diff --git a/packages/codemode/README.md b/packages/codemode/README.md
index e8447e09b2..22af0b701b 100644
--- a/packages/codemode/README.md
+++ b/packages/codemode/README.md
@@ -15,7 +15,7 @@ runs, no sandbox required.
 The deliberate differences:
 
 - **No ambient authority.** No `fetch`, `process`, filesystem, timers, or host globals - only the allowlisted standard
-  library and the `tools` tree.
+  library and supplied `tools`.
 - **No dynamic code.** No `eval`, `Function`, or module loading.
 - **Plain-data boundaries.** Tool arguments and program results are JSON-like data. Dates become ISO strings, RegExp,
   Map, and Set serialize as `{}`, and promises, functions, and runtime references cannot cross the boundary.
@@ -33,8 +33,8 @@ generators, and full sparse-array parity) are tracked as unchecked items in the
 ## Quick Start
 
 The package is workspace-private (`"@opencode-ai/codemode": "workspace:*"`). Hosts interact with it through `effect`
-and should depend on `effect` themselves. Define tools with Effect Schema, then place them in the object tree exposed
-to programs as `tools`:
+and should depend on `effect` themselves. Define tools with Effect Schema, then expose them to programs through
+`tools`:
 
 ```ts
 import { CodeMode, Tool } from "@opencode-ai/codemode"
@@ -94,8 +94,8 @@ Effect-returning and must not fail.
 
 ### OpenAPI tools
 
-`OpenAPI.fromSpec` turns an OpenAPI 3.x document into a tool subtree - one tool per operation, namespaced by dotted
-`operationId`:
+`OpenAPI.fromSpec` turns an OpenAPI 3.x document into namespaced tools - one tool per operation, using dotted
+`operationId` segments as namespaces:
 
 ```ts
 const api = OpenAPI.fromSpec({ spec, auth: { resolve } })
diff --git a/packages/codemode/src/codemode.ts b/packages/codemode/src/codemode.ts
index c53c7b40ab..1f99c01e74 100644
--- a/packages/codemode/src/codemode.ts
+++ b/packages/codemode/src/codemode.ts
@@ -1,7 +1,7 @@
 import { Effect, Schema } from "effect"
 import { executeWithLimits } from "./interpreter/execute.js"
-import { type HostTools, type Services, type ToolDescription, ToolRuntime } from "./tool-runtime.js"
-import type { Definition } from "./tool.js"
+import { type Services, type ToolDescription, ToolRuntime } from "./tool-runtime.js"
+import type { Tools } from "./tools.js"
 
 /** A tool call admitted during an execution. */
 export type { ToolCall, ToolCallEnded, ToolCallHooks, ToolCallStarted, ToolDescription } from "./tool-runtime.js"
@@ -28,10 +28,6 @@ export type DiscoveryOptions = {
   readonly catalogBudget?: number
 }
 
-type ToolTree<R = never> = {
-  readonly [name: string]: Definition<R> | ToolTree<R>
-}
-
 export type ResolvedExecutionLimits = {
   readonly timeoutMs: number | undefined
   readonly maxToolCalls: number | undefined
@@ -39,24 +35,24 @@ export type ResolvedExecutionLimits = {
 }
 
 /** Options for one CodeMode execution. */
-export type ExecuteOptions<Tools extends Record<string, unknown> = {}> = {
+export type ExecuteOptions<Provided extends Record<string, unknown> = {}> = {
   /** Source for one program in the supported JavaScript subset. */
   code: string
-  /** Explicit tool tree exposed to the program as `tools`. */
-  tools?: Tools & ToolTree<Services<Tools>>
+  /** Explicit tools exposed to the program as `tools`. */
+  tools?: Provided & Tools<Services<Provided>>
   /** Per-execution overrides for the default resource limits. */
   limits?: ExecutionLimits
   /** Observes decoded tool input immediately before tool execution. */
-  onToolCallStart?: (call: ToolRuntime.ToolCallStarted) => Effect.Effect<void, never, Services<Tools>>
+  onToolCallStart?: (call: ToolRuntime.ToolCallStarted) => Effect.Effect<void, never, Services<Provided>>
   /** Observes each admitted tool call as it settles, with outcome and duration. */
-  onToolCallEnd?: (call: ToolRuntime.ToolCallEnded) => Effect.Effect<void, never, Services<Tools>>
+  onToolCallEnd?: (call: ToolRuntime.ToolCallEnded) => Effect.Effect<void, never, Services<Provided>>
 }
 
 /** A JSON value that can cross the confined interpreter boundary. */
 export type DataValue = Schema.Json
 
 /** Configuration shared by `CodeMode.make` and `CodeMode.execute`. */
-export type Options<Tools extends Record<string, unknown> = {}> = Omit<ExecuteOptions<Tools>, "code"> & {
+export type Options<Provided extends Record<string, unknown> = {}> = Omit<ExecuteOptions<Provided>, "code"> & {
   /** Progressive-disclosure configuration for the agent-facing tool catalog. */
   readonly discovery?: DiscoveryOptions
 }
@@ -117,7 +113,7 @@ export const Result = Schema.Union([Success, Failure])
 /** Result of executing a CodeMode program. Program failures are data, not Effect failures. */
 export type Result = typeof Result.Type
 
-/** Reusable confined runtime over one explicit tool tree. */
+/** Reusable confined runtime over explicit tools. */
 export type Runtime<R = never> = {
   readonly catalog: () => ReadonlyArray<ToolDescription>
   readonly instructions: () => string
@@ -138,24 +134,24 @@ const resolveExecutionLimits = (limits?: ExecutionLimits): ResolvedExecutionLimi
 })
 
 /** Executes one Effect-native CodeMode program without constructing a reusable runtime. */
-export const execute = <const Tools extends Record<string, unknown>>(
-  options: ExecuteOptions<Tools>,
-): Effect.Effect<Result, never, Services<Tools>> => {
-  const tools = (options.tools ?? {}) as HostTools<Services<Tools>>
+export const execute = <const Provided extends Record<string, unknown>>(
+  options: ExecuteOptions<Provided>,
+): Effect.Effect<Result, never, Services<Provided>> => {
+  const tools = (options.tools ?? {}) as Tools<Services<Provided>>
   return executeWithLimits(options, resolveExecutionLimits(options.limits), ToolRuntime.searchIndex(tools))
 }
 
 /** Creates an Effect-native runtime over explicit, schema-described tools. */
-export const make = <const Tools extends Record<string, unknown> = {}>(
-  options: Options<Tools> = {} as Options<Tools>,
-): Runtime<Services<Tools>> => {
-  const tools = (options.tools ?? {}) as HostTools<Services<Tools>>
+export const make = <const Provided extends Record<string, unknown> = {}>(
+  options: Options<Provided> = {} as Options<Provided>,
+): Runtime<Services<Provided>> => {
+  const tools = (options.tools ?? {}) as Tools<Services<Provided>>
   const limits = resolveExecutionLimits(options.limits)
   const prepared = ToolRuntime.prepare(tools, options.discovery?.catalogBudget)
 
   return {
     catalog: () => prepared.catalog,
     instructions: () => prepared.instructions,
-    execute: (code) => executeWithLimits<Tools>({ ...options, code }, limits, prepared.searchIndex),
+    execute: (code) => executeWithLimits<Provided>({ ...options, code }, limits, prepared.searchIndex),
   }
 }
diff --git a/packages/codemode/src/interpreter/execute.ts b/packages/codemode/src/interpreter/execute.ts
index 1e81a0bfca..5fcd708752 100644
--- a/packages/codemode/src/interpreter/execute.ts
+++ b/packages/codemode/src/interpreter/execute.ts
@@ -2,17 +2,18 @@ import { parse } from "acorn"
 import { Cause, Effect, Scope } from "effect"
 import { DiagnosticCategory, ModuleKind, ScriptTarget, flattenDiagnosticMessageText, transpileModule } from "typescript"
 import type { DataValue, Diagnostic, ExecuteOptions, ResolvedExecutionLimits, Result } from "../codemode.js"
-import { copyIn, copyOut, ToolRuntime, type HostTools, type Services } from "../tool-runtime.js"
+import { copyIn, copyOut, ToolRuntime, type Services } from "../tool-runtime.js"
+import type { Tools } from "../tools.js"
 import { normalizeError } from "./errors.js"
 import { InterpreterRuntimeError, isRecord, type ProgramNode } from "./model.js"
 import { PromiseRuntime } from "./promises.js"
 import { Interpreter } from "./runtime.js"
 
-export const executeWithLimits = <const Tools extends Record<string, unknown>>(
-  options: ExecuteOptions<Tools>,
+export const executeWithLimits = <const Provided extends Record<string, unknown>>(
+  options: ExecuteOptions<Provided>,
   limits: ResolvedExecutionLimits,
   searchIndex: ToolRuntime.DiscoveryPlan["searchIndex"],
-): Effect.Effect<Result, never, Services<Tools>> => {
+): Effect.Effect<Result, never, Services<Provided>> => {
   if (options.code.trim().length === 0) {
     return Effect.succeed({
       ok: false,
@@ -24,7 +25,7 @@ export const executeWithLimits = <const Tools extends Record<string, unknown>>(
   // Allocate execution state inside suspension so reused Effects never share it.
   return Effect.suspend(() => {
     const tools = ToolRuntime.make(
-      (options.tools ?? {}) as HostTools<Services<Tools>>,
+      (options.tools ?? {}) as Tools<Services<Provided>>,
       limits.maxToolCalls,
       searchIndex,
       {
@@ -35,15 +36,21 @@ export const executeWithLimits = <const Tools extends Record<string, unknown>>(
     const logs: Array<string> = []
     const logged = () => (logs.length > 0 ? { logs: [...logs] } : {})
     // Set only after copy-out so timeouts cannot report invalid values as completed.
-    let returned: { value: DataValue; promises: PromiseRuntime<Services<Tools>> } | undefined
+    let returned: { value: DataValue; promises: PromiseRuntime<Services<Provided>> } | undefined
 
     const base = Effect.acquireUseRelease(
       Scope.make("parallel"),
       (scope) =>
         Effect.gen(function* () {
           const program = parseProgram(options.code)
-          const promises = new PromiseRuntime<Services<Tools>>(scope)
-          const interpreter = new Interpreter<Services<Tools>>(tools.invoke, tools.search, tools.keys, promises, logs)
+          const promises = new PromiseRuntime<Services<Provided>>(scope)
+          const interpreter = new Interpreter<Services<Provided>>(
+            tools.invoke,
+            tools.search,
+            tools.keys,
+            promises,
+            logs,
+          )
           const value = yield* interpreter.run(program)
           const result = copyOut(copyIn(value, "Execution result"), true) as DataValue
           returned = { value: result, promises }
diff --git a/packages/codemode/src/openapi/types.ts b/packages/codemode/src/openapi/types.ts
index 6f3eb86283..252f49d86c 100644
--- a/packages/codemode/src/openapi/types.ts
+++ b/packages/codemode/src/openapi/types.ts
@@ -61,7 +61,7 @@ export type Skipped = {
 export type Tools = { [name: string]: Definition<HttpClient.HttpClient> | Tools }
 
 export type Result = {
-  /** Tool subtree; the host places it under a key in its `tools` tree. */
+  /** Namespaced tools; the host places them under a key in its `tools` object. */
   readonly tools: Tools
   readonly skipped: ReadonlyArray<Skipped>
 }
diff --git a/packages/codemode/src/tool-runtime.ts b/packages/codemode/src/tool-runtime.ts
index 09cea8b53d..d4ed4ea221 100644
--- a/packages/codemode/src/tool-runtime.ts
+++ b/packages/codemode/src/tool-runtime.ts
@@ -9,6 +9,7 @@ import {
   outputTypeScript,
 } from "./tool-schema.js"
 import { isDefinition as isToolDefinition, type Definition } from "./tool.js"
+import type { Tools } from "./tools.js"
 import {
   CodeModeDate,
   CodeModeMap,
@@ -21,28 +22,20 @@ import {
 
 const estimateTokens = (input: string) => Math.max(0, Math.round(input.length / 4))
 
-export type HostTool<R = never> = (...args: Array<unknown>) => Effect.Effect<unknown, unknown, R>
+export type Services<T> = ServicesOf<T, []>
 
-export type HostTools<R = never> = {
-  [name: string]: HostTool<R> | Definition<R> | HostTools<R>
-}
-
-export type Services<Tools> = ServicesOf<Tools, []>
-
-type ServicesOf<Tools, Depth extends ReadonlyArray<unknown>> = Depth["length"] extends 8
+type ServicesOf<T, Depth extends ReadonlyArray<unknown>> = Depth["length"] extends 8
   ? never
-  : Tools extends (...args: Array<unknown>) => Effect.Effect<unknown, unknown, infer R>
+  : T extends {
+        readonly _tag: "CodeModeTool"
+        readonly run: (input: unknown) => Effect.Effect<unknown, unknown, infer R>
+      }
     ? R
-    : Tools extends {
-          readonly _tag: "CodeModeTool"
-          readonly run: (input: unknown) => Effect.Effect<unknown, unknown, infer R>
-        }
-      ? R
-      : Tools extends object
-        ? string extends keyof Tools
-          ? ServicesOf<Tools[string], [...Depth, unknown]>
-          : ServicesOf<Tools[keyof Tools], [...Depth, unknown]>
-        : never
+    : T extends object
+      ? string extends keyof T
+        ? ServicesOf<T[string], [...Depth, unknown]>
+        : ServicesOf<T[keyof T], [...Depth, unknown]>
+      : never
 
 export type ToolCall = {
   readonly name: string
@@ -125,7 +118,7 @@ export class ToolRuntimeError extends Error {
   }
 }
 
-const isDefinition = <R>(value: HostTool<R> | Definition<R> | HostTools<R>): value is Definition<R> =>
+const isDefinition = <R>(value: Definition<R> | Tools<R>): value is Definition<R> =>
   isToolDefinition<R>(value)
 
 const runHost = <A, E, R>(effect: Effect.Effect<A, E, R>): Effect.Effect<A, ToolError, R> =>
@@ -282,13 +275,13 @@ export const copyOut = (value: unknown, undefinedAsNull = false): unknown => {
 }
 
 const definitions = <R>(
-  tools: HostTools<R>,
+  tools: Tools<R>,
   path: ReadonlyArray<string> = [],
 ): Array<{ path: string; definition: Definition<R> }> =>
   Object.entries(tools).flatMap(([name, value]) => {
     const next = [...path, name]
     if (isDefinition(value)) return [{ path: next.join("."), definition: value }]
-    return typeof value === "function" ? [] : definitions(value, next)
+    return definitions(value, next)
   })
 
 const describeDefinition = <R>(path: string, definition: Definition<R>): ToolDescription => ({
@@ -297,7 +290,7 @@ const describeDefinition = <R>(path: string, definition: Definition<R>): ToolDes
   signature: `${toolExpression(path)}(input: ${inputTypeScript(definition, true)}): Promise<${outputTypeScript(definition, true)}>`,
 })
 
-const visibleDefinitions = <R>(tools: HostTools<R>) =>
+const visibleDefinitions = <R>(tools: Tools<R>) =>
   definitions(tools).map(({ path, definition }) => ({
     path,
     definition,
@@ -415,11 +408,11 @@ const toSearchEntry = <R>(path: string, definition: Definition<R>, description:
     .toLowerCase(),
 })
 
-export const searchIndex = <R>(tools: HostTools<R>): ReadonlyArray<SearchEntry> =>
+export const searchIndex = <R>(tools: Tools<R>): ReadonlyArray<SearchEntry> =>
   visibleDefinitions(tools).map(({ path, definition, description }) => toSearchEntry(path, definition, description))
 
 // Budget signatures round-robin so every namespace remains visible.
-export const prepare = <R>(tools: HostTools<R>, catalogBudget = defaultCatalogBudget): DiscoveryPlan => {
+export const prepare = <R>(tools: Tools<R>, catalogBudget = defaultCatalogBudget): DiscoveryPlan => {
   if (!Number.isSafeInteger(catalogBudget) || catalogBudget < 0) {
     throw new RangeError("discovery.catalogBudget must be a non-negative safe integer")
   }
@@ -562,43 +555,33 @@ export const prepare = <R>(tools: HostTools<R>, catalogBudget = defaultCatalogBu
   }
 }
 
-const namespaceKeys = <R>(tools: HostTools<R>, path: ReadonlyArray<string>): ReadonlyArray<string> => {
-  let value: HostTool<R> | Definition<R> | HostTools<R> = tools
+const namespaceKeys = <R>(tools: Tools<R>, path: ReadonlyArray<string>): ReadonlyArray<string> => {
+  let value: Definition<R> | Tools<R> = tools
   for (const segment of path) {
-    if (
-      isBlockedMember(segment) ||
-      typeof value === "function" ||
-      isDefinition(value) ||
-      !Object.hasOwn(value, segment)
-    ) {
+    if (isBlockedMember(segment) || isDefinition(value) || !Object.hasOwn(value, segment)) {
       throw new ToolRuntimeError("UnknownTool", `Unknown tool namespace '${path.join(".")}'.`, [
         "Object.keys(tools) lists the available namespaces; search({ query }) finds described tools.",
       ])
     }
-    value = value[segment] as HostTool<R> | Definition<R> | HostTools<R>
+    value = value[segment] as Definition<R> | Tools<R>
   }
-  if (typeof value === "function" || isDefinition(value)) return []
+  if (isDefinition(value)) return []
   return Object.keys(value)
 }
 
-const resolve = <R>(tools: HostTools<R>, path: ReadonlyArray<string>): HostTool<R> | Definition<R> => {
-  let value: HostTool<R> | Definition<R> | HostTools<R> = tools
+const resolve = <R>(tools: Tools<R>, path: ReadonlyArray<string>): Definition<R> => {
+  let value: Definition<R> | Tools<R> = tools
 
   for (const segment of path) {
-    if (
-      isBlockedMember(segment) ||
-      typeof value === "function" ||
-      isDefinition(value) ||
-      !Object.hasOwn(value, segment)
-    ) {
+    if (isBlockedMember(segment) || isDefinition(value) || !Object.hasOwn(value, segment)) {
       throw new ToolRuntimeError("UnknownTool", `Unknown tool '${path.join(".")}'.`, [
         "Use search({ query }) to find available described tools.",
       ])
     }
-    value = value[segment] as HostTool<R> | Definition<R> | HostTools<R>
+    value = value[segment] as Definition<R> | Tools<R>
   }
 
-  if (typeof value !== "function" && !isDefinition(value)) {
+  if (!isDefinition(value)) {
     throw new ToolRuntimeError("UnknownTool", `Tool '${path.join(".")}' is not callable.`)
   }
 
@@ -614,7 +597,7 @@ export type ToolRuntime<R = never> = {
 }
 
 export const make = <R>(
-  tools: HostTools<R>,
+  tools: Tools<R>,
   maxToolCalls: number | undefined,
   searchIndex: ReadonlyArray<SearchEntry>,
   hooks?: ToolCallHooks<R>,
@@ -701,14 +684,7 @@ export const make = <R>(
         const name = path.join(".")
         const externalArgs = args.map((arg) => copyOut(copyIn(arg, `Arguments for tool '${name}'`)))
         const tool = resolve(tools, path)
-        if (isDefinition(tool)) return yield* invokeDefinition(name, tool, externalArgs)
-        const index = yield* recordAndObserve(name, externalArgs)
-        return yield* observeEnd(
-          Effect.gen(function* () {
-            return yield* decodeOutput(yield* runHost(Effect.suspend(() => tool(...externalArgs))), name)
-          }),
-          { index, name, input: externalArgs },
-        )
+        return yield* invokeDefinition(name, tool, externalArgs)
       }),
   }
 }
diff --git a/packages/codemode/src/tool.ts b/packages/codemode/src/tool.ts
index 0535cc9caa..4d07a6398c 100644
--- a/packages/codemode/src/tool.ts
+++ b/packages/codemode/src/tool.ts
@@ -29,7 +29,7 @@ export type JsonSchema = {
 /** Either a validating Effect Schema or a render-only JSON Schema document. */
 export type SchemaType = Schema.Decoder<unknown> | JsonSchema
 
-/** Schema-backed tool definition consumed by a CodeMode tool tree. */
+/** Schema-backed tool definition exposed through CodeMode's `tools` object. */
 export type Definition<R = never> = {
   readonly _tag: "CodeModeTool"
   readonly description: string
diff --git a/packages/codemode/src/tools.ts b/packages/codemode/src/tools.ts
new file mode 100644
index 0000000000..04e36dcef2
--- /dev/null
+++ b/packages/codemode/src/tools.ts
@@ -0,0 +1,5 @@
+import type { Definition } from "./tool.js"
+
+export type Tools<R = never> = {
+  readonly [name: string]: Definition<R> | Tools<R>
+}
diff --git a/packages/codemode/test/enumeration.test.ts b/packages/codemode/test/enumeration.test.ts
index ca71226a57..0cd81e9c7e 100644
--- a/packages/codemode/test/enumeration.test.ts
+++ b/packages/codemode/test/enumeration.test.ts
@@ -3,7 +3,7 @@ import { Effect, Schema } from "effect"
 import { CodeMode, Tool } from "../src/index.js"
 
 // Key enumeration: Object.keys and for...in share one surface over plain objects, arrays
-// (index strings), and tool references (namespace/tool names from the host tool tree), so a
+// (index strings), and tool references (namespace/tool names from the supplied tools), so a
 // model can discover what it may call instead of guessing names from the instructions. The
 // motivating transcript: `Object.keys(tools)` failed with the generic plain-objects-only
 // message and `for (const key in tools)` was unsupported syntax, forcing blind guesses.
@@ -137,7 +137,7 @@ describe("for...in", () => {
     ).toBe("only")
   })
 
-  test("enumerates namespaces and tools from the callable tool tree", async () => {
+  test("enumerates namespaces and tools from the supplied tools", async () => {
     expect(
       await value(`
       const names = []