emit_status_snapshot() now consults SFM /db/units (cached 15s) before
falling back to Emitter.last_seen for each seismograph. The fresher of
the two wins and the choice is recorded in a new per-unit
last_seen_source field ("sfm" | "heartbeat" | "none"). sfm_reachable is
exposed alongside so the UI can show degraded state.
Fallback is transparent: if SFM is unreachable or has no record for a
serial, the watcher heartbeat path takes over and the unit just shows
the HB badge instead of SFM. No schema changes; SLMs are untouched
(they don't go through SFM); modems inherit source from their pair.
active_table.html grows a small "SFM" / "HB" badge next to the age
column so operators can see at a glance which path is currently
driving each unit's status.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
serversdown
449e031589