Upstream the 2026-07-09 live hot-fix from web1: send-message.sh used a fixed
tmux buffer name (__mosaic_send) shared by all concurrent senders on one
server — load-buffer overwrote load-buffer and paste-buffer -d deleted
underneath peers, cross-delivering or dropping messages. Bit the fleet during
the simultaneous restart (standing briefs swapped between sessions). Buffer
name is now unique per invocation (PID + nanoseconds).
Also brings auto-submit-drafts.sh (coordinator draft-flush watchdog, until now
only a loose file in the deployed ~/.config/mosaic/tools/tmux/) under source
control, and extends test-send-message-socket.sh with a concurrency lock:
5 parallel sends to distinct panes, asserting no drop and no cross-delivery.
The lock fails 3/3 runs against the pre-fix script and passes post-fix.
Without this, the next framework redeploy would regress the live fix.
