When multiple m.replace edits arrive concurrently, getLastReplacement()
may block on decryption. If an older edit's decryption completes after a
newer edit has already been applied, the older async result overwrites
the target event with stale content.
Add a monotonic update counter (replacementUpdateId) and centralise all
replacement updates through updateTargetEventReplacement(). The method
captures the counter before awaiting and discards the result if a newer
update has started in the meantime.
This race is especially pronounced in encrypted rooms with rapid
streaming-style edits, where variable decryption timing causes
out-of-order promise resolution.
Bas Nijholt
0e659d294e