The AS, peer and prefix handlers wrote their batch to the database while
holding the mutex HandleMessage needs, and HandleMessage wrote a full batch
itself. For as long as a write took, the handler took nothing off its queue,
and the streamer dropped updates once the queue was half full.
Now only the flush goroutine writes: it takes the batch under the mutex,
releases it, then writes. A full batch wakes the flush goroutine instead.
Stop still writes what the handler holds.
While a write runs, the next batch has no size limit; the README memory
section says so.
Model: opus-5-5
sneak