This is an intentionally defective event RSVP demo. Cancelling a confirmed registration leaves a seat empty instead of promoting the earliest waiting guest.

Trace the real cancellation flow and all callers. Reproduce the bug with a failing regression check, then fix the shared cause with the smallest complete change. Preserve queue order and event capacity; repeated cancellation must not promote an extra guest. Run the relevant tests and show the diff and results.

Do not commit, push, open a PR, or deploy yet. Stop after the local fix and checks so I can review and use native /handoff in this conversation.