fix(coding-agent): fix windows hanging when descendants inherit stdout/stderr handles (#2389)

packages/coding-agent/src/utils/child-process.ts

@@ -0,0 +1,86 @@
+import type { ChildProcess } from "node:child_process";
+
+const EXIT_STDIO_GRACE_MS = 100;
+
+/**
+ * Wait for a child process to terminate without hanging on inherited stdio handles.
+ *
+ * On Windows, daemonized descendants can inherit the child's stdout/stderr pipe
+ * handles. In that case the child emits `exit`, but `close` can hang forever even
+ * though the original process is already gone. We wait briefly for stdio to end,
+ * then forcibly stop tracking the inherited handles.
+ */
+export function waitForChildProcess(child: ChildProcess): Promise<number | null> {
+	return new Promise((resolve, reject) => {
+		let settled = false;
+		let exited = false;
+		let exitCode: number | null = null;
+		let postExitTimer: NodeJS.Timeout | undefined;
+		let stdoutEnded = child.stdout === null;
+		let stderrEnded = child.stderr === null;
+
+		const cleanup = () => {
+			if (postExitTimer) {
+				clearTimeout(postExitTimer);
+				postExitTimer = undefined;
+			}
+			child.removeListener("error", onError);
+			child.removeListener("exit", onExit);
+			child.removeListener("close", onClose);
+			child.stdout?.removeListener("end", onStdoutEnd);
+			child.stderr?.removeListener("end", onStderrEnd);
+		};
+
+		const finalize = (code: number | null) => {
+			if (settled) return;
+			settled = true;
+			cleanup();
+			child.stdout?.destroy();
+			child.stderr?.destroy();
+			resolve(code);
+		};
+
+		const maybeFinalizeAfterExit = () => {
+			if (!exited || settled) return;
+			if (stdoutEnded && stderrEnded) {
+				finalize(exitCode);
+			}
+		};
+
+		const onStdoutEnd = () => {
+			stdoutEnded = true;
+			maybeFinalizeAfterExit();
+		};
+
+		const onStderrEnd = () => {
+			stderrEnded = true;
+			maybeFinalizeAfterExit();
+		};
+
+		const onError = (err: Error) => {
+			if (settled) return;
+			settled = true;
+			cleanup();
+			reject(err);
+		};
+
+		const onExit = (code: number | null) => {
+			exited = true;
+			exitCode = code;
+			maybeFinalizeAfterExit();
+			if (!settled) {
+				postExitTimer = setTimeout(() => finalize(code), EXIT_STDIO_GRACE_MS);
+			}
+		};
+
+		const onClose = (code: number | null) => {
+			finalize(code);
+		};
+
+		child.stdout?.once("end", onStdoutEnd);
+		child.stderr?.once("end", onStderrEnd);
+		child.once("error", onError);
+		child.once("exit", onExit);
+		child.once("close", onClose);
+	});
+}