Two review findings on the salvage stack:
- _write_turns' _quietly consolidation keyed failure on a None result,
implicitly assuming add_memory never legitimately returns None. A None-
returning stub (the most common mock idiom) would mark every successful
write failed and re-append the batch forever. Module-level _FAILED
sentinel: only a raised exception re-queues.
- _pending_turns had no bound: a persistently failing service accumulated
one entry per turn for the process lifetime (gateway runs never
re-initialize), and every retry re-sent the whole accumulated payload —
O(n^2) upload bytes, and a size-rejected batch could never shrink. Cap
the buffer (50 turns / 256 KiB, drop oldest, warn once per trim).
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