fix(agent-core): gate background questions on task controls

.changeset/guard-background-questions.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Prevent AskUserQuestion from starting background tasks when task controls are unavailable.

packages/agent-core-v2/src/agent/tools/ask-user-question/askUserQuestionTool.ts

@@ -1,11 +1,10 @@
-import { z } from 'zod';
-
 import { CoreErrors } from '#/_base/errors/codes';
 import { Error2 } from '#/_base/errors/errors';
 import { toInputJsonSchema } from '#/tool/input-schema';
 import { isAbortError } from '#/_base/utils/abort';
 import { IAgentTaskService } from '#/agent/task/task';
 import { IAgentScopeContext } from '#/agent/scopeContext/scopeContext';
+import { IAgentToolPolicyService } from '#/agent/toolPolicy/toolPolicy';
 import { ITelemetryService } from '#/app/telemetry/telemetry';
 import type { QuestionAnsweredEvent, QuestionDismissedEvent } from '#/app/telemetry/events';
 import type {
@@ -23,6 +22,7 @@ import type {
   QuestionResult,
 } from '#/session/question/question';
 import {
+  AskUserQuestionInputSchema,
   AskUserQuestionInputSchemaWithBackground,
   IAskUserQuestionTool,
   questionUniquenessError,
@@ -36,20 +36,33 @@ const QUESTION_DISMISSED_MESSAGE = 'User dismissed the question without answerin
 const QUESTION_UNSUPPORTED_FAILURE_MESSAGE =
   'The connected client does not support interactive questions. Do NOT call this tool again. Ask the user directly in your text response instead.';
 
+const BACKGROUND_DESCRIPTION =
+  '- Set background=true when you can keep working without the answer. This starts a background question task and returns a task_id immediately. The answer arrives automatically in a later turn — you do not need to poll, sleep, or check on it. Continue with other work; never fabricate or predict the answer.';
+
+const BACKGROUND_UNAVAILABLE_MESSAGE =
+  'Background questions are not available for this agent because TaskList, TaskOutput, and TaskStop are not enabled.';
+
+const PARAMETERS_WITH_BACKGROUND = toInputJsonSchema(AskUserQuestionInputSchemaWithBackground);
+const PARAMETERS_FOREGROUND_ONLY = toInputJsonSchema(AskUserQuestionInputSchema);
+
 export class AskUserQuestionTool implements IAskUserQuestionTool {
   declare readonly _serviceBrand: undefined;
   readonly name = 'AskUserQuestion' as const;
-  readonly description: string;
-  readonly parameters: Record<string, unknown>;
 
   constructor(
     @ISessionQuestionService private readonly question: ISessionQuestionService,
     @ITelemetryService private readonly telemetry: ITelemetryService,
     @IAgentTaskService private readonly tasks: IAgentTaskService,
     @IAgentScopeContext private readonly scopeContext: IAgentScopeContext,
-  ) {
-    this.description = `${DESCRIPTION}- Set background=true when you can keep working without the answer. This starts a background question task and returns a task_id immediately. The answer arrives automatically in a later turn — you do not need to poll, sleep, or check on it. Continue with other work; never fabricate or predict the answer.`;
-    this.parameters = toInputJsonSchema(this.inputSchema());
+    @IAgentToolPolicyService private readonly toolPolicy: IAgentToolPolicyService,
+  ) {}
+
+  get description(): string {
+    return `${DESCRIPTION}${this.allowBackground() ? BACKGROUND_DESCRIPTION : ''}`;
+  }
+
+  get parameters(): Record<string, unknown> {
+    return this.allowBackground() ? PARAMETERS_WITH_BACKGROUND : PARAMETERS_FOREGROUND_ONLY;
   }
 
   resolveExecution(args: AskUserQuestionInput): ToolExecution {
@@ -67,6 +80,10 @@ export class AskUserQuestionTool implements IAskUserQuestionTool {
     args: AskUserQuestionInput,
     { toolCallId, signal, turnId, trace }: ExecutableToolContext,
   ): Promise<ExecutableToolResult> {
+    if (args.background === true && !this.allowBackground()) {
+      return { isError: true, output: BACKGROUND_UNAVAILABLE_MESSAGE };
+    }
+
     const uniquenessError = questionUniquenessError(args.questions);
     if (uniquenessError !== null) {
       return { isError: true, output: uniquenessError };
@@ -79,8 +96,12 @@ export class AskUserQuestionTool implements IAskUserQuestionTool {
     return this.executeQuestion(args, { toolCallId, turnId, signal, trace });
   }
 
-  private inputSchema(): z.ZodType<AskUserQuestionInput> {
-    return AskUserQuestionInputSchemaWithBackground;
+  private allowBackground(): boolean {
+    return (
+      this.toolPolicy.isToolActive('TaskList') &&
+      this.toolPolicy.isToolActive('TaskOutput') &&
+      this.toolPolicy.isToolActive('TaskStop')
+    );
   }
 
   private executeInBackground(

packages/agent-core-v2/test/agent/questionTools/tools/ask-user.test.ts

@@ -1,24 +1,34 @@
-import { describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
+import { DisposableStore } from '#/_base/di/lifecycle';
+import { createServices } from '#/_base/di/test';
 import { CoreErrors } from '#/_base/errors/codes';
 import { Error2 } from '#/_base/errors/errors';
 import {
   AskUserQuestionInputSchema,
+  IAskUserQuestionTool,
   type AskUserQuestionInput,
 } from '#/agent/tools/ask-user-question/ask-user-question';
 import { AskUserQuestionTool } from '#/agent/tools/ask-user-question/askUserQuestionTool';
 import { ITelemetryService } from '#/app/telemetry/telemetry';
 import { IAgentTaskService } from '#/agent/task/task';
 import { IAgentScopeContext } from '#/agent/scopeContext/scopeContext';
-import type {
+import { IAgentToolPolicyService } from '#/agent/toolPolicy/toolPolicy';
+import {
   ISessionQuestionService,
-  QuestionRequest,
-  QuestionResult,
+  type QuestionRequest,
+  type QuestionResult,
 } from '#/session/question/question';
-import type { QuestionBackgroundTask } from '#/agent/tools/ask-user-question/question-background-task';
+import type {
+  QuestionBackgroundTask,
+  QuestionTaskInfo,
+} from '#/agent/tools/ask-user-question/question-background-task';
 import { executeTool } from '../../../tools/fixtures/execute-tool';
 
 const signal = new AbortController().signal;
+const TASK_TOOLS = new Set(['TaskList', 'TaskOutput', 'TaskStop']);
+
+let disposables: DisposableStore;
 
 function input(
   overrides: Partial<AskUserQuestionInput['questions'][number]> = {},
@@ -41,13 +51,14 @@ function input(
 
 function makeTool(
   options: {
+    readonly activeTaskTools?: ReadonlySet<string>;
     readonly request?: (
       req: QuestionRequest,
       requestOptions?: { readonly signal?: AbortSignal },
     ) => Promise<QuestionResult>;
   } = {},
 ): {
-  readonly tool: AskUserQuestionTool;
+  readonly tool: IAskUserQuestionTool;
   readonly request: ReturnType<typeof vi.fn>;
   readonly telemetryTrack: ReturnType<typeof vi.fn>;
   readonly registerTask: ReturnType<typeof vi.fn>;
@@ -56,23 +67,54 @@ function makeTool(
 } {
   const request = vi.fn(options.request ?? (async () => ({ Postgres: true }) as QuestionResult));
   const telemetryTrack = vi.fn();
-  const question = { request } as unknown as ISessionQuestionService;
-  const telemetry = { track2: telemetryTrack } as unknown as ITelemetryService;
   let lastTask: QuestionBackgroundTask | undefined;
   const registerTask = vi.fn((task: QuestionBackgroundTask) => {
     lastTask = task;
     return 'q_test_task_id';
   });
-  const getTask = vi.fn((id: string) =>
-    id === 'q_test_task_id' ? { status: 'running' } : undefined,
+  const getTask = vi.fn(
+    (id: string): QuestionTaskInfo | undefined =>
+      id === 'q_test_task_id'
+        ? {
+            taskId: id,
+            description: 'Which database?',
+            status: 'running',
+            detached: true,
+            startedAt: 0,
+            endedAt: null,
+            kind: 'question',
+            questionCount: 1,
+            toolCallId: 'call_bg',
+          }
+        : undefined,
   );
-  const tasks = { registerTask, getTask } as unknown as IAgentTaskService;
-  const scopeContext = { agentId: 'main' } as unknown as IAgentScopeContext;
-  const tool = new AskUserQuestionTool(question, telemetry, tasks, scopeContext);
+  const activeTaskTools = options.activeTaskTools ?? TASK_TOOLS;
+  const ix = createServices(disposables, {
+    additionalServices: (reg) => {
+      reg.definePartialInstance(ISessionQuestionService, { request });
+      reg.definePartialInstance(ITelemetryService, { track2: telemetryTrack });
+      reg.definePartialInstance(IAgentTaskService, { registerTask, getTask });
+      reg.definePartialInstance(IAgentScopeContext, { agentId: 'main' });
+      reg.definePartialInstance(IAgentToolPolicyService, {
+        isToolActive: (name: string) => activeTaskTools.has(name),
+      });
+      reg.define(IAskUserQuestionTool, AskUserQuestionTool);
+    },
+    strict: true,
+  });
+  const tool = ix.get(IAskUserQuestionTool);
   return { tool, request, telemetryTrack, registerTask, getTask, lastRegisteredTask: () => lastTask };
 }
 
 describe('AskUserQuestionTool', () => {
+  beforeEach(() => {
+    disposables = new DisposableStore();
+  });
+
+  afterEach(() => {
+    disposables.dispose();
+  });
+
   it('exposes current metadata and schema', () => {
     const { tool } = makeTool();
 
@@ -167,14 +209,112 @@ describe('AskUserQuestionTool', () => {
     expect(request).toHaveBeenCalledOnce();
   });
 
-  it('builds the v1-aligned schema including an optional background flag', () => {
+  it('exposes background mode when all task controls are active', () => {
     const { tool } = makeTool();
     const params = tool.parameters as {
       properties: { background?: { type?: string; default?: boolean } };
     };
 
     expect(params.properties.background?.type).toBe('boolean');
     expect(params.properties.background?.default).toBe(false);
+    expect(tool.description).toContain('background=true');
+    expect(tool.description).toContain('task_id');
+  });
+
+  it('hides and rejects background mode after a task control becomes inactive', async () => {
+    const activeTaskTools = new Set(TASK_TOOLS);
+    const { tool, request, registerTask } = makeTool({
+      activeTaskTools,
+    });
+
+    expect(tool.parameters).toHaveProperty('properties.background');
+    activeTaskTools.delete('TaskStop');
+
+    const params = tool.parameters as { properties: Record<string, unknown> };
+
+    expect(params.properties).not.toHaveProperty('background');
+    expect(tool.description.toLowerCase()).not.toContain('background');
+    expect(tool.description).not.toContain('task_id');
+    expect(tool.description).not.toContain('TaskOutput');
+
+    const result = await executeTool(tool, {
+      turnId: 0,
+      toolCallId: 'call_bg_disabled',
+      args: { ...input(), background: true },
+      signal,
+    });
+
+    expect(result).toEqual({
+      isError: true,
+      output:
+        'Background questions are not available for this agent because TaskList, TaskOutput, and TaskStop are not enabled.',
+    });
+    expect(registerTask).not.toHaveBeenCalled();
+    expect(request).not.toHaveBeenCalled();
+  });
+
+  it('preserves foreground answers when background mode is unavailable', async () => {
+    const { tool, request } = makeTool({ activeTaskTools: new Set() });
+
+    const result = await executeTool(tool, {
+      turnId: 0,
+      toolCallId: 'call_fg_disabled',
+      args: input(),
+      signal,
+    });
+
+    expect(result).toEqual({
+      isError: false,
+      output: JSON.stringify({ answers: { Postgres: true } }),
+    });
+    expect(request).toHaveBeenCalledOnce();
+  });
+
+  it('preserves foreground dismissal when background mode is unavailable', async () => {
+    const { tool } = makeTool({
+      activeTaskTools: new Set(),
+      request: async () => null,
+    });
+
+    const result = await executeTool(tool, {
+      turnId: 0,
+      toolCallId: 'call_fg_dismissed',
+      args: input(),
+      signal,
+    });
+
+    expect(result).toEqual({
+      isError: false,
+      output: JSON.stringify({
+        answers: {},
+        note: 'User dismissed the question without answering.',
+      }),
+    });
+  });
+
+  it('preserves foreground errors when background mode is unavailable', async () => {
+    const { tool } = makeTool({
+      activeTaskTools: new Set(),
+      request: async () => {
+        throw new Error2(
+          CoreErrors.codes.NOT_IMPLEMENTED,
+          'Client does not support questions',
+        );
+      },
+    });
+
+    const result = await executeTool(tool, {
+      turnId: 0,
+      toolCallId: 'call_fg_unsupported',
+      args: input(),
+      signal,
+    });
+
+    expect(result).toEqual({
+      isError: true,
+      output:
+        'The connected client does not support interactive questions. Do NOT call this tool again. Ask the user directly in your text response instead.',
+    });
   });
 
   it('dispatches questions through the session question service', async () => {

packages/agent-core/src/agent/tool/index.ts

@@ -828,7 +828,8 @@ export class ToolManager {
         goalToolsEnabled && new b.GetGoalTool(this.agent),
         goalToolsEnabled && new b.SetGoalBudgetTool(this.agent),
         goalToolsEnabled && new b.UpdateGoalTool(this.agent),
-        this.agent.rpc?.requestQuestion && new b.AskUserQuestionTool(this.agent),
+        this.agent.rpc?.requestQuestion &&
+          new b.AskUserQuestionTool(this.agent, { allowBackground }),
         new b.TodoListTool(this.toolStore),
         new b.TaskListTool(background),
         new b.TaskOutputTool(background),

packages/agent-core/src/tools/builtin/collaboration/ask-user.ts

@@ -128,15 +128,27 @@ const QUESTION_DISMISSED_MESSAGE = 'User dismissed the question without answerin
 const QUESTION_UNSUPPORTED_FAILURE_MESSAGE =
   'The connected client does not support interactive questions. Do NOT call this tool again. Ask the user directly in your text response instead.';
 
+const BACKGROUND_DESCRIPTION =
+  '- Set background=true when you can keep working without the answer. This starts a background question task and returns a task_id immediately. The answer arrives automatically in a later turn — you do not need to poll, sleep, or check on it. Continue with other work; never fabricate or predict the answer.';
+
+const BACKGROUND_UNAVAILABLE_MESSAGE =
+  'Background questions are not available for this agent because TaskList, TaskOutput, and TaskStop are not enabled.';
+
 // ── Implementation ───────────────────────────────────────────────────
 
 export class AskUserQuestionTool implements BuiltinTool<AskUserQuestionInput> {
   readonly name = 'AskUserQuestion' as const;
   readonly description: string;
   readonly parameters: Record<string, unknown>;
 
-  constructor(private readonly agent: Agent) {
-    this.description = `${DESCRIPTION}- Set background=true when you can keep working without the answer. This starts a background question task and returns a task_id immediately. The answer arrives automatically in a later turn — you do not need to poll, sleep, or check on it. Continue with other work; never fabricate or predict the answer.`;
+  private readonly allowBackground: boolean;
+
+  constructor(
+    private readonly agent: Agent,
+    options?: { allowBackground?: boolean },
+  ) {
+    this.allowBackground = options?.allowBackground ?? true;
+    this.description = `${DESCRIPTION}${this.allowBackground ? BACKGROUND_DESCRIPTION : ''}`;
     this.parameters = toInputJsonSchema(this.inputSchema());
   }
 
@@ -160,6 +172,10 @@ export class AskUserQuestionTool implements BuiltinTool<AskUserQuestionInput> {
       turnId,
     }: ExecutableToolContext,
   ): Promise<ExecutableToolResult> {
+    if (args.background === true && !this.allowBackground) {
+      return { isError: true, output: BACKGROUND_UNAVAILABLE_MESSAGE };
+    }
+
     // AJV (the runtime arg validator) cannot express the uniqueness refine,
     // so enforce it here before any UI interaction or task registration.
     const uniquenessError = questionUniquenessError(args.questions);
@@ -175,7 +191,9 @@ export class AskUserQuestionTool implements BuiltinTool<AskUserQuestionInput> {
   }
 
   private inputSchema(): z.ZodType<AskUserQuestionInput> {
-    return AskUserQuestionInputSchemaWithBackground;
+    return this.allowBackground
+      ? AskUserQuestionInputSchemaWithBackground
+      : AskUserQuestionInputSchema;
   }
 
   private async executeQuestion(