The agent loop writes an internal "(empty)" sentinel when the
nudge/prefill/empties/fallback ladder all fail. The gateway converts it
into a user-friendly notice at delivery, but the desktop group-chat
bridge appended the raw sentinel into the room log (seen posting
"(empty)" in a Bot Mode group room), and it synced to the shared
ui_meta for mobile.
Normalize at the single choke point, appendGroupChatEntry, mirroring
gateway/run.py substitution so group chat and gateway surfaces show the
same text. (pass)/empty silence semantics unchanged. Includes a
regression test proven to fail on the pre-fix code.
Fixes#94308
f05fec3565