fix: name run_code's required description argument in its model-facing prose

The transport schema requires both `code` and `description`, but the tool
description and both SDK instruction flavors described the call as passing a
program. `description` was reachable only through the parameter schema, so a
model following the prose emitted `{code}` alone and lost the whole written
program to an INVALID_ARGS rejection.

The length and format guidance stays in RUN_CODE_DESCRIPTION_PARAM_DESCRIPTION
alone, so the schema and the prompt cannot drift.

Fixes #2426

packages/core/tools/tests/code-mode.spec.ts

@@ -399,6 +399,10 @@ describe('mode-aware wire contribution', () => {
     const runCodeSchema = assembly.tools.find(tool => tool.name === RUN_CODE_NAME)
     expect(runCodeSchema?.description).toContain('Execute a TypeScript program')
     expect(runCodeSchema?.description).toContain('BODY of an')
+    // Both required arguments are named here, not only in the parameter
+    // schema: prose that describes the call as "pass the program" is what
+    // leads a model to emit `{code}` alone and fail INVALID_ARGS.
+    expect(runCodeSchema?.description).toContain('`description`')
     const codeParam = (runCodeSchema?.parameters as { properties: { code: { description: string } } }).properties.code
     expect(codeParam.description).toBe('The program: the body of an async TypeScript function.')
   })
@@ -410,6 +414,7 @@ describe('mode-aware wire contribution', () => {
     const runCodeSchema = assembly.tools.find(tool => tool.name === RUN_CODE_NAME)
     expect(runCodeSchema?.description).toContain('Execute a Python program')
     expect(runCodeSchema?.description).toContain('`return <value>`')
+    expect(runCodeSchema?.description).toContain('`description`')
     expect(runCodeSchema?.description).not.toContain('TypeScript')
     const codeParam = (runCodeSchema?.parameters as { properties: { code: { description: string } } }).properties.code
     expect(codeParam.description).toBe('The program: the body of an async Python function.')

packages/core/tools/tests/py-types.spec.ts

@@ -166,6 +166,15 @@ describe('renderToolsSdkPy', () => {
     expect(text).toContain('tools: Tools')
   })
 
+  it('names both required call arguments, not just the program', () => {
+    // The schema requires `code` AND `description`; instructions that mention
+    // only the program let a model emit `{code}` alone and fail INVALID_ARGS.
+    const text = renderToolsSdkPy([bash])
+    expect(text).toContain('`code`')
+    expect(text).toContain('`description`')
+    expect(text).toContain('two required arguments')
+  })
+
   it('renders required as plain fields and optional as NotRequired, with per-field description comments', () => {
     const tool: ToolSdkSchema = {
       name: 'search',

packages/core/tools/tests/ts-types.spec.ts

@@ -148,6 +148,15 @@ describe('renderToolsSdk', () => {
     expect(text).toContain('lossless JSON')
   })
 
+  it('names both required call arguments, not just the program', () => {
+    // The schema requires `code` AND `description`; instructions that mention
+    // only the program let a model emit `{code}` alone and fail INVALID_ARGS.
+    const text = renderToolsSdk([bash])
+    expect(text).toContain('`code`')
+    expect(text).toContain('`description`')
+    expect(text).toContain('two required arguments')
+  })
+
   it('is deterministic: same tool set, byte-identical text regardless of input order', () => {
     expect(renderToolsSdk([bash, exotic])).toBe(renderToolsSdk([exotic, bash]))
     // Equal names sort stably (the comparator's equal arm).