Alerts: confidence gate before any push, held alerts, release on corroboration (server-26#300)

No confidence field exists anywhere in scene/incident data, so the alerter
derives one: match weight (talkgroup 1.0, extracted tag 0.8, raw transcript
0.6) scaled down only when stt_confidence is under ALERT_STT_REFERENCE (0.3),
zero for not_speech. Below ALERT_MIN_CONFIDENCE, or high severity (term list,
or a major incident) without ALERT_CORROBORATION_MIN_CALLS calls or
ALERT_HIGH_SEVERITY_MIN_CONFIDENCE, the match is written to alert_holds
(no Firestore rule, admin-only GET /alerts/held) and logged instead of pushed.
A needs_corroboration hold is released when a later call brings its incident
to the call minimum; a rule pushed by that call supersedes its hold.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/app/routers/alerts.py

@@ -28,6 +28,27 @@ async def list_alerts(
     return await fstore.collection_list("alert_events", **filters)
 
 
+@router.get("/alerts/held")
+async def list_held_alerts(
+    status: Optional[str] = Query("held", description="held | released | superseded | rule_gone; empty = all"),
+    org_id: Optional[str] = Query(None, description="Platform-admin only — omit for every org."),
+    _: dict = Depends(require_admin_token),
+):
+    """
+    Rule matches the confidence gate kept from being pushed (server-26#300).
+    Admin-only: a held match is by definition one we do not trust enough to
+    show, so it does not belong on any customer surface (and alert_holds has
+    no Firestore rule, so the browser cannot read it directly either).
+    """
+    filters = {}
+    if status:
+        filters["status"] = status
+    if org_id:
+        filters["org_id"] = org_id
+    holds = await fstore.collection_list("alert_holds", **filters)
+    return sorted(holds, key=lambda h: h.get("triggered_at") or "", reverse=True)
+
+
 @router.post("/alerts/{alert_id}/acknowledge")
 async def acknowledge_alert(alert_id: str, decoded: dict = Depends(require_service_or_firebase_token)):
     doc = await fstore.doc_get("alert_events", alert_id)