fix(session): skip queued /skill title starts while one is in flight

maybeStartTitleGeneration used to fire again for every untitled skill
prompt, so a queued /skill: during the first title request could race
and rename the session. Latch until the first request settles.

packages/coding-agent/src/session/agent-session.ts

@@ -535,6 +535,7 @@ export class AgentSession {
 	 *  the session cwd changes. */
 	#titleSystemPrompt: string | undefined;
 	#titleGenerationStart: (() => void) | undefined;
+	#titleGenerationInFlight = false;
 	#titleGenerationAbortController = new AbortController();
 	#toolChoiceQueue = new ToolChoiceQueue();
 
@@ -6549,10 +6550,22 @@ export class AgentSession {
 			this.#extensionRunner?.getCommand(
 				extensionCommandSpace === -1 ? firstMessage.slice(1) : firstMessage.slice(1, extensionCommandSpace),
 			) !== undefined;
-		if (isLocalExtensionCommand || this.sessionName || $env.PI_NO_TITLE || isLowSignalTitleInput(firstMessage)) {
+		if (
+			isLocalExtensionCommand ||
+			this.sessionName ||
+			this.#titleGenerationInFlight ||
+			$env.PI_NO_TITLE ||
+			isLowSignalTitleInput(firstMessage)
+		) {
 			return;
 		}
-		(onStart ?? this.#titleGenerationStart)?.();
+		this.#titleGenerationInFlight = true;
+		try {
+			(onStart ?? this.#titleGenerationStart)?.();
+		} catch (error) {
+			this.#titleGenerationInFlight = false;
+			throw error;
+		}
 		this.generateTitle(firstMessage)
 			.then(async title => {
 				// Re-check after generation so concurrent attempts cannot replace
@@ -6567,6 +6580,9 @@ export class AgentSession {
 					reason: "uncaught-auto-title-error",
 					error: err instanceof Error ? err.message : String(err),
 				});
+			})
+			.finally(() => {
+				this.#titleGenerationInFlight = false;
 			});
 	}
 

packages/coding-agent/test/agent-session-title-generation-dispose.test.ts

@@ -68,4 +68,42 @@ describe("AgentSession title generation disposal", () => {
 		expect(requestSignal?.aborted).toBe(true);
 		expect(await generation).toBeNull();
 	});
+
+	it("does not start a second auto-title request while the first is still in flight", async () => {
+		authStorage = await AuthStorage.create(":memory:");
+		authStorage.setRuntimeApiKey("anthropic", "test-key");
+		const model = getBundledModel("anthropic", "claude-sonnet-4-5");
+		if (!model) throw new Error("Expected claude-sonnet-4-5 model to exist");
+
+		const settings = Settings.isolated({
+			"compaction.enabled": false,
+			"providers.tinyModel": "online",
+		});
+		settings.overrideModelRoles({ smol: `${model.provider}/${model.id}` });
+		const agent = new Agent({
+			getApiKey: () => "test-key",
+			initialState: { model, systemPrompt: ["Test"], tools: [], messages: [] },
+			streamFn: createMockModel({ responses: [{ content: ["Done"] }] }).stream,
+		});
+		session = new AgentSession({
+			agent,
+			sessionManager: SessionManager.inMemory(),
+			settings,
+			modelRegistry: new ModelRegistry(authStorage),
+		});
+		const started = Promise.withResolvers<void>();
+		const response = Promise.withResolvers<ai.AssistantMessage>();
+		const completeSimple = vi.spyOn(ai, "completeSimple").mockImplementation(() => {
+			started.resolve();
+			return response.promise;
+		});
+
+		session.maybeStartTitleGeneration("/skill:implement issues/07-manual-llm.md");
+		await started.promise;
+		session.maybeStartTitleGeneration("/skill:implement issues/08-app-settings.md");
+		expect(completeSimple).toHaveBeenCalledTimes(1);
+
+		response.resolve(createAssistantMessage("<title>manual llm</title>"));
+		await response.promise;
+	});
 });