X_FLIGHT_GATE_OVERLOADED
Means
a concurrency gate is at its ceiling and its queue is full
Typical cause
more callers asked for a bounded resource than flightGate({ maxConcurrent, maxQueued }) admits — argon2 hashes, a browser pool, any work whose cost is memory rather than CPU time. Past the queue bound the answer is a refusal and never a longer queue: an unbounded queue turns a load spike into a memory fault and answers it minutes late. meta carries active, queued, both bounds and retryAfterSeconds, so it is classified retry-after and @ultimat3/http renders the header from it
Fix
retry after the Retry-After header, or widen the ceiling at the flightGate({ maxConcurrent, maxQueued }) call site — only if the box has the capacity the extra slots buy