diff --git a/packages/codemode/src/codemode.ts b/packages/codemode/src/codemode.ts
index 35a96c4a7e..1f99c01e74 100644
--- a/packages/codemode/src/codemode.ts
+++ b/packages/codemode/src/codemode.ts
@@ -120,13 +120,6 @@ export type Runtime<R = never> = {
   readonly execute: (code: string) => Effect.Effect<Result, never, R>
 }
 
-export const description = [
-  "Run JavaScript in a confined Code Mode runtime through { code }.",
-  "Call Code Mode tools through `tools` using the exact paths and signatures from the instructions.",
-  "Use `search({ query })` to discover exact signatures when needed.",
-  "Await important calls and use `Promise.all` for independent calls.",
-].join("\n")
-
 const validateLimit = (name: keyof ExecutionLimits, value: number | undefined, minimum: number): number | undefined => {
   if (value !== undefined && (!Number.isSafeInteger(value) || value < minimum)) {
     throw new RangeError(`${name} must be a safe integer greater than or equal to ${minimum}.`)
diff --git a/packages/codemode/test/codemode.test.ts b/packages/codemode/test/codemode.test.ts
index f884875915..e2c91e7f4e 100644
--- a/packages/codemode/test/codemode.test.ts
+++ b/packages/codemode/test/codemode.test.ts
@@ -550,23 +550,6 @@ describe("CodeMode schema flexibility", () => {
 })
 
 describe("CodeMode public contract", () => {
-  test("keeps the tool description independent from the catalog", () => {
-    const runtime = CodeMode.make({
-      tools: {
-        lookup: Tool.make({
-          description: "Look up a record",
-          input: Schema.Struct({}),
-          output: Schema.String,
-          run: () => Effect.succeed("found"),
-        }),
-      },
-    })
-
-    expect(CodeMode.description).toContain("confined Code Mode runtime")
-    expect(CodeMode.description).not.toContain("lookup")
-    expect(runtime.instructions()).toContain("tools.lookup(input:")
-  })
-
   const lookup = Tool.make({
     description: "Look up an order by ID",
     input: Schema.Struct({ id: Schema.String }),
diff --git a/packages/core/src/tool/execute.ts b/packages/core/src/tool/execute.ts
index de062dd372..b9ffa751e3 100644
--- a/packages/core/src/tool/execute.ts
+++ b/packages/core/src/tool/execute.ts
@@ -42,9 +42,17 @@ export interface Registration {
   readonly namespace?: string
 }
 
+// Invariant model-facing guidance; the changing tool catalog is delivered through Instructions.
+const description = [
+  "Run JavaScript in a confined Code Mode runtime through { code }.",
+  "Call Code Mode tools through `tools` using the exact paths and signatures from the instructions.",
+  "Use `search({ query })` to discover exact signatures when needed.",
+  "Await important calls and use `Promise.all` for independent calls.",
+].join("\n")
+
 export const create = (registrations: ReadonlyMap<string, Registration>) => {
   return make({
-    description: CodeMode.description,
+    description,
     input: CodeMode.Input,
     output: ExecuteOutput,
     structured: ExecuteMetadata,