The parent-chat suppression gate (afee35700e) keyed on evt task_id
starting with 'sa-'. But terminal_tool stamps ProcessSession.task_id
with the COLLAPSED container key from _resolve_container_task_id()
('default' or the session key — subagents intentionally share the
parent's container), so real child-spawned background processes carried
task_id='default' and their completion/watch notifications walked
straight past the gate into the parent conversation.
Fix: ProcessSession gains owner_task_id (the RAW spawning task id),
stamped by both spawn paths (spawn_local/spawn_via_env) from
terminal_tool's raw task_id, carried on every queued event
(completion, watch_match, watch_disabled, overflow), round-tripped
through the crash checkpoint, and used by both the drain suppression
gate and the attribution formatter (task_id remains the fallback so
synthetic/legacy events keep working).
Live repro: on origin/main a simulated subagent completion event with
the collapsed key was delivered to the parent drain (leak); on this
branch it is suppressed, parent-owned events still deliver, and
surface_child_process_notifications=true restores delivery with
attribution. 4 new regression tests fail on origin/main, pass here.
5a4dbdec27