Duplicate double bookings using recurring booking links

[JDO-AM]

ISSUE SUMMARY:

When using recurring booking links, users are able to create duplicate (double) bookings for the same slot. This occurs even when availability is correctly configured to prevent double booking.

WHY IS THIS CONSIDERED A BUG:

• Cal.com is expected to prevent overlapping bookings.
• Recurring links should respect the same logic as individual booking links.
• Users and clients should not be able to double-book a time slot once it’s taken.

ACTUAL RESULTS:

• The system allows two or more bookings for the same time slot, leading to scheduling conflicts and poor user experience.
• No conflict warning is triggered.
• Calendar reflects both events stacked on the same slot.

EXPECTED RESULTS:

• Once a slot is booked, it should become unavailable immediately for any future or repeat booking attempts — even via recurring booking links.
• Users attempting to book the same slot again should receive an error or be forced to select a different time.
• Booking logic should block overlaps by default, unless explicitly configured otherwise.

EVIDENCE:

• Calendar view showing two events at the same time
• Second booking shows event is in the past event if it's dated in the future.

[linear]

CAL-6171 Duplicate double bookings using recurring booking links

[naaa760]

Hi @JDO-AM
this PR adds database-level overlap checking to prevent race conditions that allowed double bookings with recurring links. The fix integrates conflict detection into both regular and recurring booking flows without breaking existing functionality.

[ibex088]

Hey Guys, we are working on a fix for this in recurring event V2.0

[idamayer]

I believe this is the issue I am also experiencing: note it is not a race condition. First event was booked weeks earlier - but did not conflict with the first session of the recurring booking. It appears the recurring booking did not check conflicts with any subsequent weeks.