fix(provider-utils): read offset-less event times in their own time zone

.changeset/local-event-times.md

@@ -0,0 +1,6 @@
+---
+'@cal-sdk/provider-utils': patch
+'@cal-sdk/mock': patch
+---
+
+Event times without an offset, such as `{ dateTime: '2026-11-09T10:00:00', timeZone: 'Europe/Berlin' }`, are read in their own time zone instead of the machine's. This fixes busy times, listing windows and recurrence expansion in the mock calendar.

packages/provider-utils/src/time/event-time.ts

@@ -10,11 +10,16 @@ export function isAllDay(time: EventTimeV1): time is Extract<EventTimeV1, { date
 /**
  * The instant an event time refers to, in epoch milliseconds.
  *
- * All-day dates have no instant of their own: they start at midnight in
- * `allDayTimeZone` (usually the calendar's zone), UTC when omitted.
+ * A `dateTime` without an offset is a wall-clock time in its `timeZone`, never in the
+ * zone of the machine running the code. All-day dates have no instant of their own:
+ * they start at midnight in `allDayTimeZone` (usually the calendar's zone), UTC when
+ * omitted.
  */
 export function eventTimeToInstant(time: EventTimeV1, allDayTimeZone = 'UTC'): number {
-  if (!isAllDay(time)) return Date.parse(time.dateTime);
+  if (!isAllDay(time)) {
+    const wallClock = parseLocalDateTime(time.dateTime);
+    return wallClock ? localToInstant(wallClock, time.timeZone) : Date.parse(time.dateTime);
+  }
   const local = parseLocalDateTime(time.date);
   if (!local) return Number.NaN;
   return localToInstant(local, allDayTimeZone);

packages/provider-utils/src/time/time.test.ts

@@ -115,6 +115,16 @@ describe('event time', () => {
     expect(eventTimeToInstant({ date: '2026-11-03' })).toBe(Date.parse('2026-11-03T00:00:00Z'));
   });
 
+  it('reads a date-time without an offset in its own time zone, not the host zone', () => {
+    expect(eventTimeToInstant({ dateTime: '2026-11-09T10:00:00', timeZone: 'Europe/Berlin' })).toBe(
+      Date.parse('2026-11-09T09:00:00Z'),
+    );
+    // Daylight saving time in New York.
+    expect(eventTimeToInstant({ dateTime: '2026-07-01T09:30', timeZone: 'America/New_York' })).toBe(
+      Date.parse('2026-07-01T13:30:00Z'),
+    );
+  });
+
   it('adds days across month and year ends', () => {
     expect(addDaysToDate('2026-12-31', 1)).toBe('2027-01-01');
     expect(addDaysToDate('2028-03-01', -1)).toBe('2028-02-29');