fix: prevent issues with midnight and day recognition on dst kick in

apps/server/src/services/__tests__/timerUtils.test.ts

@@ -557,6 +557,36 @@ describe('hasCrossedMidnight()', () => {
     const time = (15 * MILLIS_PER_HOUR) as TimeOfDay; // 15:00
     expect(hasCrossedMidnight(time, time)).toBe(false);
   });
+
+  describe('DST transitions', () => {
+    it('returns false during DST fall back (~1h backward jump)', () => {
+      // During fall back, clock goes from 02:59 → 02:00 (1h backward)
+      const previous = (2 * MILLIS_PER_HOUR + 59 * MILLIS_PER_MINUTE) as TimeOfDay; // 02:59
+      const current = (2 * MILLIS_PER_HOUR) as TimeOfDay; // 02:00
+      expect(hasCrossedMidnight(previous, current)).toBe(false);
+    });
+
+    it('returns true at actual midnight (~23h backward jump)', () => {
+      // Actual midnight crossing: 23:59 → 00:01 (~23h58m backward)
+      const previous = (23 * MILLIS_PER_HOUR + 59 * MILLIS_PER_MINUTE) as TimeOfDay; // 23:59
+      const current = (1 * MILLIS_PER_MINUTE) as TimeOfDay; // 00:01
+      expect(hasCrossedMidnight(previous, current)).toBe(true);
+    });
+
+    it('returns false for small backward jumps near midnight boundary', () => {
+      // Edge case: 12h backward is NOT a midnight cross
+      const previous = (12 * MILLIS_PER_HOUR) as TimeOfDay; // 12:00
+      const current = (0 * MILLIS_PER_HOUR) as TimeOfDay; // 00:00
+      expect(hasCrossedMidnight(previous, current)).toBe(false);
+    });
+
+    it('returns true for backward jumps exceeding 12h', () => {
+      // 12h + 1ms backward IS a midnight cross
+      const previous = (12 * MILLIS_PER_HOUR + 1) as TimeOfDay; // 12:00:00.001
+      const current = (0 * MILLIS_PER_HOUR) as TimeOfDay; // 00:00
+      expect(hasCrossedMidnight(previous, current)).toBe(true);
+    });
+  });
 });
 
 describe('skippedOutOfEvent()', () => {

apps/server/src/services/timerUtils.ts

@@ -10,11 +10,12 @@ export const normaliseEndTime = (start: number, end: number) => (end < start ? e
 
 /**
  * Checks whether the local wall clock wrapped into a new day
- * This currently uses a simple wrap heuristic and is centralized
- * so day-boundary behavior can be evolved in one place later.
+ * Uses a threshold to distinguish midnight wrap (~23h backward jump)
+ * from DST fall back (~1h backward jump)
  */
 export function hasCrossedMidnight(previous: TimeOfDay, current: TimeOfDay): boolean {
-  return previous > current;
+  const backwardJump = previous - current;
+  return backwardJump > 12 * MILLIS_PER_HOUR;
 }
 
 /**