feat(core): infrastructure for event-driven subagent history (#23914)

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

@@ -510,5 +510,36 @@ describe('LocalSubagentInvocation', () => {
         'Operation cancelled by user',
       );
     });
+
+    it('should publish SUBAGENT_ACTIVITY events to the MessageBus', async () => {
+      const { MessageBusType } = await import('../confirmation-bus/types.js');
+
+      mockExecutorInstance.run.mockImplementation(async () => {
+        const onActivity = MockLocalAgentExecutor.create.mock.calls[0][2];
+
+        if (onActivity) {
+          onActivity({
+            isSubagentActivityEvent: true,
+            agentName: 'MockAgent',
+            type: 'THOUGHT_CHUNK',
+            data: { text: 'Thinking...' },
+          } as SubagentActivityEvent);
+        }
+        return { result: 'Done', terminate_reason: AgentTerminateMode.GOAL };
+      });
+
+      await invocation.execute(signal, updateOutput);
+
+      expect(mockMessageBus.publish).toHaveBeenCalledWith(
+        expect.objectContaining({
+          type: MessageBusType.SUBAGENT_ACTIVITY,
+          subagentName: 'Mock Agent',
+          activity: expect.objectContaining({
+            type: 'thought',
+            content: 'Thinking...',
+          }),
+        }),
+      );
+    });
   });
 });

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

@@ -5,6 +5,7 @@
  */
 
 import { type AgentLoopContext } from '../config/agent-loop-context.js';
+import { MessageBusType } from '../confirmation-bus/types.js';
 import { LocalAgentExecutor } from './local-executor.js';
 import {
   BaseToolInvocation,
@@ -33,7 +34,6 @@ import {
 
 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.
@@ -87,6 +87,14 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
     return description.slice(0, DESCRIPTION_MAX_LENGTH);
   }
 
+  private publishActivity(activity: SubagentActivityItem): void {
+    void this.messageBus.publish({
+      type: MessageBusType.SUBAGENT_ACTIVITY,
+      subagentName: this.definition.displayName ?? this.definition.name,
+      activity,
+    });
+  }
+
   /**
    * Executes the subagent.
    *
@@ -99,7 +107,7 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
     signal: AbortSignal,
     updateOutput?: (output: ToolLiveOutput) => void,
   ): Promise<ToolResult> {
-    let recentActivity: SubagentActivityItem[] = [];
+    const recentActivity: SubagentActivityItem[] = [];
 
     try {
       if (updateOutput) {
@@ -140,6 +148,11 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
               });
             }
             updated = true;
+
+            const latestThought = recentActivity[recentActivity.length - 1];
+            if (latestThought) {
+              this.publishActivity(latestThought);
+            }
             break;
           }
           case 'TOOL_CALL_START': {
@@ -163,6 +176,11 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
               status: 'running',
             });
             updated = true;
+
+            const latestTool = recentActivity[recentActivity.length - 1];
+            if (latestTool) {
+              this.publishActivity(latestTool);
+            }
             break;
           }
           case 'TOOL_CALL_END': {
@@ -178,6 +196,8 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
               ) {
                 recentActivity[i].status = isError ? 'error' : 'completed';
                 updated = true;
+
+                this.publishActivity(recentActivity[i]);
                 break;
               }
             }
@@ -242,11 +262,6 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
         }
 
         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,
@@ -332,9 +347,7 @@ ${output.result}`;
             status: 'error',
           });
           // Maintain size limit
-          if (recentActivity.length > MAX_RECENT_ACTIVITY) {
-            recentActivity = recentActivity.slice(-MAX_RECENT_ACTIVITY);
-          }
+          // No limit on UI events sent via bus
         }
       }
 

packages/core/src/confirmation-bus/types.ts

@@ -12,6 +12,7 @@ import type {
 } from '../tools/tools.js';
 import type { ToolCall } from '../scheduler/types.js';
 import type { SandboxPermissions } from '../services/sandboxManager.js';
+import type { SubagentActivityItem } from '../agents/types.js';
 
 export enum MessageBusType {
   TOOL_CONFIRMATION_REQUEST = 'tool-confirmation-request',
@@ -23,6 +24,7 @@ export enum MessageBusType {
   TOOL_CALLS_UPDATE = 'tool-calls-update',
   ASK_USER_REQUEST = 'ask-user-request',
   ASK_USER_RESPONSE = 'ask-user-response',
+  SUBAGENT_ACTIVITY = 'subagent-activity',
 }
 
 export interface ToolCallsUpdateMessage {
@@ -207,6 +209,12 @@ export interface AskUserResponse {
   cancelled?: boolean;
 }
 
+export interface SubagentActivityMessage {
+  type: MessageBusType.SUBAGENT_ACTIVITY;
+  subagentName: string;
+  activity: SubagentActivityItem;
+}
+
 export type Message =
   | ToolConfirmationRequest
   | ToolConfirmationResponse
@@ -216,4 +224,5 @@ export type Message =
   | UpdatePolicy
   | AskUserRequest
   | AskUserResponse
-  | ToolCallsUpdateMessage;
+  | ToolCallsUpdateMessage
+  | SubagentActivityMessage;

packages/core/src/test-utils/mock-message-bus.ts

@@ -22,7 +22,7 @@ export class MockMessageBus {
   /**
    * Mock publish method that captures messages and simulates responses
    */
-  publish = vi.fn((message: Message) => {
+  publish = vi.fn(async (message: Message) => {
     this.publishedMessages.push(message);
 
     // Handle tool confirmation requests