BigUint64Array)\\b",
+    "weak collections": "\\b(WeakRef|FinalizationRegistry)\\b",
+    "Reflect and Proxy": "\\b(Reflect|Proxy)\\b",
    "sloppy mode": "\\bwith\\s*\\(",
    "eval": "\\b(eval|Function)\\b",
    "new.target": "\\bnew\\.target\\b",
@@ -91,8 +74,6 @@
    "Uint16Array",
    "Uint32Array",
    "uint8array-base64",
-    "WeakMap",
-    "WeakSet",
    "WeakRef",
    "FinalizationRegistry",
    "Intl-enumeration",
@@ -354,3 +354,17 @@ describe("tools.search alias", () => {
    expect(await value(runtime, `return await tools.search({})`)).toBe("custom")
  })
 })
+
+describe("tool references under ==", () => {
+  test("compare by identity against data objects without converting them", async () => {
+    const runtime = CodeMode.make({ tools: { probe: echo("Probe", "ok") } })
+    expect(
+      await value(
+        runtime,
+        `let calls = 0
+         const o = { valueOf() { calls++; return 1 } }
+         return [o == tools.probe, tools == { a: 1 }, tools.probe == null, calls]`,
+      ),
+    ).toEqual([false, false, false, 0])
+  })
+})
@@ -361,6 +361,12 @@ export function createBrowserPage(
      visible = value
      updateVisibility()
    },
+    // Freezes the shown page so the renderer can paint it under DOM overlays while the view hides.
+    async capture() {
+      if (closed || !visible || !content) return
+      const image = await contents.capturePage()
+      return image.isEmpty() ? undefined : new Uint8Array(image.toJPEG(90))
+    },
    async execute(command: Browser.Command, signal: AbortSignal): Promise<Browser.Result> {
      await ready
      abortError(signal)
@@ -288,6 +288,9 @@ export function createBrowserPane(storage: StateStore) {
      page.layout(bounds, value.background, value.radius)
      page.setVisible(true)
    },
+    async capture(win: BrowserWindow, bindingID: string, tabID: Browser.TabID) {
+      return (await owned(win, bindingID).pages.get(tabID)?.capture()) ?? null
+    },
    async command(win: BrowserWindow, bindingID: string, command: BrowserPaneCommand) {
      const entry = owned(win, bindingID)
      await execute(entry, { action: command, files: [] }, new AbortController().signal)
@@ -6,7 +6,7 @@ import { IpcPortHandoff } from "../ipc-transport"
 import { Shutdown } from "../lifecycle/shutdown"
 import { isRendererUrl } from "../windows/scheme"
 import { DesktopStorage } from "../storage"
-import { sender } from "./context"
+import { sender, type RpcContext } from "./context"

 export const eventHandlers = EventRpcs.toLayer(
  Effect.gen(function* () {
@@ -25,21 +25,29 @@ export const eventHandlers = EventRpcs.toLayer(
    })
    const remove = yield* shutdown.add(stop)
    yield* Effect.addFinalizer(() => Effect.sync(remove).pipe(Effect.andThen(stop)))
+    const owner = async (context: RpcContext) => {
+      const contents = sender(handoff, context)
+      const win = BrowserWindow.fromWebContents(contents)
+      if (!win || win.isDestroyed() || win.webContents !== contents || !isRendererUrl(contents.getURL())) {
+        throw new Error("browser.pane.owner.invalid")
+      }
+      browser ??= load()
+      return { win, pane: await browser }
+    }
    return EventRpcs.of({
      DesktopEvents: (_request, context) => ipcEventStream(sender(handoff, context).id),
      BrowserPane: ({ request }, context) =>
        Effect.tryPromise(async () => {
-          const contents = sender(handoff, context)
-          const win = BrowserWindow.fromWebContents(contents)
-          if (!win || win.isDestroyed() || win.webContents !== contents || !isRendererUrl(contents.getURL())) {
-            throw new Error("browser.pane.owner.invalid")
-          }
-          browser ??= load()
-          const pane = await browser
-          if (request.type === "register") return pane.register(win, request.bindingID, request.target)
-          if (request.type === "layout") return pane.layout(win, request.bindingID, request.layout)
-          if (request.type === "command") return pane.command(win, request.bindingID, request.command)
-          return pane.close(win, request.bindingID)
+          const target = await owner(context)
+          if (request.type === "register") return target.pane.register(target.win, request.bindingID, request.target)
+          if (request.type === "layout") return target.pane.layout(target.win, request.bindingID, request.layout)
+          if (request.type === "command") return target.pane.command(target.win, request.bindingID, request.command)
+          return target.pane.close(target.win, request.bindingID)
+        }).pipe(Effect.orDie),
+      BrowserPaneCapture: (request, context) =>
+        Effect.tryPromise(async () => {
+          const target = await owner(context)
+          return target.pane.capture(target.win, request.bindingID, request.tabID)
        }).pipe(Effect.orDie),
    })
  }),
@@ -4,6 +4,7 @@ import type { DesktopNativeBundle } from "@opencode/app/i18n/desktop-native"
 import type { UpdaterState } from "@opencode/app/updater"
 import type { WslServersPlatform } from "@opencode/app/wsl/types"
 import type { SshPlatform } from "@opencode/app/ssh"
+import type { Browser } from "@opencode/plugin-browser/rpc"
 import type { BrowserPaneRequest } from "../shared/ipc-rpc/browser"
 import type { WindowBootstrap } from "../shared/window-bootstrap"
 import type {
@@ -31,6 +32,7 @@ export type ElectronAPI = {
  browserPane: {
    request(request: BrowserPaneRequest): Promise<void>
    send(request: BrowserPaneRequest): void
+    capture(bindingID: string, tabID: Browser.TabID): Promise<ArrayBuffer | null>
    onEvent(callback: (value: { readonly bindingID: string; readonly event: BrowserPaneEvent }) => void): () => void
  }
  wslServers: WslServersAPI
@@ -50,6 +50,8 @@ export const api: ElectronAPI = {
  browserPane: {
    request: (request) => invoke("BrowserPane", { request }),
    send: (request) => send("BrowserPane", { request }),
+    capture: (bindingID, tabID) =>
+      invoke("BrowserPaneCapture", { bindingID, tabID }).then((data) => (data ? toArrayBuffer(data) : null)),
    onEvent: (callback) => listen("BrowserPaneEvent", (value) => callback(value)),
  },
  wslServers: {
@@ -46,6 +46,10 @@ export function createDesktopPlatform(
                .catch(() => undefined)
          },
          command: (command) => ready.then(() => api.browserPane.request({ type: "command", bindingID, command })),
+          capture: (tabID) =>
+            ready
+              .then(() => api.browserPane.capture(bindingID, tabID))
+              .then((data) => data && new Blob([data], { type: "image/jpeg" })),
          close() {
            if (closed) return
            closed = true
@@ -1,6 +1,7 @@
 import { Browser } from "@opencode/plugin-browser/rpc"
 import { Schema } from "effect"
 import { Rpc } from "effect/unstable/rpc"
+import { Transferable } from "effect/unstable/workers"

 const text = (maximum: number) => Schema.String.check(Schema.isMinLength(1), Schema.isMaxLength(maximum))
 const bindingID = text(128)
@@ -42,3 +43,7 @@ export const BrowserPaneEventSchema = Schema.Union([
  }),
 ])
 export const BrowserPaneRpc = Rpc.make("BrowserPane", { payload: { request: BrowserPaneRequestSchema } })
+export const BrowserPaneCaptureRpc = Rpc.make("BrowserPaneCapture", {
+  payload: { bindingID, tabID: Browser.TabID },
+  success: Schema.NullOr(Transferable.Uint8Array),
+})
@@ -1,6 +1,6 @@
 import { Schema } from "effect"
 import { Rpc, RpcGroup } from "effect/unstable/rpc"
-import { BrowserPaneEventSchema, BrowserPaneRpc } from "./browser"
+import { BrowserPaneCaptureRpc, BrowserPaneEventSchema, BrowserPaneRpc } from "./browser"
 import { UpdaterStateSchema } from "./updater"
 import { WslServersEventSchema } from "./wsl"
 import { SshState } from "@opencode/app/ssh"
@@ -63,4 +63,4 @@ export const DesktopEvent = Schema.Union([
 export type DesktopEvent = Schema.Schema.Type<typeof DesktopEvent>

 export const DesktopEvents = Rpc.make("DesktopEvents", { success: DesktopEvent, stream: true })
-export const EventRpcs = RpcGroup.make(DesktopEvents, BrowserPaneRpc)
+export const EventRpcs = RpcGroup.make(DesktopEvents, BrowserPaneRpc, BrowserPaneCaptureRpc)
@@ -71,6 +71,10 @@ async function main() {
            void ready.then(() => pane.layout(win, bindingID, layout))
          },
          command: (command) => ready.then(() => pane.command(win, bindingID, command)),
+          capture: (tabID) =>
+            ready
+              .then(() => pane.capture(win, bindingID, tabID))
+              .then((data) => data && new Blob([data], { type: "image/jpeg" })),
          close: () => {
            listeners.delete(bindingID)
            void ready.then(() => pane.close(win, bindingID)).catch(() => {})
@@ -333,6 +333,11 @@ async function main() {
    await call("tabs.focus", { tabID: second.id })
    pane.layout(win, "suite", { tabID: second.id, visible: true, bounds: { x: 0, y: 0, width: 1000, height: 700 } })
    const snap = await call("snapshot", { tabID, boxes: true })
+    const still = await until(() => pane.capture(win, "suite", second.id))
+    assert(still)
+    assert.deepEqual(Array.from(still.subarray(0, 2)), [0xff, 0xd8], "The shown page captures as a JPEG still")
+    assert.equal(await pane.capture(win, "suite", tabID), null, "A hidden page has no still to show")
+    console.log("PASS browser pane still capture")
    const ref = (text: string) => {
      const match = snap.content
        .split("\n")
@@ -209,11 +209,13 @@ export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
  })
  const options = { baseUrl: input.server.endpoint.url, headers: Service.headers(input.server.endpoint) }
  const api = OpenCode.make(options)
-  const location = yield* Effect.tryPromise(() => api.file.list({ location: { directory: process.cwd() } })).pipe(
-    Effect.map((response) => response.location),
-    Effect.catch(() => Effect.tryPromise(() => api.location.get())),
+  const launch = yield* Effect.tryPromise(() => api.file.list({ location: { directory: process.cwd() } })).pipe(
+    Effect.map((response) => ({ location: response.location, fallback: false })),
+    Effect.catch(() =>
+      Effect.tryPromise(() => api.location.get()).pipe(Effect.map((location) => ({ location, fallback: true }))),
+    ),
  )
-  const directory = location.directory
+  const directory = launch.location.directory
  const pluginDirectories = yield* Effect.promise(() => localPluginDirectories(process.cwd(), global.config))
  const handoff = input.terminalHandoff ? yield* Effect.promise(input.terminalHandoff) : undefined
  const managed = input.server.service
@@ -403,7 +405,9 @@ export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
                                                                                packages={input.packages}
                                                                                directories={pluginDirectories}
                                                                              >
-                                                                                <App />
+                                                                                <App
+                                                                                  locationFallback={launch.fallback}
+                                                                                />
                                                                              </PluginProvider>
                                                                            </PanelProvider>
                                                                          </UpdateNotificationProvider>
@@ -456,7 +460,7 @@ export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
  })
 })

-function App() {
+function App(props: { locationFallback: boolean }) {
  const log = useLog({ component: "app" })
  const app = useTuiApp()
  const startup = useTuiStartup()
@@ -473,6 +477,15 @@ function App() {
  const event = useEvent()
  const client = useClient()
  const toast = useToast()
+  onMount(() => {
+    if (!props.locationFallback) return
+    toast.show({
+      variant: "warning",
+      title: "Could not open directory",
+      message: "Using the server default instead. Check the requested directory and its OpenCode config.",
+      duration: 12_000,
+    })
+  })
  const updater = useUpdateNotification()
  const theme = useTheme()
  const { mode, supports, setMode, locked, lock, unlock, afterPaint } = useThemes()
@@ -44,7 +44,7 @@ function segment(value: string) {
  return value
 }

-function createStorage(root: string, channel: string) {
+export function createStorage(root: string, channel: string) {
  const entries = new Map<string, { readonly value: Entry<object>; readonly reload: () => void }>()
  const memories = new Map<string, MemoryEntry<object>>()
  const pending = new Set<Promise<void>>()
@@ -110,18 +110,32 @@ function createStorage(root: string, channel: string) {
    },
  }

-  let reload: ReturnType<typeof setTimeout> | undefined
-  const watcher = watch(directory, () => {
-    clearTimeout(reload)
-    // Atomic writes notify for the temporary file before its final rename, and some
-    // platforms coalesce the rename event. Reload after the event burst has settled.
-    reload = setTimeout(() => entries.forEach((entry) => entry.reload()), 50)
-  })
+  let reloadTimer: ReturnType<typeof setTimeout> | undefined
+  let watcher: ReturnType<typeof watch> | undefined
+  try {
+    watcher = watch(directory, () => {
+      clearTimeout(reloadTimer)
+      // Atomic writes notify for the temporary file before its final rename, and some
+      // platforms coalesce the rename event. Reload after the event burst has settled.
+      reloadTimer = setTimeout(() => entries.forEach((entry) => entry.reload()), 50)
+    })
+    watcher.on("error", (error) => {
+      clearTimeout(reloadTimer)
+      watcher?.close()
+      watcher = undefined
+      console.error("Storage directory watcher failed, live-reload disabled", { directory, error })
+    })
+  } catch (error) {
+    // fs.watch throws synchronously (e.g. ENOSPC when the inotify watch limit is
+    // exhausted). Losing cross-process live-reload is recoverable; crashing the
+    // whole TUI over it is not, so degrade instead of propagating.
+    console.error("Failed to watch storage directory, live-reload disabled", { directory, error })
+  }
  return {
    storage,
    close: () => {
-      clearTimeout(reload)
-      watcher.close()
+      clearTimeout(reloadTimer)
+      watcher?.close()
    },
  }
 }
@@ -924,6 +924,11 @@ test.each([false, true])("uses the resolved launch directory for new prompts (fa

  await setup.ready
  await setup.waitForFrame((frame) => frame.includes("Build · Remote Model Provider"))
+  if (fallback) {
+    await setup.waitForFrame((frame) => frame.includes("Could not open directory"))
+  } else {
+    expect(setup.captureCharFrame()).not.toContain("Could not open directory")
+  }
  setup.mockInput.pressKey("F6")
  await setup.renderOnce()
  await setup.mockInput.typeText("REMOTE_READY")
@@ -951,6 +956,31 @@ test.each([false, true])("uses the resolved launch directory for new prompts (fa
  ).toBe(true)
 })

+test.each([100, 44])("shows a failed launch location in the TUI at width %s", async (width) => {
+  await using state = await tmpdir()
+  const requested = process.cwd()
+  const fallback = { directory, project: { id: "project", directory, canonical: directory } }
+  const requests: URL[] = []
+  await using setup = await createAppFixture({
+    width,
+    state: state.path,
+    fetch: (url) => {
+      requests.push(url)
+      if (url.pathname === "/api/fs/list") return new Response(null, { status: 500 })
+      if (url.pathname === "/api/location") return json(fallback)
+      return undefined
+    },
+  })
+  await setup.ready
+  const frame = await setup.waitForFrame((frame) => frame.includes("Could not open directory"))
+  expect(frame).toContain("OpenCode")
+  expect(frame).toContain("config.")
+  expect(requests[0]?.searchParams.get("location[directory]")).toBe(requested)
+  expect(requests.some((url) => url.pathname === "/api/location" && !url.searchParams.has("location[directory]"))).toBe(
+    true,
+  )
+})
+
 test("error investigations repeatedly seed editable home drafts without creating sessions", async () => {
  const cwd = process.cwd()
  const location = { directory: cwd, project: { id: "project", directory: cwd } }
@@ -0,0 +1,37 @@
+import { afterEach, expect, spyOn, test } from "bun:test"
+import * as fs from "fs"
+import { mkdtempSync, rmSync } from "fs"
+import { tmpdir } from "os"
+import path from "path"
+import { createStorage } from "../../src/context/storage"
+
+afterEach(() => {
+  spyOn(fs, "watch").mockRestore()
+})
+
+test("createStorage degrades gracefully when fs.watch throws (e.g. ENOSPC)", async () => {
+  const dir = mkdtempSync(path.join(tmpdir(), "storage-test-"))
+  // fs.watch throws synchronously when inotify_add_watch fails (e.g. the watch
+  // limit is exhausted). Simulate that scoped to this test only.
+  spyOn(fs, "watch").mockImplementation(() => {
+    throw Object.assign(new Error("ENOSPC: no space left on device, watch '/some/dir'"), { code: "ENOSPC" })
+  })
+
+  try {
+    let result: ReturnType<typeof createStorage> | undefined
+    expect(() => {
+      result = createStorage(dir, "next")
+    }).not.toThrow()
+
+    // storage should still be usable even though the live-reload watcher failed to attach
+    const [store, update] = result!.storage.store("kv", { initial: { count: 0 } })
+    expect(store.count).toBe(0)
+    await update((draft) => {
+      draft.count = 1
+    })
+    expect(store.count).toBe(1)
+    expect(() => result!.close()).not.toThrow()
+  } finally {
+    rmSync(dir, { recursive: true, force: true })
+  }
+})
@@ -155,6 +155,26 @@ export interface MenuSubTriggerProps extends ComponentProps<typeof DropdownMenu.
  badge?: JSX.Element | string
 }

+export interface MenuSubProps extends ComponentProps<typeof DropdownMenu.Sub> {
+  placement?:
+    | "top"
+    | "top-start"
+    | "top-end"
+    | "bottom"
+    | "bottom-start"
+    | "bottom-end"
+    | "left"
+    | "left-start"
+    | "left-end"
+    | "right"
+    | "right-start"
+    | "right-end"
+}
+
+function MenuSub(props: MenuSubProps) {
+  return <DropdownMenu.Sub {...props} />
+}
+
 function MenuSubTrigger(props: ParentProps<MenuSubTriggerProps>) {
  const ctx = useMenuContext()
  const [s, r] = splitProps(props, ["class", "classList", "children", "shortcut", "badge"])
@@ -282,7 +302,7 @@ export const Menu = Object.assign(MenuRoot, {
  Group: DropdownMenu.Group,
  GroupLabel: MenuGroupLabel,
  Separator: MenuSeparator,
-  Sub: DropdownMenu.Sub,
+  Sub: MenuSub,
  SubTrigger: MenuSubTrigger,
  SubContent: MenuSubContent,
  Context: MenuContext,
Author	SHA1	Message	Date
rekram1-node	af8eb4403c	fix(tui): warn when launch directory falls back	2026-09-25 05:27:22 +00:00
Aiden Cline	5335347e80	feat(codemode): add WeakMap and WeakSet (#51257 )	2026-09-25 00:15:19 -05:00
Aiden Cline	16b18dff13	Revert "fix(core): fit model limits and recover compaction overflow" (#51273 )	2026-09-25 00:12:14 -05:00
Aiden Cline	61c2349cef	fix(core): fit model limits and recover compaction overflow (#51238 )	2026-09-25 00:11:40 -05:00
opencode-agent[bot]andBrendonovich	684721efb8	feat(app): add provider account switching (#51266 ) Co-authored-by: Brendonovich <Brendonovich@users.noreply.github.com>	2026-09-25 05:03:33 +00:00
Aiden Cline	962c14a49c	fix(codemode): honor thisArg, program toString in computed keys, and ToPrimitive in String and Number arguments (#51264 )	2026-09-24 23:46:15 -05:00
opencode-agent[bot]andrekram1-node	85b98e7da4	fix(tui): handle storage watcher errors after startup (#51243 ) Co-authored-by: rekram1-node <rekram1-node@users.noreply.github.com>	2026-09-24 20:25:06 -05:00
Aiden Cline	8061220b08	test(codemode): vendor every eligible test262 directory and bound unsupported globals (#51242 )	2026-09-24 20:19:24 -05:00
Luke Parker	b02cc35f13	fix(desktop): keep browser page visible under floating content (#51240 )	2026-09-25 10:35:17 +10:00
Aiden Cline	e23d89c9a9	fix(codemode): destructure object patterns from primitives and convert Date components through ToPrimitive (#51239 )	2026-09-24 19:32:19 -05:00
ARH Alireza Haghdoost Claude Sonnet 5	e8b3e19e85	fix(tui): don't crash when fs.watch throws (e.g. ENOSPC) (#51210 ) Co-authored-by: Alireza Haghdoost <haghdoost@uber.com> Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>	2026-09-24 19:16:43 -05:00
Aiden Cline	5256f30957	feat(codemode): honor program valueOf and toString in operators and conversions (#50837 )	2026-09-24 18:45:48 -05:00