We have four or five pending and limbo queue implementations. Use a single pending queue instead. This should be simple FIFO streams (AtomicReadBuffer) accepting messages from various producers, and a single consumer should splat these messages into a database, where they can be indexed by gateway, status, timestamp, transaction ID, and anything else we find useful. Pending processing jobs should operate on the database records and not couple to the queue.

See also T130897 and T130894.