What does this PR do?

When a host reschedules a booking, this PR checks if any attendees (guests) are Cal.com users. If they are, their existing bookings are fetched as busy times and included in the available slots calculation — ensuring the host can only reschedule to times that work for both parties.

Problem

Currently, when a host reschedules, the system doesn’t check the guest’s availability. If the guest is a Cal.com user, this can result in scheduling conflicts.

Solution (minimal, focused changes)

1. UserRepository.findUsersByEmails() — Looks up Cal.com users by attendee emails
2. BookingRepository.findAcceptedBookingsByUserIdsOrEmails() — Fetches accepted bookings for those users within the date range
3. getUserAvailability — Accepts optional guestBusyTimes in initialData
4. slots/util.ts — Orchestrates the flow: when rescheduleUid is present, fetches guest busy times and passes them through

Design decisions

• Graceful degradation: If guest availability lookup fails, rescheduling still works (logged as warning)
• Only Cal.com users: Non-Cal.com guests are skipped (we cannot check their calendar)
• Excludes current booking: The booking being rescheduled is excluded from busy time calculation
• No UI changes: The existing reschedule UI automatically respects the filtered slots

Files changed (5 files)

• packages/features/users/repositories/UserRepository.ts
• packages/features/bookings/repositories/BookingRepository.ts
• packages/features/availability/lib/getUserAvailability.ts
• packages/trpc/server/routers/viewer/slots/util.ts
• apps/web/playwright/reschedule-guest-availability.e2e.ts

E2E coverage added

Added end-to-end coverage for host reschedule + guest availability in:

• apps/web/playwright/reschedule-guest-availability.e2e.ts

Scenarios covered:

1. Guest conflict blocks conflicting slots
2. All guests available allows successful reschedule
3. External (non-Cal.com) guest does not affect reschedule
4. Multiple guests (mixed Cal.com + external)
5. Original booking is excluded from self-conflict during reschedule

Visual demo

• Video: https://tmpfiles.org/24569580/2475bd22-f17d-42b4-a1d6-1383e26620d9.mov
• Direct download: https://tmpfiles.org/dl/24569580/2475bd22-f17d-42b4-a1d6-1383e26620d9.mov

/claim #16378

Fixes #16378