refactor(planning): drop the unreachable late worker message guard

release() already clears the worker handlers, so the released checks
inside them could never run. The lifetime test now states what it
checks: no handler is left for late messages.

Refs #277

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/services/leave-planner-worker-lifetime.spec.ts

@@ -128,7 +128,7 @@ describe('worker job lifetime', () => {
 			expect(worker.onerror).toBeNull();
 		};
 
-		it('releases the worker once on success and ignores late messages', async () => {
+		it('releases the worker once on success and leaves no handler for late messages', async () => {
 			const job = await start({});
 			job.deliver();
 			expect(await job.succeeded).toBe(true);

src/app/services/leave-planner.service.ts

@@ -323,10 +323,10 @@ function startWorkerJob(
 	});
 	let released = false;
 	worker.onmessage = (event: MessageEvent<WorkerResponse>) => {
-		if (!released && event.data) onMessage(event.data);
+		if (event.data) onMessage(event.data);
 	};
 	worker.onerror = () => {
-		if (!released) onError();
+		onError();
 	};
 	latestWorkerCancels.add(supersede);
 	return {