fix(utils): contained ptree timeout rejections

- Observed timed-out child lifecycle failures without altering awaited rejection semantics.
- Added coverage for callers that settle without observing the lifecycle promise.

Fixes #6635

packages/utils/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Contained timed-out child lifecycle rejections so `ptree` callers cannot leak an unhandled `TimeoutError` after settling ([#6635](https://github.com/can1357/oh-my-pi/issues/6635)).
+
 ## [17.0.9] - 2026-07-23
 
 ### Breaking Changes

packages/utils/src/ptree.ts

@@ -309,6 +309,7 @@ export class ChildProcess<In extends InMask = InMask> {
 
 	attachTimeout(ms: number): void {
 		if (ms <= 0 || this.proc.killed) return;
+		this.#exited.catch(() => {});
 		Promise.race([
 			Bun.sleep(ms).then(() => true),
 			this.proc.exited.then(

packages/utils/test/ptree-timeout.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "bun:test";
+import { spawn, TimeoutError } from "@oh-my-pi/pi-utils/ptree";
+
+describe("ptree timeout", () => {
+	it("contains the lifecycle rejection when the caller does not observe exited", async () => {
+		const unhandled = new Set<unknown>();
+		const onUnhandled = (reason: unknown) => {
+			unhandled.add(reason);
+		};
+		process.on("unhandledRejection", onUnhandled);
+
+		try {
+			// Bun's subprocess timeout uses the platform clock; fake timers cannot drive this lifecycle.
+			using child = spawn(["bun", "-e", "Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0)"], {
+				timeout: 20,
+			});
+			await child.nothrow().text();
+			await child.proc.exited;
+			const nextTurn = Promise.withResolvers<void>();
+			setImmediate(nextTurn.resolve);
+			await nextTurn.promise;
+
+			expect(child.exitReason).toBeInstanceOf(TimeoutError);
+			expect(unhandled.has(child.exitReason)).toBe(false);
+		} finally {
+			process.off("unhandledRejection", onUnhandled);
+		}
+	});
+});