test(planning): make the checkpoint cancellation test deterministic

The cancelled stage takes about a millisecond, so under load the worker
could finish it before the cancel message arrived and report it as
completed. The real-worker harness now holds the worker after reporting
that stage until the cancel is delivered, keeping every assertion.

Refs #291

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

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

@@ -31,6 +31,7 @@ describe('real planning worker cancellation', () => {
 	let holdArtifacts = false;
 	const heldArtifactMessages: (() => void)[] = [];
 	let simulateLongCalculation = false;
+	let holdForCancelAtStage: string | undefined;
 	let simulatedElapsed = 0;
 	const threads = new Set<NodeWorker>();
 	const sentTypes: string[] = [];
@@ -43,8 +44,9 @@ describe('real planning worker cancellation', () => {
 		const entry = join(directory, 'entry.ts');
 		writeFileSync(
 			entry,
-			`import { parentPort, workerData } from 'node:worker_threads';
+			`import { parentPort, receiveMessageOnPort, workerData } from 'node:worker_threads';
 let elapsed = 0;
+const pause = new Int32Array(new SharedArrayBuffer(4));
 const originalNow = performance.now.bind(performance);
 if (workerData.simulateLongCalculation)
   Object.defineProperty(performance, 'now', { value: () => originalNow() + elapsed });
@@ -52,6 +54,16 @@ globalThis.self = { postMessage: (message) => {
   if (workerData.simulateLongCalculation && message.type === 'progress' && message.stage === 'optimization:default-unplaced-at-risk')
     setTimeout(() => { elapsed = 20_000; parentPort.postMessage({ type: 'test-clock', elapsed }); }, 0);
   parentPort.postMessage(message);
+  // The worker reads its queue only between event-loop turns, so a stage that is shorter than the
+  // host round trip finishes first. Hold the stage until the host's cancel arrives, then deliver it.
+  if (message.type === 'progress' && message.stage === workerData.holdForCancelAtStage) {
+    let next;
+    for (let waits = 0; !(next = receiveMessageOnPort(parentPort)); waits++) {
+      if (waits > 5000) throw new Error('The host never sent the cancel request.');
+      Atomics.wait(pause, 0, 0, 1);
+    }
+    globalThis.self.onmessage({ data: next.message });
+  }
 } };
 await import(${JSON.stringify(resolve('src/app/services/leave-planner.worker.ts'))});
 parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
@@ -73,6 +85,7 @@ parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 		localStorage.clear();
 		heartbeats = 0;
 		simulateLongCalculation = false;
+		holdForCancelAtStage = undefined;
 		simulatedElapsed = 0;
 		sentTypes.length = 0;
 		receivedTypes.length = 0;
@@ -80,7 +93,9 @@ parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 		class RealWorker {
 			onmessage: ((event: MessageEvent) => void) | null = null;
 			onerror: (() => void) | null = null;
-			private thread = new NodeWorker(bundle, { workerData: { simulateLongCalculation } });
+			private thread = new NodeWorker(bundle, {
+				workerData: { simulateLongCalculation, holdForCancelAtStage },
+			});
 			constructor() {
 				threads.add(this.thread);
 				this.thread.on('message', (data) => {
@@ -677,6 +692,8 @@ parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 	});
 
 	it('preserves balances and provenance after a valid checkpoint', async () => {
+		const cancelStage = 'optimization:default-non-working-day-gain';
+		holdForCancelAtStage = cancelStage;
 		const calculation = createPlanningCalculation({
 			horizon: { start: '2024-01-01', end: '2025-01-01' },
 			balances: [{ id: 'cp', type: 'cp', quantity: 3, expiryDate: '2024-12-31' }],
@@ -696,7 +713,7 @@ parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 				...presets.slice(1),
 			],
 			progress: (stage) => {
-				if (stage === 'optimization:default-non-working-day-gain') calculation.cancel();
+				if (stage === cancelStage) calculation.cancel();
 			},
 		});
 		const outcome = await calculation.outcome;
@@ -704,7 +721,7 @@ parentPort.on('message', (data) => globalThis.self.onmessage({ data }));
 		if (outcome.kind !== 'PlanningIncomplete') return;
 		expect(outcome.reasons[0].code).toBe('user-cancelled');
 		expect(outcome.completedStages).toContain('optimization:default-holiday-week-value');
-		expect(outcome.completedStages).not.toContain('optimization:default-non-working-day-gain');
+		expect(outcome.completedStages).not.toContain(cancelStage);
 		const incumbent = outcome.incumbent!;
 		expect(incumbent.placements).toHaveLength(3);
 		expect(incumbent.placements).toContainEqual({