fix(observability): preserve event names and escape metric labels

app/worker/metrics.py

@@ -3,6 +3,10 @@ from collections import defaultdict
 from typing import Any, Dict, List, Optional
 
 
+def escape_label(value: str) -> str:
+    return value.replace(chr(92), chr(92)*2).replace('"', chr(92)+'"').replace(chr(10), chr(92)+'n')
+
+
 class SimpleHistogram:
     """
     Lightweight, thread-safe Prometheus-compatible histogram.
@@ -136,13 +140,13 @@ class WorkerMetrics:
         lines.append("# TYPE cdr_processed_total counter")
         with self._lock:
             for (svc, rat), count in self._processed_total.items():
-                lines.append(f'cdr_processed_total{{service_type="{svc}",radio_access_type="{rat}"}} {count}')
+                lines.append(f'cdr_processed_total{{service_type="{escape_label(svc)}",radio_access_type="{escape_label(rat)}"}} {count}')
 
             # 2. cdr_dlq_total
             lines.append("# HELP cdr_dlq_total Total CDRs routed to DLQ by reason")
             lines.append("# TYPE cdr_dlq_total counter")
             for reason, count in self._dlq_total.items():
-                lines.append(f'cdr_dlq_total{{reason="{reason}"}} {count}')
+                lines.append(f'cdr_dlq_total{{reason="{escape_label(reason)}"}} {count}')
 
             # 3. Gauges
             lines.append("# HELP cdr_in_flight_buffer_size Current in-memory buffer size")