fix: separate instructions from API declaration to prevent API error

packages/core/src/tools/definitions/resolver.ts

@@ -12,23 +12,38 @@ import type { ToolDefinition } from './types.js';
  *
  * @param definition The tool definition containing the base declaration and optional overrides.
  * @param modelId Optional model identifier to apply specific overrides.
- * @returns The FunctionDeclaration to be sent to the API.
+ * @returns An object containing the FunctionDeclaration for the API and optional instructions for the system prompt.
  */
 export function resolveToolDeclaration(
   definition: ToolDefinition,
   modelId?: string,
-): FunctionDeclaration & { instructions?: string } {
+): { declaration: FunctionDeclaration; instructions?: string } {
+  const { instructions: baseInstructions, ...baseDeclaration } =
+    definition.base;
+
   if (!modelId || !definition.overrides) {
-    return definition.base;
+    return {
+      declaration: baseDeclaration,
+      instructions: baseInstructions,
+    };
   }
 
   const override = definition.overrides(modelId);
   if (!override) {
-    return definition.base;
+    return {
+      declaration: baseDeclaration,
+      instructions: baseInstructions,
+    };
   }
 
+  const { instructions: overrideInstructions, ...overrideDeclaration } =
+    override;
+
   return {
-    ...definition.base,
-    ...override,
+    declaration: {
+      ...baseDeclaration,
+      ...overrideDeclaration,
+    },
+    instructions: overrideInstructions ?? baseInstructions,
   };
 }

packages/core/src/tools/edit.ts

@@ -914,19 +914,22 @@ export class EditTool
       typeof config.getActiveModel === 'function'
         ? config.getActiveModel()
         : undefined;
-    const resolved = resolveToolDeclaration(EDIT_DEFINITION, modelId);
+    const { declaration, instructions } = resolveToolDeclaration(
+      EDIT_DEFINITION,
+      modelId,
+    );
     super(
       EditTool.Name,
       EDIT_DISPLAY_NAME,
-      resolved.description!,
+      declaration.description!,
       Kind.Edit,
-      resolved.parametersJsonSchema,
+      declaration.parametersJsonSchema,
       messageBus,
       true, // isOutputMarkdown
       false, // canUpdateOutput
       undefined, // extensionName
       undefined, // extensionId
-      resolved.instructions,
+      instructions,
     );
   }
 
@@ -970,7 +973,7 @@ export class EditTool
   }
 
   override getSchema(modelId?: string) {
-    return resolveToolDeclaration(EDIT_DEFINITION, modelId);
+    return resolveToolDeclaration(EDIT_DEFINITION, modelId).declaration;
   }
 
   getModifyContext(_: AbortSignal): ModifyContext<EditToolParams> {

packages/core/src/tools/read-file.ts

@@ -243,6 +243,6 @@ export class ReadFileTool extends BaseDeclarativeTool<
   }
 
   override getSchema(modelId?: string) {
-    return resolveToolDeclaration(READ_FILE_DEFINITION, modelId);
+    return resolveToolDeclaration(READ_FILE_DEFINITION, modelId).declaration;
   }
 }

packages/core/src/tools/read-many-files.ts

@@ -493,6 +493,7 @@ export class ReadManyFilesTool extends BaseDeclarativeTool<
   }
 
   override getSchema(modelId?: string) {
-    return resolveToolDeclaration(READ_MANY_FILES_DEFINITION, modelId);
+    return resolveToolDeclaration(READ_MANY_FILES_DEFINITION, modelId)
+      .declaration;
   }
 }

packages/core/src/tools/shell.ts

@@ -474,19 +474,22 @@ export class ShellTool extends BaseDeclarativeTool<
       config.getEnableInteractiveShell(),
       config.getEnableShellOutputEfficiency(),
     );
-    const resolved = resolveToolDeclaration(definition, modelId);
+    const { declaration, instructions } = resolveToolDeclaration(
+      definition,
+      modelId,
+    );
     super(
       ShellTool.Name,
       'Shell',
-      resolved.description!,
+      declaration.description!,
       Kind.Execute,
-      resolved.parametersJsonSchema,
+      declaration.parametersJsonSchema,
       messageBus,
       false, // output is not markdown
       true, // output can be updated
       undefined, // extensionName
       undefined, // extensionId
-      resolved.instructions,
+      instructions,
     );
   }
 
@@ -527,6 +530,6 @@ export class ShellTool extends BaseDeclarativeTool<
       this.config.getEnableInteractiveShell(),
       this.config.getEnableShellOutputEfficiency(),
     );
-    return resolveToolDeclaration(definition, modelId);
+    return resolveToolDeclaration(definition, modelId).declaration;
   }
 }

packages/core/src/tools/write-todos.test.ts

@@ -7,9 +7,10 @@
 import { describe, expect, it } from 'vitest';
 import { WriteTodosTool, type WriteTodosToolParams } from './write-todos.js';
 import { createMockMessageBus } from '../test-utils/mock-message-bus.js';
+import { makeFakeConfig } from '../test-utils/config.js';
 
 describe('WriteTodosTool', () => {
-  const tool = new WriteTodosTool(createMockMessageBus());
+  const tool = new WriteTodosTool(makeFakeConfig(), createMockMessageBus());
   const signal = new AbortController().signal;
 
   describe('validation', () => {

packages/core/src/tools/write-todos.ts

@@ -90,24 +90,33 @@ export class WriteTodosTool extends BaseDeclarativeTool<
       typeof config.getActiveModel === 'function'
         ? config.getActiveModel()
         : undefined;
-    const resolved = resolveToolDeclaration(WRITE_TODOS_DEFINITION, modelId);
+    const { declaration, instructions } = resolveToolDeclaration(
+      WRITE_TODOS_DEFINITION,
+      modelId,
+    );
     super(
       WriteTodosTool.Name,
       'WriteTodos',
-      resolved.description!,
+      declaration.description!,
       Kind.Other,
-      resolved.parametersJsonSchema,
+      declaration.parametersJsonSchema,
       messageBus,
       true, // isOutputMarkdown
       false, // canUpdateOutput
       undefined, // extensionName
       undefined, // extensionId
-      resolved.instructions,
+      instructions,
     );
   }
 
   override getSchema(modelId?: string) {
-    return resolveToolDeclaration(WRITE_TODOS_DEFINITION, modelId);
+    const activeModel =
+      modelId ??
+      (typeof this.config.getActiveModel === 'function'
+        ? this.config.getActiveModel()
+        : undefined);
+    return resolveToolDeclaration(WRITE_TODOS_DEFINITION, activeModel)
+      .declaration;
   }
 
   protected override validateToolParamValues(