fix: add logging to silent error handlers, check maintenance windows for online events

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/observability.py

@@ -130,8 +130,8 @@ async def _check_nats(nats_url: str) -> dict:
         )
         try:
             await nc.drain()
-        except Exception:
-            pass
+        except Exception as exc:
+            logger.warning("Readiness check dependency failed: %s", exc)
         latency_ms = round((time.monotonic() - start) * 1000)
         return {"status": "up", "latency_ms": latency_ms, "error": None}
     except Exception as exc:

backend/app/services/alert_evaluator.py

@@ -696,6 +696,13 @@ async def evaluate_offline(device_id: str, tenant_id: str) -> None:
 
 async def evaluate_online(device_id: str, tenant_id: str) -> None:
     """Resolve offline alert when device comes back online."""
+    if await _is_device_in_maintenance(tenant_id, device_id):
+        logger.debug(
+            "Online event suppressed by maintenance window for device %s",
+            device_id,
+        )
+        return
+
     rule = await _get_offline_rule(tenant_id)
     rule_id = rule["id"] if rule else None
 

backend/app/services/config_diff_service.py

@@ -176,7 +176,7 @@ async def generate_and_store_diff(
                 },
             )
         except Exception:
-            pass
+            logger.warning("Config diff generation failed", exc_info=True)
 
         # 11. Parse structured changes (best-effort)
         try: