#42178 dropped every session-scoped gateway event that arrived without an
explicit session_id, to stop background activity attaching to the focused
chat. But the gateway already stamps background sessions with their own id, so
an unscoped message/reasoning/tool/prompt event can only be the focused turn's
own output. Dropping those swallowed the live answer — it reappeared only after
a transcript refetch (manual refresh).
Narrow the guard to subagent.* (the only genuinely background/async family);
everything else falls back to the active session as before.
6e7033bb4c