Subagent activity UX. (#17570)

packages/core/src/agents/browser/browserAgentInvocation.ts

@@ -16,8 +16,11 @@
 
 import type { Config } from '../../config/config.js';
 import { LocalAgentExecutor } from '../local-executor.js';
-import type { AnsiOutput } from '../../utils/terminalSerializer.js';
-import { BaseToolInvocation, type ToolResult } from '../../tools/tools.js';
+import {
+  BaseToolInvocation,
+  type ToolResult,
+  type ToolLiveOutput,
+} from '../../tools/tools.js';
 import { ToolErrorType } from '../../tools/tool-error.js';
 import type { AgentInputs, SubagentActivityEvent } from '../types.js';
 import type { MessageBus } from '../../confirmation-bus/message-bus.js';
@@ -82,7 +85,7 @@ export class BrowserAgentInvocation extends BaseToolInvocation<
    */
   async execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
   ): Promise<ToolResult> {
     let browserManager;
 

packages/core/src/agents/local-executor.test.ts

@@ -711,25 +711,28 @@ describe('LocalAgentExecutor', () => {
         expect.arrayContaining([
           expect.objectContaining({
             type: 'THOUGHT_CHUNK',
-            data: { text: 'T1: Listing' },
+            data: expect.objectContaining({ text: 'T1: Listing' }),
           }),
           expect.objectContaining({
             type: 'TOOL_CALL_END',
-            data: { name: LS_TOOL_NAME, output: 'file1.txt' },
+            data: expect.objectContaining({
+              name: LS_TOOL_NAME,
+              output: 'file1.txt',
+            }),
           }),
           expect.objectContaining({
             type: 'TOOL_CALL_START',
-            data: {
+            data: expect.objectContaining({
               name: TASK_COMPLETE_TOOL_NAME,
               args: { finalResult: 'Found file1.txt' },
-            },
+            }),
           }),
           expect.objectContaining({
             type: 'TOOL_CALL_END',
-            data: {
+            data: expect.objectContaining({
               name: TASK_COMPLETE_TOOL_NAME,
               output: expect.stringContaining('Output submitted'),
-            },
+            }),
           }),
         ]),
       );

packages/core/src/agents/local-executor.ts

@@ -269,13 +269,22 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
       };
     }
 
-    const { nextMessage, submittedOutput, taskCompleted } =
+    const { nextMessage, submittedOutput, taskCompleted, aborted } =
       await this.processFunctionCalls(
         functionCalls,
         combinedSignal,
         promptId,
         onWaitingForConfirmation,
       );
+
+    if (aborted) {
+      return {
+        status: 'stop',
+        terminateReason: AgentTerminateMode.ABORTED,
+        finalResult: null,
+      };
+    }
+
     if (taskCompleted) {
       const finalResult = submittedOutput ?? 'Task completed successfully.';
       return {
@@ -857,6 +866,7 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
     nextMessage: Content;
     submittedOutput: string | null;
     taskCompleted: boolean;
+    aborted: boolean;
   }> {
     const allowedToolNames = new Set(this.toolRegistry.getAllToolNames());
     // Always allow the completion tool
@@ -864,6 +874,7 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
 
     let submittedOutput: string | null = null;
     let taskCompleted = false;
+    let aborted = false;
 
     // We'll separate complete_task from other tools
     const toolRequests: ToolCallRequestInfo[] = [];
@@ -878,8 +889,24 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
       // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
       const toolName = functionCall.name as string;
 
+      let displayName = toolName;
+      let description: string | undefined = undefined;
+
+      try {
+        const tool = this.toolRegistry.getTool(toolName);
+        if (tool) {
+          displayName = tool.displayName ?? toolName;
+          const invocation = tool.build(args);
+          description = invocation.getDescription();
+        }
+      } catch {
+        // Ignore errors during formatting for activity emission
+      }
+
       this.emitActivity('TOOL_CALL_START', {
         name: toolName,
+        displayName,
+        description,
         args,
       });
 
@@ -1077,8 +1104,9 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
           this.emitActivity('ERROR', {
             context: 'tool_call',
             name: toolName,
-            error: 'Tool call was cancelled.',
+            error: 'Request cancelled.',
           });
+          aborted = true;
         }
 
         // Add result to syncResults to preserve order later
@@ -1111,6 +1139,7 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
       nextMessage: { role: 'user', parts: toolResponseParts },
       submittedOutput,
       taskCompleted,
+      aborted,
     };
   }
 

packages/core/src/agents/local-invocation.test.ts

@@ -4,17 +4,25 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, it, expect, vi, beforeEach, type Mocked } from 'vitest';
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+  type Mocked,
+} from 'vitest';
 import type {
   LocalAgentDefinition,
   SubagentActivityEvent,
   AgentInputs,
+  SubagentProgress,
 } from './types.js';
 import { LocalSubagentInvocation } from './local-invocation.js';
 import { LocalAgentExecutor } from './local-executor.js';
 import { AgentTerminateMode } from './types.js';
 import { makeFakeConfig } from '../test-utils/config.js';
-import { ToolErrorType } from '../tools/tool-error.js';
 import type { Config } from '../config/config.js';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
 import { type z } from 'zod';
@@ -29,6 +37,7 @@ let mockConfig: Config;
 const testDefinition: LocalAgentDefinition<z.ZodUnknown> = {
   kind: 'local',
   name: 'MockAgent',
+  displayName: 'Mock Agent',
   description: 'A mock agent.',
   inputConfig: {
     inputSchema: {
@@ -70,6 +79,10 @@ describe('LocalSubagentInvocation', () => {
     );
   });
 
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
   it('should pass the messageBus to the parent constructor', () => {
     const params = { task: 'Analyze data' };
     const invocation = new LocalSubagentInvocation(
@@ -173,7 +186,12 @@ describe('LocalSubagentInvocation', () => {
         mockConfig,
         expect.any(Function),
       );
-      expect(updateOutput).toHaveBeenCalledWith('Subagent starting...\n');
+      expect(updateOutput).toHaveBeenCalledWith(
+        expect.objectContaining({
+          isSubagentProgress: true,
+          agentName: 'MockAgent',
+        }),
+      );
 
       expect(mockExecutorInstance.run).toHaveBeenCalledWith(params, signal);
 
@@ -211,13 +229,17 @@ describe('LocalSubagentInvocation', () => {
 
       await invocation.execute(signal, updateOutput);
 
-      expect(updateOutput).toHaveBeenCalledWith('Subagent starting...\n');
-      expect(updateOutput).toHaveBeenCalledWith('🤖💭 Analyzing...');
-      expect(updateOutput).toHaveBeenCalledWith('🤖💭  Still thinking.');
-      expect(updateOutput).toHaveBeenCalledTimes(3); // Initial message + 2 thoughts
+      expect(updateOutput).toHaveBeenCalledTimes(3); // Initial + 2 updates
+      const lastCall = updateOutput.mock.calls[2][0] as SubagentProgress;
+      expect(lastCall.recentActivity).toContainEqual(
+        expect.objectContaining({
+          type: 'thought',
+          content: 'Analyzing... Still thinking.',
+        }),
+      );
     });
 
-    it('should NOT stream other activities (e.g., TOOL_CALL_START, ERROR)', async () => {
+    it('should stream other activities (e.g., TOOL_CALL_START, ERROR)', async () => {
       mockExecutorInstance.run.mockImplementation(async () => {
         const onActivity = MockLocalAgentExecutor.create.mock.calls[0][2];
 
@@ -226,7 +248,7 @@ describe('LocalSubagentInvocation', () => {
             isSubagentActivityEvent: true,
             agentName: 'MockAgent',
             type: 'TOOL_CALL_START',
-            data: { name: 'ls' },
+            data: { name: 'ls', args: {} },
           } as SubagentActivityEvent);
           onActivity({
             isSubagentActivityEvent: true,
@@ -240,9 +262,15 @@ describe('LocalSubagentInvocation', () => {
 
       await invocation.execute(signal, updateOutput);
 
-      // Should only contain the initial "Subagent starting..." message
-      expect(updateOutput).toHaveBeenCalledTimes(1);
-      expect(updateOutput).toHaveBeenCalledWith('Subagent starting...\n');
+      expect(updateOutput).toHaveBeenCalledTimes(3);
+      const lastCall = updateOutput.mock.calls[2][0] as SubagentProgress;
+      expect(lastCall.recentActivity).toContainEqual(
+        expect.objectContaining({
+          type: 'thought',
+          content: 'Error: Failed',
+          status: 'error',
+        }),
+      );
     });
 
     it('should run successfully without an updateOutput callback', async () => {
@@ -272,16 +300,19 @@ describe('LocalSubagentInvocation', () => {
 
       const result = await invocation.execute(signal, updateOutput);
 
-      expect(result.error).toEqual({
-        message: error.message,
-        type: ToolErrorType.EXECUTION_FAILED,
-      });
-      expect(result.returnDisplay).toBe(
-        `Subagent Failed: MockAgent\nError: ${error.message}`,
-      );
+      expect(result.error).toBeUndefined();
       expect(result.llmContent).toBe(
         `Subagent 'MockAgent' failed. Error: ${error.message}`,
       );
+      const display = result.returnDisplay as SubagentProgress;
+      expect(display.isSubagentProgress).toBe(true);
+      expect(display.recentActivity).toContainEqual(
+        expect.objectContaining({
+          type: 'thought',
+          content: `Error: ${error.message}`,
+          status: 'error',
+        }),
+      );
     });
 
     it('should handle executor creation failure', async () => {
@@ -291,19 +322,21 @@ describe('LocalSubagentInvocation', () => {
       const result = await invocation.execute(signal, updateOutput);
 
       expect(mockExecutorInstance.run).not.toHaveBeenCalled();
-      expect(result.error).toEqual({
-        message: creationError.message,
-        type: ToolErrorType.EXECUTION_FAILED,
-      });
-      expect(result.returnDisplay).toContain(`Error: ${creationError.message}`);
+      expect(result.error).toBeUndefined();
+      expect(result.llmContent).toContain(creationError.message);
+
+      const display = result.returnDisplay as SubagentProgress;
+      expect(display.recentActivity).toContainEqual(
+        expect.objectContaining({
+          content: `Error: ${creationError.message}`,
+          status: 'error',
+        }),
+      );
     });
 
-    /**
-     * This test verifies that the AbortSignal is correctly propagated and
-     * that a rejection from the executor due to abortion is handled gracefully.
-     */
     it('should handle abortion signal during execution', async () => {
       const abortError = new Error('Aborted');
+      abortError.name = 'AbortError';
       mockExecutorInstance.run.mockRejectedValue(abortError);
 
       const controller = new AbortController();
@@ -312,14 +345,24 @@ describe('LocalSubagentInvocation', () => {
         updateOutput,
       );
       controller.abort();
-      const result = await executePromise;
+      await expect(executePromise).rejects.toThrow('Aborted');
 
       expect(mockExecutorInstance.run).toHaveBeenCalledWith(
         params,
         controller.signal,
       );
-      expect(result.error?.message).toBe('Aborted');
-      expect(result.error?.type).toBe(ToolErrorType.EXECUTION_FAILED);
+    });
+
+    it('should throw an error and bubble cancellation when execution returns ABORTED', async () => {
+      const mockOutput = {
+        result: 'Cancelled by user',
+        terminate_reason: AgentTerminateMode.ABORTED,
+      };
+      mockExecutorInstance.run.mockResolvedValue(mockOutput);
+
+      await expect(invocation.execute(signal, updateOutput)).rejects.toThrow(
+        'Operation cancelled by user',
+      );
     });
   });
 });

packages/core/src/agents/local-invocation.ts

@@ -6,18 +6,25 @@
 
 import type { Config } from '../config/config.js';
 import { LocalAgentExecutor } from './local-executor.js';
-import type { AnsiOutput } from '../utils/terminalSerializer.js';
-import { BaseToolInvocation, type ToolResult } from '../tools/tools.js';
-import { ToolErrorType } from '../tools/tool-error.js';
-import type {
-  LocalAgentDefinition,
-  AgentInputs,
-  SubagentActivityEvent,
+import {
+  BaseToolInvocation,
+  type ToolResult,
+  type ToolLiveOutput,
+} from '../tools/tools.js';
+import {
+  type LocalAgentDefinition,
+  type AgentInputs,
+  type SubagentActivityEvent,
+  type SubagentProgress,
+  type SubagentActivityItem,
+  AgentTerminateMode,
 } from './types.js';
+import { randomUUID } from 'node:crypto';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
 
 const INPUT_PREVIEW_MAX_LENGTH = 50;
 const DESCRIPTION_MAX_LENGTH = 200;
+const MAX_RECENT_ACTIVITY = 3;
 
 /**
  * Represents a validated, executable instance of a subagent tool.
@@ -81,11 +88,20 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
    */
   async execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
   ): Promise<ToolResult> {
+    let recentActivity: SubagentActivityItem[] = [];
+
     try {
       if (updateOutput) {
-        updateOutput('Subagent starting...\n');
+        // Send initial state
+        const initialProgress: SubagentProgress = {
+          isSubagentProgress: true,
+          agentName: this.definition.name,
+          recentActivity: [],
+          state: 'running',
+        };
+        updateOutput(initialProgress);
       }
 
       // Create an activity callback to bridge the executor's events to the
@@ -93,11 +109,114 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
       const onActivity = (activity: SubagentActivityEvent): void => {
         if (!updateOutput) return;
 
-        if (
-          activity.type === 'THOUGHT_CHUNK' &&
-          typeof activity.data['text'] === 'string'
-        ) {
-          updateOutput(`🤖💭 ${activity.data['text']}`);
+        let updated = false;
+
+        switch (activity.type) {
+          case 'THOUGHT_CHUNK': {
+            const text = String(activity.data['text']);
+            const lastItem = recentActivity[recentActivity.length - 1];
+            if (
+              lastItem &&
+              lastItem.type === 'thought' &&
+              lastItem.status === 'running'
+            ) {
+              lastItem.content += text;
+            } else {
+              recentActivity.push({
+                id: randomUUID(),
+                type: 'thought',
+                content: text,
+                status: 'running',
+              });
+            }
+            updated = true;
+            break;
+          }
+          case 'TOOL_CALL_START': {
+            const name = String(activity.data['name']);
+            const displayName = activity.data['displayName']
+              ? String(activity.data['displayName'])
+              : undefined;
+            const description = activity.data['description']
+              ? String(activity.data['description'])
+              : undefined;
+            const args = JSON.stringify(activity.data['args']);
+            recentActivity.push({
+              id: randomUUID(),
+              type: 'tool_call',
+              content: name,
+              displayName,
+              description,
+              args,
+              status: 'running',
+            });
+            updated = true;
+            break;
+          }
+          case 'TOOL_CALL_END': {
+            const name = String(activity.data['name']);
+            // Find the last running tool call with this name
+            for (let i = recentActivity.length - 1; i >= 0; i--) {
+              if (
+                recentActivity[i].type === 'tool_call' &&
+                recentActivity[i].content === name &&
+                recentActivity[i].status === 'running'
+              ) {
+                recentActivity[i].status = 'completed';
+                updated = true;
+                break;
+              }
+            }
+            break;
+          }
+          case 'ERROR': {
+            const error = String(activity.data['error']);
+            const isCancellation = error === 'Request cancelled.';
+            const toolName = activity.data['name']
+              ? String(activity.data['name'])
+              : undefined;
+
+            if (toolName && isCancellation) {
+              for (let i = recentActivity.length - 1; i >= 0; i--) {
+                if (
+                  recentActivity[i].type === 'tool_call' &&
+                  recentActivity[i].content === toolName &&
+                  recentActivity[i].status === 'running'
+                ) {
+                  recentActivity[i].status = 'cancelled';
+                  updated = true;
+                  break;
+                }
+              }
+            }
+
+            recentActivity.push({
+              id: randomUUID(),
+              type: 'thought', // Treat errors as thoughts for now, or add an error type
+              content: isCancellation ? error : `Error: ${error}`,
+              status: isCancellation ? 'cancelled' : 'error',
+            });
+            updated = true;
+            break;
+          }
+          default:
+            break;
+        }
+
+        if (updated) {
+          // Keep only the last N items
+          if (recentActivity.length > MAX_RECENT_ACTIVITY) {
+            recentActivity = recentActivity.slice(-MAX_RECENT_ACTIVITY);
+          }
+
+          const progress: SubagentProgress = {
+            isSubagentProgress: true,
+            agentName: this.definition.name,
+            recentActivity: [...recentActivity], // Copy to avoid mutation issues
+            state: 'running',
+          };
+
+          updateOutput(progress);
         }
       };
 
@@ -109,6 +228,23 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
 
       const output = await executor.run(this.params, signal);
 
+      if (output.terminate_reason === AgentTerminateMode.ABORTED) {
+        const progress: SubagentProgress = {
+          isSubagentProgress: true,
+          agentName: this.definition.name,
+          recentActivity: [...recentActivity],
+          state: 'cancelled',
+        };
+
+        if (updateOutput) {
+          updateOutput(progress);
+        }
+
+        const cancelError = new Error('Operation cancelled by user');
+        cancelError.name = 'AbortError';
+        throw cancelError;
+      }
+
       const resultContent = `Subagent '${this.definition.name}' finished.
 Termination Reason: ${output.terminate_reason}
 Result:
@@ -131,13 +267,55 @@ ${output.result}
       const errorMessage =
         error instanceof Error ? error.message : String(error);
 
+      const isAbort =
+        (error instanceof Error && error.name === 'AbortError') ||
+        errorMessage.includes('Aborted');
+
+      // Mark any running items as error/cancelled
+      for (const item of recentActivity) {
+        if (item.status === 'running') {
+          item.status = isAbort ? 'cancelled' : 'error';
+        }
+      }
+
+      // Ensure the error is reflected in the recent activity for display
+      // But only if it's NOT an abort, or if we want to show "Cancelled" as a thought
+      if (!isAbort) {
+        const lastActivity = recentActivity[recentActivity.length - 1];
+        if (!lastActivity || lastActivity.status !== 'error') {
+          recentActivity.push({
+            id: randomUUID(),
+            type: 'thought',
+            content: `Error: ${errorMessage}`,
+            status: 'error',
+          });
+          // Maintain size limit
+          if (recentActivity.length > MAX_RECENT_ACTIVITY) {
+            recentActivity = recentActivity.slice(-MAX_RECENT_ACTIVITY);
+          }
+        }
+      }
+
+      const progress: SubagentProgress = {
+        isSubagentProgress: true,
+        agentName: this.definition.name,
+        recentActivity: [...recentActivity],
+        state: isAbort ? 'cancelled' : 'error',
+      };
+
+      if (updateOutput) {
+        updateOutput(progress);
+      }
+
+      if (isAbort) {
+        throw error;
+      }
+
       return {
         llmContent: `Subagent '${this.definition.name}' failed. Error: ${errorMessage}`,
-        returnDisplay: `Subagent Failed: ${this.definition.name}\nError: ${errorMessage}`,
-        error: {
-          message: errorMessage,
-          type: ToolErrorType.EXECUTION_FAILED,
-        },
+        returnDisplay: progress,
+        // We omit the 'error' property so that the UI renders our rich returnDisplay
+        // instead of the raw error message. The llmContent still informs the agent of the failure.
       };
     }
   }

packages/core/src/agents/subagent-tool.test.ts

@@ -120,6 +120,16 @@ describe('SubAgentInvocation', () => {
     );
   });
 
+  it('should return the correct description', () => {
+    const tool = new SubagentTool(testDefinition, mockConfig, mockMessageBus);
+    const params = {};
+    // @ts-expect-error - accessing protected method for testing
+    const invocation = tool.createInvocation(params, mockMessageBus);
+    expect(invocation.getDescription()).toBe(
+      "Delegating to agent 'LocalAgent'",
+    );
+  });
+
   it('should delegate shouldConfirmExecute to the inner sub-invocation (remote)', async () => {
     const tool = new SubagentTool(
       testRemoteDefinition,

packages/core/src/agents/subagent-tool.ts

@@ -12,8 +12,8 @@ import {
   BaseToolInvocation,
   type ToolCallConfirmationDetails,
   isTool,
+  type ToolLiveOutput,
 } from '../tools/tools.js';
-import type { AnsiOutput } from '../utils/terminalSerializer.js';
 import type { Config } from '../config/config.js';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
 import type { AgentDefinition, AgentInputs } from './types.js';
@@ -155,7 +155,7 @@ class SubAgentInvocation extends BaseToolInvocation<AgentInputs, ToolResult> {
 
   async execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
   ): Promise<ToolResult> {
     const validationError = SchemaValidator.validate(
       this.definition.inputConfig.inputSchema,

packages/core/src/agents/types.ts

@@ -71,6 +71,32 @@ export interface SubagentActivityEvent {
   data: Record<string, unknown>;
 }
 
+export interface SubagentActivityItem {
+  id: string;
+  type: 'thought' | 'tool_call';
+  content: string;
+  displayName?: string;
+  description?: string;
+  args?: string;
+  status: 'running' | 'completed' | 'error' | 'cancelled';
+}
+
+export interface SubagentProgress {
+  isSubagentProgress: true;
+  agentName: string;
+  recentActivity: SubagentActivityItem[];
+  state?: 'running' | 'completed' | 'error' | 'cancelled';
+}
+
+export function isSubagentProgress(obj: unknown): obj is SubagentProgress {
+  return (
+    typeof obj === 'object' &&
+    obj !== null &&
+    'isSubagentProgress' in obj &&
+    obj.isSubagentProgress === true
+  );
+}
+
 /**
  * The base definition for an agent.
  * @template TOutput The specific Zod schema for the agent's final output object.

packages/core/src/core/coreToolHookTriggers.ts

@@ -10,10 +10,11 @@ import type {
   ToolResult,
   AnyDeclarativeTool,
   AnyToolInvocation,
+  ToolLiveOutput,
 } from '../tools/tools.js';
 import { ToolErrorType } from '../tools/tool-error.js';
 import { debugLogger } from '../utils/debugLogger.js';
-import type { AnsiOutput, ShellExecutionConfig } from '../index.js';
+import type { ShellExecutionConfig } from '../index.js';
 import { ShellToolInvocation } from '../tools/shell.js';
 import { DiscoveredMCPToolInvocation } from '../tools/mcp-tool.js';
 
@@ -71,7 +72,7 @@ export async function executeToolWithHooks(
   toolName: string,
   signal: AbortSignal,
   tool: AnyDeclarativeTool,
-  liveOutputCallback?: (outputChunk: string | AnsiOutput) => void,
+  liveOutputCallback?: (outputChunk: ToolLiveOutput) => void,
   shellExecutionConfig?: ShellExecutionConfig,
   setPidCallback?: (pid: number) => void,
   config?: Config,

packages/core/src/core/geminiChat.ts

@@ -189,11 +189,16 @@ export class InvalidStreamError extends Error {
   readonly type:
     | 'NO_FINISH_REASON'
     | 'NO_RESPONSE_TEXT'
-    | 'MALFORMED_FUNCTION_CALL';
+    | 'MALFORMED_FUNCTION_CALL'
+    | 'UNEXPECTED_TOOL_CALL';
 
   constructor(
     message: string,
-    type: 'NO_FINISH_REASON' | 'NO_RESPONSE_TEXT' | 'MALFORMED_FUNCTION_CALL',
+    type:
+      | 'NO_FINISH_REASON'
+      | 'NO_RESPONSE_TEXT'
+      | 'MALFORMED_FUNCTION_CALL'
+      | 'UNEXPECTED_TOOL_CALL',
   ) {
     super(message);
     this.name = 'InvalidStreamError';
@@ -935,6 +940,12 @@ export class GeminiChat {
           'MALFORMED_FUNCTION_CALL',
         );
       }
+      if (finishReason === FinishReason.UNEXPECTED_TOOL_CALL) {
+        throw new InvalidStreamError(
+          'Model stream ended with unexpected tool call.',
+          'UNEXPECTED_TOOL_CALL',
+        );
+      }
       if (!responseText) {
         throw new InvalidStreamError(
           'Model stream ended with empty response text.',

packages/core/src/scheduler/tool-executor.ts

@@ -9,7 +9,8 @@ import type {
   ToolCallResponseInfo,
   ToolResult,
   Config,
-  AnsiOutput,
+  ToolResultDisplay,
+  ToolLiveOutput,
 } from '../index.js';
 import {
   ToolErrorType,
@@ -45,7 +46,7 @@ import {
 export interface ToolExecutionContext {
   call: ToolCall;
   signal: AbortSignal;
-  outputUpdateHandler?: (callId: string, output: string | AnsiOutput) => void;
+  outputUpdateHandler?: (callId: string, output: ToolLiveOutput) => void;
   onUpdateToolCall: (updatedCall: ToolCall) => void;
 }
 
@@ -68,7 +69,7 @@ export class ToolExecutor {
     // Setup live output handling
     const liveOutputCallback =
       tool.canUpdateOutput && outputUpdateHandler
-        ? (outputChunk: string | AnsiOutput) => {
+        ? (outputChunk: ToolLiveOutput) => {
             outputUpdateHandler(callId, outputChunk);
           }
         : undefined;
@@ -134,6 +135,7 @@ export class ToolExecutor {
             completedToolCall = this.createCancelledResult(
               call,
               'User cancelled tool execution.',
+              toolResult.returnDisplay,
             );
           } else if (toolResult.error === undefined) {
             completedToolCall = await this.createSuccessResult(
@@ -155,7 +157,12 @@ export class ToolExecutor {
           }
         } catch (executionError: unknown) {
           spanMetadata.error = executionError;
-          if (signal.aborted) {
+          const isAbortError =
+            executionError instanceof Error &&
+            (executionError.name === 'AbortError' ||
+              executionError.message.includes('Operation cancelled by user'));
+
+          if (signal.aborted || isAbortError) {
             completedToolCall = this.createCancelledResult(
               call,
               'User cancelled tool execution.',
@@ -182,6 +189,7 @@ export class ToolExecutor {
   private createCancelledResult(
     call: ToolCall,
     reason: string,
+    resultDisplay?: ToolResultDisplay,
   ): CancelledToolCall {
     const errorMessage = `[Operation Cancelled] ${reason}`;
     const startTime = 'startTime' in call ? call.startTime : undefined;
@@ -206,7 +214,7 @@ export class ToolExecutor {
             },
           },
         ],
-        resultDisplay: undefined,
+        resultDisplay,
         error: undefined,
         errorType: undefined,
         contentLength: errorMessage.length,

packages/core/src/scheduler/types.ts

@@ -11,8 +11,8 @@ import type {
   ToolCallConfirmationDetails,
   ToolConfirmationOutcome,
   ToolResultDisplay,
+  ToolLiveOutput,
 } from '../tools/tools.js';
-import type { AnsiOutput } from '../utils/terminalSerializer.js';
 import type { ToolErrorType } from '../tools/tool-error.js';
 import type { SerializableConfirmationDetails } from '../confirmation-bus/types.js';
 import { type ApprovalMode } from '../policy/types.js';
@@ -125,7 +125,7 @@ export type ExecutingToolCall = {
   request: ToolCallRequestInfo;
   tool: AnyDeclarativeTool;
   invocation: AnyToolInvocation;
-  liveOutput?: string | AnsiOutput;
+  liveOutput?: ToolLiveOutput;
   progressMessage?: string;
   progressPercent?: number;
   progress?: number;
@@ -197,7 +197,7 @@ export type ConfirmHandler = (
 
 export type OutputUpdateHandler = (
   toolCallId: string,
-  outputChunk: string | AnsiOutput,
+  outputChunk: ToolLiveOutput,
 ) => void;
 
 export type AllToolCallsCompleteHandler = (

packages/core/src/tools/shell.ts

@@ -17,6 +17,7 @@ import type {
   ToolCallConfirmationDetails,
   ToolExecuteConfirmationDetails,
   PolicyUpdateOptions,
+  ToolLiveOutput,
 } from './tools.js';
 import {
   BaseDeclarativeTool,
@@ -149,7 +150,7 @@ export class ShellToolInvocation extends BaseToolInvocation<
 
   async execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
     shellExecutionConfig?: ShellExecutionConfig,
     setPidCallback?: (pid: number) => void,
   ): Promise<ToolResult> {

packages/core/src/tools/tools.ts

@@ -19,6 +19,7 @@ import {
   type Question,
 } from '../confirmation-bus/types.js';
 import { type ApprovalMode } from '../policy/types.js';
+import type { SubagentProgress } from '../agents/types.js';
 
 /**
  * Represents a validated and ready-to-execute tool call.
@@ -64,7 +65,7 @@ export interface ToolInvocation<
    */
   execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
     shellExecutionConfig?: ShellExecutionConfig,
   ): Promise<TResult>;
 }
@@ -276,7 +277,7 @@ export abstract class BaseToolInvocation<
 
   abstract execute(
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
     shellExecutionConfig?: ShellExecutionConfig,
   ): Promise<TResult>;
 }
@@ -422,7 +423,7 @@ export abstract class DeclarativeTool<
   async buildAndExecute(
     params: TParams,
     signal: AbortSignal,
-    updateOutput?: (output: string | AnsiOutput) => void,
+    updateOutput?: (output: ToolLiveOutput) => void,
     shellExecutionConfig?: ShellExecutionConfig,
   ): Promise<TResult> {
     const invocation = this.build(params);
@@ -688,7 +689,14 @@ export interface TodoList {
   todos: Todo[];
 }
 
-export type ToolResultDisplay = string | FileDiff | AnsiOutput | TodoList;
+export type ToolLiveOutput = string | AnsiOutput | SubagentProgress;
+
+export type ToolResultDisplay =
+  | string
+  | FileDiff
+  | AnsiOutput
+  | TodoList
+  | SubagentProgress;
 
 export type TodoStatus = 'pending' | 'in_progress' | 'completed' | 'cancelled';
 

packages/core/src/utils/tool-utils.test.ts

@@ -98,6 +98,17 @@ describe('shouldHideToolCall', () => {
       ).toBe(!visible);
     },
   );
+
+  it('hides tool calls with a parentCallId', () => {
+    expect(
+      shouldHideToolCall({
+        displayName: 'any_tool',
+        status: CoreToolCallStatus.Success,
+        hasResultDisplay: true,
+        parentCallId: 'some-parent',
+      }),
+    ).toBe(true);
+  });
 });
 
 describe('getToolSuggestion', () => {

packages/core/src/utils/tool-utils.ts

@@ -28,20 +28,28 @@ export interface ShouldHideToolCallParams {
   approvalMode?: ApprovalMode;
   /** Whether the tool has produced a result for display. */
   hasResultDisplay: boolean;
+  /** The ID of the parent tool call, if any. */
+  parentCallId?: string;
 }
 
 /**
  * Determines if a tool call should be hidden from the standard tool history UI.
  *
  * We hide tools in several cases:
- * 1. Ask User tools that are in progress, displayed via specialized UI.
- * 2. Ask User tools that errored without result display, typically param
+ * 1. Tool calls that have a parent, as they are "internal" to another tool (e.g. subagent).
+ * 2. Ask User tools that are in progress, displayed via specialized UI.
+ * 3. Ask User tools that errored without result display, typically param
  *    validation errors that the agent automatically recovers from.
- * 3. WriteFile and Edit tools when in Plan Mode, redundant because the
+ * 4. WriteFile and Edit tools when in Plan Mode, redundant because the
  *    resulting plans are displayed separately upon exiting plan mode.
  */
 export function shouldHideToolCall(params: ShouldHideToolCallParams): boolean {
-  const { displayName, status, approvalMode, hasResultDisplay } = params;
+  const { displayName, status, approvalMode, hasResultDisplay, parentCallId } =
+    params;
+
+  if (parentCallId) {
+    return true;
+  }
 
   switch (displayName) {
     case ASK_USER_DISPLAY_NAME: