feat(O12): Prometheus alerting rules for all SLOs

- 11 alert rules across 5 groups
- Availability: service down, DB down, embedding down
- Latency: ingest p95 > 5s, query p95 > 2s, embedding p95 > 10s
- Errors: ingest/query error rate > 10%, embedding failures
- Storage: pool exhausted, write errors
- Quality: relevance precision < 30%
- PrometheusRule CRD for kube-prometheus-stack

k8s/infra/prometheus-alerts.yaml

@@ -0,0 +1,130 @@
+# Prometheus alerting rules for Poimen Memory (O12)
+# Deploy: kubectl apply -f k8s/infra/prometheus-alerts.yaml
+apiVersion: monitoring.coreos.com/v1
+kind: PrometheusRule
+metadata:
+  name: poimen-memory-alerts
+  namespace: poimen
+  labels:
+    app: poimen-memory
+    prometheus: k8s
+    role: alert-rules
+spec:
+  groups:
+    - name: poimen-memory.availability
+      rules:
+        - alert: MemoryServiceDown
+          expr: up{job="poimen-memory"} == 0
+          for: 2m
+          labels:
+            severity: critical
+          annotations:
+            summary: "Poimen memory service is down"
+            description: "Memory service has been unreachable for > 2 minutes"
+
+        - alert: MemoryDBDown
+          expr: memory_dependency_db_up == 0
+          for: 1m
+          labels:
+            severity: critical
+          annotations:
+            summary: "Memory service cannot reach database"
+            description: "DB dependency health check failing for > 1 minute"
+
+        - alert: MemoryEmbeddingDown
+          expr: memory_dependency_embedding_up == 0
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Embedding service unreachable"
+            description: "Embedding dependency health check failing for > 5 minutes"
+
+    - name: poimen-memory.latency
+      rules:
+        - alert: MemoryIngestLatencyHigh
+          expr: histogram_quantile(0.95, rate(memory_ingest_duration_seconds_bucket[5m])) > 5
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Ingest p95 latency > 5s"
+            description: "95th percentile ingest latency is {{ $value }}s"
+
+        - alert: MemoryQueryLatencyHigh
+          expr: histogram_quantile(0.95, rate(memory_query_duration_seconds_bucket[5m])) > 2
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Query p95 latency > 2s"
+            description: "95th percentile query latency is {{ $value }}s"
+
+        - alert: MemoryEmbeddingLatencyHigh
+          expr: histogram_quantile(0.95, rate(memory_query_embedding_duration_seconds_bucket[5m])) > 10
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Embedding p95 latency > 10s"
+            description: "95th percentile embedding call latency is {{ $value }}s"
+
+    - name: poimen-memory.errors
+      rules:
+        - alert: MemoryIngestErrorRateHigh
+          expr: rate(memory_ingest_errors_total[5m]) / rate(memory_ingest_requests_total[5m]) > 0.1
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Ingest error rate > 10%"
+            description: "{{ $value | humanizePercentage }} of ingest requests are failing"
+
+        - alert: MemoryQueryErrorRateHigh
+          expr: rate(memory_query_errors_total[5m]) / rate(memory_query_requests_total[5m]) > 0.1
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Query error rate > 10%"
+            description: "{{ $value | humanizePercentage }} of query requests are failing"
+
+        - alert: MemoryEmbeddingFailureRate
+          expr: rate(memory_query_embedding_failures_total[5m]) > 0.5
+          for: 3m
+          labels:
+            severity: critical
+          annotations:
+            summary: "Embedding failures > 0.5/s"
+            description: "Embedding service failing at {{ $value }}/s — queries cannot embed"
+
+    - name: poimen-memory.storage
+      rules:
+        - alert: MemoryDBPoolExhausted
+          expr: memory_db_pool_idle == 0
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "DB connection pool exhausted"
+            description: "No idle DB connections for > 5 minutes"
+
+        - alert: MemoryWriteErrorsHigh
+          expr: rate(memory_write_errors_total[5m]) > 1
+          for: 5m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Write errors > 1/s"
+            description: "Database write errors at {{ $value }}/s"
+
+    - name: poimen-memory.quality
+      rules:
+        - alert: MemoryRelevanceLow
+          expr: memory_relevance_precision < 0.3
+          for: 15m
+          labels:
+            severity: warning
+          annotations:
+            summary: "Retrieval relevance precision < 30%"
+            description: "Relevance precision is {{ $value | humanizePercentage }}"