Found via a new real end-to-end integration test (next commit), not by
inspection: a client that just called begin_queue() and receives the
server's first confirmation at the same revision (0) always treated
it as a conflict and requested a resync -- forever, since the resync
response is itself a same-revision confirmation hitting the exact same
false mismatch. A real Godot client against a real running server
would loop on GET /v1/queue/{id} without ever settling into QUEUED.
Root cause: apply_ticket_update()'s incoming_revision == revision
branch never adopts fields on acceptance, but _ticket_differs()
compared expires_at_unix -- a field begin_queue() has no way to set in
advance, since it doesn't know the server-assigned expiry yet. Every
first same-revision confirmation therefore looked like a conflict
unconditionally, not just occasionally.
Fix: exclude expires_at_unix from the conflict check (a differing
expiry at the same revision is expected, not a sign of corruption --
real conflicts are still caught via state/playlist), and adopt it on
acceptance so the field doesn't just become permanently stale instead.
The existing "same-revision conflict requests recovery" unit test
still passes unchanged: its fixture differs on `state`, not
expires_at_unix, so it was never actually exercising this bug.
Josh Creek