test(06-02): add failing tests for RRULE UNTIL/COUNT + FREQ persistence

- vevent.test.ts: add COUNT, UNTIL-DATE, UNTIL-DATETIME serialization assertions
- outboxWorker.test.ts: add assembleRruleString (D-06) describe block (not yet exported)
- outboxWorker.test.ts: add FREQ persistence (D-07 regression) describe block
- RED: assembleRruleString not yet exported; FREQ-persistence cases fail on missing helper

apps/api/tests/broker/vevent.test.ts

@@ -90,6 +90,43 @@ describe('buildVeventString', () => {
     expect(result.icsString).not.toContain('RRULE:')
   })
 
+  // D-06: RRULE COUNT — verified ical.js 2.2.1 output
+  it('serializes COUNT in RRULE for a timed event (D-06)', () => {
+    const result = buildVeventString({
+      summary: 'Weekly',
+      allDay: false,
+      dtstart: new Date('2026-06-10T09:00:00Z'),
+      dtend: new Date('2026-06-10T10:00:00Z'),
+      rruleString: 'FREQ=WEEKLY;COUNT=5',
+    })
+    expect(result.icsString).toContain('RRULE:FREQ=WEEKLY;COUNT=5')
+  })
+
+  // D-06: RRULE UNTIL DATE form — all-day event must NOT contain T235959Z
+  it('serializes UNTIL as DATE form for all-day events (D-06)', () => {
+    const result = buildVeventString({
+      summary: 'Daily standup',
+      allDay: true,
+      dtstart: '2026-06-10',
+      dtend: '2026-06-11',
+      rruleString: 'FREQ=DAILY;UNTIL=20260630',
+    })
+    expect(result.icsString).toContain('RRULE:FREQ=DAILY;UNTIL=20260630')
+    expect(result.icsString).not.toContain('T235959Z')
+  })
+
+  // D-06: RRULE UNTIL DATETIME UTC form — timed event
+  it('serializes UNTIL as DATETIME UTC form for timed events (D-06)', () => {
+    const result = buildVeventString({
+      summary: 'Weekly',
+      allDay: false,
+      dtstart: new Date('2026-06-10T09:00:00Z'),
+      dtend: new Date('2026-06-10T10:00:00Z'),
+      rruleString: 'FREQ=WEEKLY;UNTIL=20260630T235959Z',
+    })
+    expect(result.icsString).toContain('RRULE:FREQ=WEEKLY;UNTIL=20260630T235959Z')
+  })
+
   it('uses the provided uid when given', () => {
     const uid = 'custom-uid-001@familysync'
     const result = buildVeventString({