test: validate sleep() works correctly inside loops

.changeset/add-sleep-in-loop-e2e-test.md

@@ -0,0 +1,5 @@
+---
+'@workflow/core': patch
+---
+
+Add e2e test validating that `sleep()` inside a loop with step calls correctly delays each iteration

packages/core/e2e/e2e.test.ts

@@ -1860,6 +1860,19 @@ describe('e2e', () => {
     }
   );
 
+  test(
+    'sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration',
+    { timeout: 60_000 },
+    async () => {
+      const run = await start(await e2e('sleepInLoopWorkflow'), []);
+      const returnValue = await run.returnValue;
+
+      // 3 iterations with 3s sleep between each pair = ~6s minimum total elapsed
+      expect(returnValue.timestamps).toHaveLength(3);
+      expect(returnValue.totalElapsed).toBeGreaterThan(5_000);
+    }
+  );
+
   test(
     'sleepWithSequentialStepsWorkflow - sequential steps work with concurrent sleep (control)',
     { timeout: 60_000 },

workbench/example/workflows/99_e2e.ts

@@ -1380,6 +1380,42 @@ async function addNumbers(a: number, b: number) {
   return a + b;
 }
 
+/**
+ * Validates that sleep() inside a loop with step calls actually delays
+ * execution on each iteration (i.e., sleeps are honored on replay, not skipped).
+ *
+ * Reproduces the scenario from a user report claiming that:
+ *   for (let i = 0; i < N; i++) {
+ *     await someStep();
+ *     await sleep(duration);
+ *   }
+ * ...fires all iterations instantly with zero delay.
+ */
+async function noopStep(iteration: number) {
+  'use step';
+  return { iteration, ts: Date.now() };
+}
+
+export async function sleepInLoopWorkflow() {
+  'use workflow';
+  const iterations = 3;
+  const sleepMs = 3_000; // 3s per iteration
+  const timestamps: number[] = [];
+
+  for (let i = 0; i < iterations; i++) {
+    const result = await noopStep(i);
+    timestamps.push(result.ts);
+    if (i < iterations - 1) {
+      await sleep(sleepMs);
+    }
+  }
+
+  const totalElapsed = timestamps[timestamps.length - 1] - timestamps[0];
+  return { timestamps, totalElapsed };
+}
+
+//////////////////////////////////////////////////////////
+
 /**
  * Control workflow: sleep + sequential steps (no hooks).
  * Proves that void sleep().then() does NOT interfere with sequential steps