P6.2: Peer discovery implementation verification summary

Verify that peer discovery via headless Service + Downward API
is fully implemented per plan §14.5:

- Helm templates: miroir-headless.yaml with clusterIP: None,
  miroir-deployment.yaml with POD_NAME/POD_NAMESPACE/POD_IP
- Rust: peer_discovery.rs with SRV lookup, refresh loop in main.rs,
  miroir_peer_pod_count metric in middleware.rs
- Verification: verify_p6_2_peer_discovery.sh script

Acceptance tests require multi-pod Kubernetes deployment:
1. 3-pod deployment: each pod sees all 3 peer names within 30s
2. Scale 3→5: new peers discovered within refresh_interval_s × 2
3. Pod eviction: crashed pod drops from peer set within 30s
4. miroir_peer_pod_count matches kube_deployment_status_replicas_ready

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

notes/miroir-m9q.2-summary.md

@@ -0,0 +1,63 @@
+# P6.2 Peer Discovery Implementation Summary
+
+## Status: Complete ✓
+
+Peer discovery via headless Service + Downward API is fully implemented per plan §14.5.
+
+## Implementation Verified
+
+### Helm Templates
+- `charts/miroir/templates/miroir-headless.yaml`
+  - `clusterIP: None` for headless Service
+  - Label selector matches Deployment pods
+  - Service name: `{{ include "miroir.fullname" . }}-headless`
+
+- `charts/miroir/templates/miroir-deployment.yaml`
+  - `POD_NAME` from `metadata.name` via Downward API
+  - `POD_NAMESPACE` from `metadata.namespace` via Downward API
+  - `POD_IP` from `status.podIP` via Downward API
+
+- `charts/miroir/templates/_helpers.tpl` (line 181)
+  - Config injection: `service_name: {{ printf "%s-headless" (include "miroir.fullname" .) }}`
+  - Matches headless Service name exactly
+
+### Rust Code
+- `crates/miroir-core/src/peer_discovery.rs`
+  - `PeerSet` struct with `peers: Vec<PeerId>` and `refreshed_at: Instant`
+  - `PeerDiscovery::refresh()` for SRV lookup via trust-dns-resolver
+  - Feature flag: `peer-discovery` (enabled in miroir-proxy)
+
+- `crates/miroir-core/src/config.rs`
+  - `PeerDiscoveryConfig` struct with `service_name` and `refresh_interval_s`
+  - Defaults: `service_name: "miroir-headless"`, `refresh_interval_s: 15`
+
+- `crates/miroir-proxy/src/main.rs` (lines 79-91, 407-431)
+  - Creates `PeerDiscovery` instance when `POD_NAME != "unknown"`
+  - Background refresh loop runs every `refresh_interval_s` seconds
+  - Calls `metrics.set_peer_pod_count(count)` on successful refresh
+
+- `crates/miroir-proxy/src/middleware.rs`
+  - `miroir_peer_pod_count` gauge metric (line 824)
+  - `set_peer_pod_count(u64)` method (line 1582)
+
+### Verification
+- `tests/verify_p6_2_peer_discovery.sh`
+  - NixOS-compatible shebang: `#!/usr/bin/env bash`
+  - Checks for metric existence and env vars
+
+## Acceptance Criteria (Require Kubernetes Cluster)
+
+The following acceptance tests require a multi-pod Kubernetes deployment:
+
+1. **3-pod deployment**: Each pod sees all 3 peer names within 30s of last pod ready
+2. **Scale 3→5**: New peers discovered within `refresh_interval_s × 2` (30s)
+3. **Pod eviction**: Crashed pod drops from peer set within `refresh_interval_s × 2` (30s)
+4. **Metric verification**: `miroir_peer_pod_count` matches `kube_deployment_status_replicas_ready`
+
+## 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
+- `cf9ae11` - P6.2: Fix verification script shebang for NixOS compatibility
+- `7784076` - P6.2: Peer discovery implementation verification notes
+- `bddfeb3` - P6.2: Verify peer discovery implementation (plan §14.5)