diff --git a/packages/coding-agent/src/modes/print-mode.ts b/packages/coding-agent/src/modes/print-mode.ts
index 7c0efb10b..54425749e 100644
--- a/packages/coding-agent/src/modes/print-mode.ts
+++ b/packages/coding-agent/src/modes/print-mode.ts
@@ -99,15 +99,14 @@ export async function runPrintMode(session: AgentSession, options: PrintModeOpti
 	// tail before dispose/exit. Same truncation class as issue #5309 (issue #7635).
 	let stdoutTail: Promise<void> = Promise.resolve();
 	const writeStdoutLine = (text: string): void => {
-		stdoutTail = stdoutTail.then(
-			() =>
-				new Promise<void>(resolve => {
-					process.stdout.write(text, err => {
-						if (err) logger.warn("print-mode stdout write failed", { error: err.message });
-						resolve();
-					});
-				}),
-		);
+		stdoutTail = stdoutTail.then(() => {
+			const { promise, resolve, reject } = Promise.withResolvers<void>();
+			process.stdout.write(text, err => {
+				if (err) reject(err);
+				else resolve();
+			});
+			return promise;
+		});
 	};
 
 	// Emit session header for JSON mode
diff --git a/packages/coding-agent/test/print-mode-json-flush.test.ts b/packages/coding-agent/test/print-mode-json-flush.test.ts
index a21e8cd40..0e5d4d398 100644
--- a/packages/coding-agent/test/print-mode-json-flush.test.ts
+++ b/packages/coding-agent/test/print-mode-json-flush.test.ts
@@ -127,7 +127,9 @@ describe("print-mode JSON flush (#7635)", () => {
 		// them all. The pre-fix fire-and-forget path settles and disposes here;
 		// the fix must still be blocked on the undrained agent_end write.
 		await agentEndWriteIssued;
-		await new Promise<void>(resolve => setImmediate(resolve));
+		const { promise: nextTask, resolve: resolveNextTask } = Promise.withResolvers<void>();
+		setImmediate(resolveNextTask);
+		await nextTask;
 		expect(releaseAgentEnd).toBeDefined();
 		expect(settled).toBe(false);
 		expect(harness.disposed()).toBe(false);