Race condition: lastSentText was set synchronously before the async send/patch
completed, so a failed request was treated as delivered and subsequent ticks
skipped retrying. flushPendingPatch also didn't wait for in-flight interval ticks,
causing it to exit early (text === lastSentText guard) when a tick had just fired
but hadn't resolved yet, leaving streamMessageId null and forcing final delivery
to send a new post instead of patching the streamed one.
Fixes:
- schedulePatch interval: set lastSentText only after successful send/patch
- flushPendingPatch: wait up to 2s for in-flight patchSending before proceeding
- flushPendingPatch: set lastSentText after network success, not before
33678bb973