docs(bf-57ko1): add verification note

notes/bf-57ko1.md

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+# bf-57ko1 Verification Note
+
+## Summary
+Created `docs/operations/prometheus-rules.yaml` with 7 Prometheus alerting rules for pdftract serve deployments as specified in the plan Monitoring section (~line 3832).
+
+## Work Performed
+- Created `docs/operations/prometheus-rules.yaml` with:
+  - 5 required alerting rules as specified in bead description
+  - 2 additional alert rules recommended in the plan
+  - Proper Prometheus RuleGroups structure
+  - Alert annotations with runbook URLs pointing to plan.md
+
+## Alert Rules Implemented
+
+### Required Alerts (5)
+1. **PdftractExtractionLatencyHigh**: p99 > 300ms (2× 150ms target) for >5 minutes
+   - Severity: warning
+   - Expression: `histogram_quantile(0.99, ...) > 0.3`
+
+2. **PdftractErrorRateHigh**: HTTP 5xx rate > 1% over 5 minutes
+   - Severity: critical
+   - Expression: 5xx rate / total rate > 0.01
+
+3. **PdftractCacheHitRateLow**: Cache hit rate < 50%
+   - Severity: info
+   - Expression: hits / (hits + misses) < 0.5
+
+4. **PdftractWorkerSaturated**: Worker pool utilization > 80%
+   - Severity: warning
+   - Expression: `pdftract_rayon_pool_utilization > 0.8`
+
+5. **PdftractMemoryHigh**: RSS > 80% of max_decompress_bytes ceiling
+   - Severity: warning
+   - Expression: RSS / (max_bytes * 0.8) > 1
+
+### Additional Alerts (2)
+6. **PdftractCacheSizeGrowingUnchecked**: Cache growing > 1 GB/hour for 6 hours
+7. **PdftractDiagnosticFlood**: Error diagnostics > 10/sec
+
+## Acceptance Criteria Status
+- ✅ Valid Prometheus YAML structure (Prometheus RuleGroups format)
+- ✅ Contains 7 alerting rules (exceeds requirement of ≥5)
+- ✅ Runbook URLs point to docs/plan/plan.md monitoring section
+
+## Verification
+- File location: `docs/operations/prometheus-rules.yaml`
+- Commit: `f716d27a` - `docs(bf-57ko1): add Prometheus alerting rules for serve deployments`
+- Pushed to: `https://git.ardenone.com/jedarden/pdftract.git` (main branch)
+
+## Notes
+- promtool validation not performed (tool not available in environment)
+- YAML structure follows Prometheus RuleGroups specification
+- All alerts include proper severity labels, annotations, and runbook URLs
+- Alert expressions reference the metrics defined in the plan Monitoring section