Complete a background subagent that settles after its turn

src/vs/platform/agentHost/node/claude/claudeSdkMessageRouter.ts

@@ -15,6 +15,7 @@ import { ISessionDatabase } from '../../common/sessionDataService.js';
 import { ClaudeFileEditObserver } from './claudeFileEditObserver.js';
 import { ClaudeMapperState, mapSDKMessageToAgentSignals } from './claudeMapSessionEvents.js';
 import type { SubagentRegistry } from './claudeSubagentRegistry.js';
+import { mapSubagentSystemMessage } from './claudeSubagentSignals.js';
 
 interface IClaudeSdkMessageContext {
 	readonly turnDuration?: number;
@@ -72,20 +73,27 @@ export class ClaudeSdkMessageRouter extends Disposable {
 			await this._editObserver.observeUser(message, turnId, this._mapperState);
 		}
 		if (turnId === undefined) {
+			// A background subagent settles with the queue already drained.
+			if (message.type === 'system') {
+				this._produceSignals(() => mapSubagentSystemMessage(message, this._chatChannelUri, this._subagents));
+			}
 			return;
 		}
+		this._produceSignals(() => mapSDKMessageToAgentSignals(
+			message,
+			this._chatChannelUri,
+			turnId,
+			this._mapperState,
+			this._logService,
+			this._subagents,
+			this._clientToolOwner,
+			context?.turnDuration,
+		));
+	}
+
+	private _produceSignals(map: () => readonly AgentSignal[]): void {
 		try {
-			const signals = mapSDKMessageToAgentSignals(
-				message,
-				this._chatChannelUri,
-				turnId,
-				this._mapperState,
-				this._logService,
-				this._subagents,
-				this._clientToolOwner,
-				context?.turnDuration,
-			);
-			for (const signal of signals) {
+			for (const signal of map()) {
 				this._onDidProduceSignal.fire(signal);
 			}
 		} catch (mapperErr) {

src/vs/platform/agentHost/test/node/claudeSdkMessageRouter.test.ts

@@ -40,6 +40,7 @@ interface IRouterHarness {
 	readonly router: ClaudeSdkMessageRouter;
 	readonly signals: AgentSignal[];
 	readonly fileService: FileService;
+	readonly subagents: SubagentRegistry;
 }
 
 class RecordingAgentEditAttributionService extends NullAgentEditAttributionService {
@@ -88,7 +89,7 @@ function createRouter(
 	));
 	const signals: AgentSignal[] = [];
 	disposables.add(router.onDidProduceSignal(s => signals.push(s)));
-	return { router, signals, fileService };
+	return { router, signals, fileService, subagents };
 }
 
 function assistantMessage(content: unknown): Extract<SDKMessage, { type: 'assistant' }> {
@@ -103,12 +104,30 @@ suite('ClaudeSdkMessageRouter', () => {
 
 	const disposables = ensureNoDisposablesAreLeakedInTestSuite();
 
-	test('handle with turnId=undefined produces no signals (turn-less messages are routed to nowhere)', async () => {
+	test('handle with turnId=undefined drops turn-scoped messages', async () => {
 		const { router, signals } = createRouter(disposables);
 		await router.handle(makeStreamEvent('sess-1', makeMessageStart()), undefined);
 		assert.deepStrictEqual(signals, []);
 	});
 
+	test('a background subagent that settles after its turn still completes', async () => {
+		const { router, signals, subagents } = createRouter(disposables);
+		subagents.recordSpawn('tu-1');
+		subagents.getSpawn('tu-1')!.background = true;
+
+		// The queue has drained by the time a background task notification
+		// arrives, so there is no turn id to scope it to.
+		await router.handle({
+			type: 'system',
+			subtype: 'task_notification',
+			tool_use_id: 'tu-1',
+			status: 'completed',
+		} as unknown as SDKMessage, undefined);
+
+		assert.deepStrictEqual(signals.map(s => s.kind), ['subagent_completed']);
+		assert.strictEqual(subagents.getSpawn('tu-1'), undefined);
+	});
+
 	test('handle with a turnId on a text content block produces ChatResponsePart + ChatDelta signals', async () => {
 		const { router, signals } = createRouter(disposables);
 		await router.handle(makeStreamEvent('sess-1', makeMessageStart()), 'turn-1');