M26: harden clean observability acceptance

backend/app/api/routers/observability.py

@@ -10,7 +10,7 @@ from sqlalchemy import func, select
 from app.core.config import get_settings
 from app.core.db import SessionLocal
 from app.core.observability import OUTBOX_EVENTS
-from app.models.outbox import DEMO_SCENARIO_ERROR_CODE, OutboxEvent
+from app.models.outbox import DELIVERY_STATUSES, DEMO_SCENARIO_ERROR_CODE, OutboxEvent
 
 router = APIRouter(tags=["observability"])
 settings = get_settings()
@@ -26,8 +26,14 @@ def _refresh_database_metrics() -> None:
             ).group_by(OutboxEvent.delivery_status, "demo")
         ).all()
     OUTBOX_EVENTS.clear()
+    # Keep every time series present even when a state currently contains no rows.
+    # Stable zero-valued series make dashboards and alerts deterministic after resets,
+    # restores and fresh installations instead of turning "zero" into "no data".
+    for scenario in ("synthetic", "operational"):
+        for status in DELIVERY_STATUSES:
+            OUTBOX_EVENTS.labels(scenario, status).set(0)
     for status, is_demo, count in rows:
-        OUTBOX_EVENTS.labels(str(status), "synthetic" if is_demo else "operational").set(count)
+        OUTBOX_EVENTS.labels("synthetic" if is_demo else "operational", str(status)).set(count)
 
 
 @router.get("/metrics", include_in_schema=False)