Stream Deliverable Events Multiplexed

Deliverable-scoped SSE — multiplexed across runs.

v1-beta-piping-backlog-remainder #29 Phase E step 29-21. Tails run_timeline_events filtered by deliverable_id only — no run_id filter. Frontend workspace subscribes once per deliverable and receives every event regardless of which run produced it:

• Digestion-run events (existing pipeline) — tagged with the active digestion run_id.
• Triage events (triage_started / triage_complete / triage_failed) emitted by JOB_TYPE_TRIAGE_SOURCE workers — tagged with a synthetic short-lived run_id per dispatch.

The frontend filters events by event_type + source_id to route to the right component (SourceStatusBadge, toast, Verifications tab). One SSE connection per workspace instead of one per source × run.

Companion to /{deliverable_id}/runs/{run_id}/timeline/stream which is per-run; use that when you specifically need a single run's events. This endpoint is the everything-bagel.