fix(coding-agent): prevented post-yield TUI stalls

Kept the Bun event loop live across subagent yield drains and delayed parent result flushes. Added a timer-lifecycle regression for the idle flush.

Fixes #8462

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed the parent TUI stalling after a subagent submits its result until terminal focus or resize wakes the event loop ([#8462](https://github.com/can1357/oh-my-pi/issues/8462)).
+
 ## [17.3.1] - 2026-08-13
 
 ### Fixed

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

@@ -37,6 +37,7 @@ import {
 	type AsideMessage,
 	type BeforeToolCallContext,
 	type BeforeToolCallResult,
+	EventLoopKeepalive,
 	resolveTelemetry,
 	type StreamFn,
 	TERMINAL_TOOL_RESULT_ABORT_REASON,
@@ -1213,15 +1214,28 @@ export class AgentSession {
 				}
 			},
 			scheduleIdleFlush: run => {
-				this.#schedulePostPromptTask(
-					async () => {
-						await run();
-					},
-					{
-						delayMs: 1,
-						onSkip: () => this.yieldQueue.cancelIdleFlushScheduling(),
-					},
-				);
+				const keepalive = new EventLoopKeepalive();
+				try {
+					this.#schedulePostPromptTask(
+						async () => {
+							try {
+								await run();
+							} finally {
+								keepalive[Symbol.dispose]();
+							}
+						},
+						{
+							delayMs: 1,
+							onSkip: () => {
+								keepalive[Symbol.dispose]();
+								this.yieldQueue.cancelIdleFlushScheduling();
+							},
+						},
+					);
+				} catch (error) {
+					keepalive[Symbol.dispose]();
+					throw error;
+				}
 			},
 		});
 		this.yieldQueue.register<LaunchCompletionEntry>(LAUNCH_COMPLETION_MESSAGE_TYPE, {

packages/coding-agent/src/task/executor.ts

@@ -6,7 +6,7 @@
 
 import path from "node:path";
 import type { AgentEvent, AgentIdentity, AgentMessage, AgentTelemetryConfig } from "@oh-my-pi/pi-agent-core";
-import { recordHandoff, resolveTelemetry } from "@oh-my-pi/pi-agent-core";
+import { EventLoopKeepalive, recordHandoff, resolveTelemetry } from "@oh-my-pi/pi-agent-core";
 import type { Api, Model, ServiceTierByFamily, Usage } from "@oh-my-pi/pi-ai";
 import { logger, popLoopPhase, prompt, pushLoopPhase, untilAborted } from "@oh-my-pi/pi-utils";
 import { ASYNC_JOB_MANAGER_SHUTDOWN_REASON, AsyncJobManager } from "../async";
@@ -1868,6 +1868,7 @@ async function driveSessionToYield(
 	monitor: SubagentRunMonitor,
 	task: string,
 ): Promise<DriveOutcome> {
+	using _keepalive = new EventLoopKeepalive();
 	const abortSignal = monitor.abortSignal;
 	let exitCode = 0;
 	let error: string | undefined;

packages/coding-agent/test/agent-session-async-delivery.test.ts

@@ -5,7 +5,7 @@
  * THAT session, and `hasPendingAsyncWork()` / `settleAsyncWork()` define the
  * run quiescence the task executor's barrier is built on.
  */
-import { afterEach, describe, expect, it } from "bun:test";
+import { afterEach, describe, expect, it, vi } from "bun:test";
 import { Agent } from "@oh-my-pi/pi-agent-core";
 import { createMockModel } from "@oh-my-pi/pi-ai/providers/mock";
 import { getBundledModel } from "@oh-my-pi/pi-catalog/models";
@@ -24,6 +24,7 @@ describe("AgentSession owner-routed async delivery", () => {
 	const authStorages: AuthStorage[] = [];
 
 	afterEach(async () => {
+		vi.useRealTimers();
 		if (session) {
 			await session.dispose();
 		}
@@ -343,4 +344,53 @@ describe("AgentSession owner-routed async delivery", () => {
 		await session.settleAsyncWork();
 		expect(session.hasPendingAsyncWork()).toBe(false);
 	});
+
+	it("keeps the event loop live until a delayed idle flush runs", async () => {
+		const model = getBundledModel("anthropic", "claude-sonnet-4-5")!;
+		const mock = createMockModel({ handler: () => ({ content: ["Done"] }) });
+		const agent = new Agent({
+			getApiKey: () => "test-key",
+			initialState: { model, systemPrompt: ["Test"], tools: [] },
+			convertToLlm,
+			streamFn: mock.stream,
+		});
+		const authStorage = await AuthStorage.create(":memory:");
+		authStorages.push(authStorage);
+		authStorage.setRuntimeApiKey("anthropic", "test-key");
+		const manager = new AsyncJobManager({});
+		AsyncJobManager.setInstance(manager);
+
+		session = new AgentSession({
+			agent,
+			sessionManager: SessionManager.inMemory(),
+			settings: Settings.isolated(),
+			modelRegistry: new ModelRegistry(authStorage),
+			agentId: "SubAgent",
+			asyncJobManager: manager,
+		});
+
+		let flushed = false;
+		session.yieldQueue.register("keepalive-probe", {
+			isStale: () => {
+				flushed = true;
+				return true;
+			},
+			build: () => null,
+		});
+		vi.useFakeTimers();
+		const baselineTimers = vi.getTimerCount();
+		session.yieldQueue.enqueue("keepalive-probe", {});
+
+		// The 1ms flush timer and a keepalive must both remain armed until the
+		// flush runs. Without the keepalive, Bun can park here until unrelated
+		// TTY I/O wakes the loop.
+		expect(vi.getTimerCount()).toBeGreaterThanOrEqual(baselineTimers + 2);
+
+		vi.advanceTimersByTime(1);
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		expect(flushed).toBe(true);
+		expect(vi.getTimerCount()).toBe(baselineTimers + 1);
+	});
 });