feat(core): Disable topic updates for subagents (#25567)

packages/core/src/agents/generalist-agent.ts

@@ -55,8 +55,9 @@ export const GeneralistAgent = (
     return {
       systemPrompt: getCoreSystemPrompt(
         context.config,
-        /*useMemory=*/ undefined,
+        /*userMemory=*/ undefined,
         /*interactiveOverride=*/ false,
+        /*topicUpdateNarrationOverride=*/ false,
       ),
       query: '${request}',
     };

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

@@ -82,6 +82,7 @@ import { CompleteTaskTool } from '../tools/complete-task.js';
 import {
   COMPLETE_TASK_TOOL_NAME,
   ACTIVATE_SKILL_TOOL_NAME,
+  UPDATE_TOPIC_TOOL_NAME,
 } from '../tools/definitions/base-declarations.js';
 
 /** A callback function to report on agent activity. */
@@ -189,6 +190,10 @@ export class LocalAgentExecutor<TOutput extends z.ZodTypeAny> {
         return;
       }
 
+      if (tool.name === UPDATE_TOPIC_TOOL_NAME) {
+        return;
+      }
+
       // Clone the tool, so it gets its own state and subagent messageBus
       const clonedTool = tool.clone(subagentMessageBus);
       agentToolRegistry.registerTool(clonedTool);

packages/core/src/core/prompts.ts

@@ -24,11 +24,13 @@ export function getCoreSystemPrompt(
   config: Config,
   userMemory?: string | HierarchicalMemory,
   interactiveOverride?: boolean,
+  topicUpdateNarrationOverride?: boolean,
 ): string {
   return new PromptProvider().getCoreSystemPrompt(
     config,
     userMemory,
     interactiveOverride,
+    topicUpdateNarrationOverride,
   );
 }
 

packages/core/src/prompts/promptProvider.test.ts

@@ -277,6 +277,56 @@ describe('PromptProvider', () => {
     });
   });
 
+  describe('topicUpdateNarrationOverride', () => {
+    let provider: PromptProvider;
+
+    beforeEach(() => {
+      provider = new PromptProvider();
+      mockConfig.topicState.reset();
+      (mockConfig.getToolRegistry as ReturnType<typeof vi.fn>).mockReturnValue({
+        getAllToolNames: vi.fn().mockReturnValue([UPDATE_TOPIC_TOOL_NAME]),
+      });
+      (mockConfig.getAgentRegistry as ReturnType<typeof vi.fn>).mockReturnValue(
+        {
+          getAllDefinitions: vi.fn().mockReturnValue([]),
+          getDefinition: vi.fn().mockReturnValue(undefined),
+        },
+      );
+    });
+
+    it('should disable topic update narration when override is false, even if config is true', () => {
+      vi.mocked(mockConfig.isTopicUpdateNarrationEnabled).mockReturnValue(true);
+
+      const prompt = provider.getCoreSystemPrompt(
+        mockConfig as unknown as Config,
+        /*userMemory=*/ undefined,
+        /*interactiveOverride=*/ undefined,
+        /*topicUpdateNarrationOverride=*/ false,
+      );
+
+      expect(prompt).not.toContain(
+        `As you work, the user follows along by reading topic updates that you publish with ${UPDATE_TOPIC_TOOL_NAME}.`,
+      );
+    });
+
+    it('should enable topic update narration when override is true, even if config is false', () => {
+      vi.mocked(mockConfig.isTopicUpdateNarrationEnabled).mockReturnValue(
+        false,
+      );
+
+      const prompt = provider.getCoreSystemPrompt(
+        mockConfig as unknown as Config,
+        /*userMemory=*/ undefined,
+        /*interactiveOverride=*/ undefined,
+        /*topicUpdateNarrationOverride=*/ true,
+      );
+
+      expect(prompt).toContain(
+        `As you work, the user follows along by reading topic updates that you publish with ${UPDATE_TOPIC_TOOL_NAME}.`,
+      );
+    });
+  });
+
   describe('Topic & Update Narration', () => {
     beforeEach(() => {
       mockConfig.topicState.reset();

packages/core/src/prompts/promptProvider.ts

@@ -44,6 +44,7 @@ export class PromptProvider {
     context: AgentLoopContext,
     userMemory?: string | HierarchicalMemory,
     interactiveOverride?: boolean,
+    topicUpdateNarrationOverride?: boolean,
   ): string {
     const systemMdResolution = resolvePathFromEnv(
       process.env['GEMINI_SYSTEM_MD'],
@@ -57,6 +58,10 @@ export class PromptProvider {
     const isYoloMode = approvalMode === ApprovalMode.YOLO;
     const skills = context.config.getSkillManager().getSkills();
     const toolNames = context.toolRegistry.getAllToolNames();
+    const isTopicUpdateNarrationEnabled =
+      topicUpdateNarrationOverride ??
+      context.config.isTopicUpdateNarrationEnabled();
+
     const enabledToolNames = new Set(toolNames);
 
     const approvedPlanPath = context.config.getApprovedPlanPath();
@@ -139,7 +144,7 @@ export class PromptProvider {
           hasSkills: skills.length > 0,
           hasHierarchicalMemory,
           contextFilenames,
-          topicUpdateNarration: context.config.isTopicUpdateNarrationEnabled(),
+          topicUpdateNarration: isTopicUpdateNarrationEnabled,
         })),
         subAgents: this.withSection(
           'agentContexts',
@@ -184,8 +189,7 @@ export class PromptProvider {
                 ? { path: approvedPlanPath }
                 : undefined,
               taskTracker: trackerDir,
-              topicUpdateNarration:
-                context.config.isTopicUpdateNarrationEnabled(),
+              topicUpdateNarration: isTopicUpdateNarrationEnabled,
             };
           },
           !isPlanMode,
@@ -207,8 +211,7 @@ export class PromptProvider {
             enableShellEfficiency:
               context.config.getEnableShellOutputEfficiency(),
             interactiveShellEnabled: context.config.isInteractiveShellEnabled(),
-            topicUpdateNarration:
-              context.config.isTopicUpdateNarrationEnabled(),
+            topicUpdateNarration: isTopicUpdateNarrationEnabled,
             memoryManagerEnabled: context.config.isMemoryManagerEnabled(),
           }),
         ),
@@ -251,7 +254,7 @@ export class PromptProvider {
     let sanitizedPrompt = finalPrompt.replace(/\n{3,}/g, '\n\n');
 
     // Context Reinjection (Active Topic)
-    if (context.config.isTopicUpdateNarrationEnabled()) {
+    if (isTopicUpdateNarrationEnabled) {
       const activeTopic = context.config.topicState.getTopic();
       if (activeTopic) {
         const sanitizedTopic = activeTopic