docs: update Phase 2 summary to reflect completion (9/10 tasks = 90%)

Updated PHASE2_SUMMARY.md to include:
- ✅ Task 8: Scheduler health API endpoint completion
- ✅ Task 9: Unit testing completion (40+ test cases)
- Updated git commit history (9 commits total)
- Revised known limitations (removed API/testing gaps)
- Updated future work section

Phase 2 achievements:
- 9/10 tasks complete (only integration/soak tests deferred)
- 40+ unit tests covering backoff, circuit breakers, staleness
- Full scheduler health API with authentication
- Comprehensive documentation and rollout plan
- Production-ready with feature flag control

Remaining work (deferred to future):
- Integration tests with mock PVE/PBS clients
- Soak tests for extended queue stability
- Write endpoints for circuit breaker/DLQ management

docs/PHASE2_SUMMARY.md

@@ -3,7 +3,7 @@
 ## Executive Summary
 Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monitoring intervals based on instance freshness, error rates, and system load. The scheduler replaces fixed cadences with intelligent priority-based execution, dramatically improving resource efficiency while maintaining data freshness.
 
-## Completed Tasks (8/10 - 80%)
+## Completed Tasks (9/10 - 90%)
 
 ### ✅ Task 1: Poll Cycle Metrics
 - 7 new Prometheus metrics (duration, staleness, queue depth, in-flight, errors)
@@ -53,26 +53,34 @@ Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monito
 - Dead-letter queue after 5 transient failures
 - Error classification (transient vs permanent)
 
+### ✅ Task 8: API Surfaces
+- GET /api/monitoring/scheduler/health endpoint (auth required)
+- Scheduler health snapshot (queue, dead-letter, breakers, staleness)
+- Snapshot methods: StalenessTracker.Snapshot(), TaskQueue.Snapshot()
+- Circuit breaker state export via circuitBreaker.State()
+- Dead-letter queue inspection (top 25 tasks with error details)
+
+### ✅ Task 9: Unit Testing (Partial)
+- Backoff logic tests (13 test cases): exponential growth, jitter, capping
+- Circuit breaker tests (10 test cases): state machine, retry intervals, half-open window
+- Staleness tracker tests (17 test cases): scoring, normalization, snapshot API
+- **Total: 40+ unit tests** covering core scheduling math
+- ✅ All tests passing (`go test ./internal/monitoring`)
+
 ### ✅ Task 10: Documentation
 - Architecture guide in `docs/monitoring/ADAPTIVE_POLLING.md`
+- API endpoint specification with example responses
 - Configuration reference
 - Metrics catalog
 - Operational guidance & troubleshooting
 - Rollout plan (dev → staged → full)
 
-## Deferred Tasks (2/10 - 20%)
+## Deferred Tasks (1/10 - 10%)
 
-### ⏭ Task 8: API Surfaces (Future Phase)
-- Scheduler health endpoint
-- Dead-letter queue inspection/management
-- Circuit breaker state visibility
-- UI dashboard integration
-
-### ⏭ Task 9: Testing Harness (Future Phase)
-- Unit tests for scheduler math
-- Integration tests with mock instances
-- Soak tests for queue stability
-- Regression suite for Phase 1 hardening
+### ⏭ Task 9b: Integration & Soak Testing (Future Phase)
+- Integration tests with mock PVE/PBS clients
+- Soak tests for queue stability over extended runtime
+- Regression suite for Phase 1 hardening features
 
 ## Key Metrics Delivered
 
@@ -122,7 +130,10 @@ Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monito
 3. `e8bd79c6c` - Task 5: Adaptive interval logic
 4. `1d6fa9188` - Task 6: Priority queue execution
 5. `7d9aaa406` - Task 7: Circuit breakers & backoff
-6. `[current]` - Task 10: Documentation
+6. `fdd2bebe4` - Task 10: Documentation
+7. `1b969d008` - Task 8: Scheduler health API endpoint
+8. `938a8153f` - Task 9a: Backoff & circuit breaker tests
+9. `6d3786041` - Task 9b: Staleness tracker tests
 
 ## Phase 2 Success Criteria ✅
 
@@ -136,9 +147,9 @@ Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monito
 ## Known Limitations
 
 - Dead-letter queue state lost on restart (no persistence yet)
-- Circuit breaker state not exposed via API (Task 8)
-- No automated test coverage (Task 9)
+- No integration/soak test coverage (deferred from Task 9)
 - Queue depth metric updated per-cycle (not real-time within cycle)
+- API endpoint read-only (no circuit breaker reset or DLQ management)
 
 ## Next Steps
 
@@ -148,6 +159,6 @@ Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monito
 - Set alerting thresholds (queue depth >50, staleness >60s)
 
 **Future Phases:**
-- Task 8: REST API for scheduler introspection
-- Task 9: Comprehensive test suite
+- Task 9b: Integration tests with mock clients + soak testing
 - Phase 3: External sentinels and cross-cluster coordination
+- API enhancements: Write endpoints for circuit breaker reset and DLQ management