P6.2: Peer discovery implementation verification notes

Document that peer discovery was already implemented in prior commits
(e6cdd05 and 26c9521). All required components are in place:
- Headless Service with Downward API env vars
- SRV-based peer discovery in peer_discovery.rs
- Background refresh loop in main.rs
- miroir_peer_pod_count metric in middleware.rs
- Verification script

Acceptance criteria require multi-pod K8s deployment testing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

notes/miroir-m9q.2.md

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+# P6.2 Peer Discovery Implementation Summary
+
+## Status: Already Implemented
+
+The peer discovery feature described in the task was already implemented in prior commits:
+- `e6cdd05` - P6.2: Fix peer discovery DNS SRV service name and add test
+- `26c9521` - P6.2: Fix peer discovery DNS SRV service name and add POD_IP
+
+## Implementation Checklist
+
+### Helm Chart
+- [x] `charts/miroir/templates/miroir-headless.yaml` - Headless Service with label selector
+- [x] `charts/miroir/templates/miroir-deployment.yaml` - Downward API env vars (POD_NAME, POD_NAMESPACE, POD_IP)
+- [x] `charts/miroir/templates/_helpers.tpl` - Auto-derived service_name default using `miroir.fullname`
+- [x] `charts/miroir/values.yaml` - peer_discovery config with auto-documented defaults
+
+### Rust Code
+- [x] `crates/miroir-core/src/peer_discovery.rs` - SRV lookup implementation with trust-dns-resolver
+- [x] `crates/miroir-core/src/config.rs` - PeerDiscoveryConfig struct
+- [x] `crates/miroir-proxy/src/main.rs` - Background refresh loop (every 15s by default)
+- [x] `crates/miroir-proxy/src/middleware.rs` - miroir_peer_pod_count metric
+
+### Verification
+- [x] `tests/verify_p6_2_peer_discovery.sh` - Verification script for metrics and env vars
+- [x] Unit tests in `peer_discovery.rs` - test_srv_target_pod_name_extraction, test_peer_set_empty, test_peer_set_with_peers
+
+## Acceptance Criteria
+
+The following acceptance criteria require a multi-pod Kubernetes deployment to verify:
+
+1. **3-pod deployment: each pod sees all 3 peer names within 30s of last pod ready**
+   - Requires real K8s cluster with 3-pod deployment
+   - Verification: Check logs for "peer discovery refresh completed" with peer_count=3
+
+2. **Scale 3→5: new peers discovered within refresh_interval_s × 2**
+   - Requires real K8s cluster with scale operation
+   - Verification: Scale deployment and observe peer_count update
+
+3. **Pod eviction: crashed pod drops from peer set within refresh_interval_s × 2**
+   - Requires real K8s cluster with pod deletion
+   - Verification: Delete pod and observe peer_count decrease
+
+4. **miroir_peer_pod_count gauge matches kube_deployment_status_replicas_ready**
+   - Requires real K8s cluster with Prometheus scraping
+   - Verification: Compare metrics endpoint with deployment status
+
+These are integration tests that should be run in a staging environment. The verification script covers local development smoke testing.
+
+## Notes
+
+- The SRV lookup uses `_http._tcp.<service>.<namespace>.svc.cluster.local` format
+- Pod names are extracted from the first component of SRV target FQDNs
+- The implementation uses the system DNS resolver configuration from /etc/resolv.conf
+- Transient double-work during the 15-second discovery window is acceptable per plan §14.5