feat: round-5 abstractions — CircuitBreakerHealthCheck, TypedKeyRegistry, MetricsHttpHandler

.hermes/plans/mytheclipse-round5-spec.md

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+# Implementation Spec: Round 5
+
+## Status: COMPLETE
+
+## New Features
+
+### 1. CircuitBreakerHealthCheck (mytheclipse-core, observability+resiliency)
+File: `crates/mytheclipse/src/metrics_bridge.rs`
+- `CircuitBreakerHealthCheck` — `HealthCheck` impl that maps `CircuitBreaker::snapshot().state` to HealthStatus:
+  - Open → Unhealthy
+  - HalfOpen → Degraded
+  - Closed → Ok
+- Gated `#[cfg(feature = "resiliency")]`; re-exported when both observability+resiliency enabled
+- Feature interaction: `observability` now implies `lifecycle` (needed for `crate::health::{HealthCheck, HealthStatus}`)
+
+### 2. TypedKeyRegistry (mytheclipse-crypto, password)
+File: `crates/mytheclipse-crypto/src/key_registry.rs`
+- `TypedKeyRegistry<K, V>` — registry keyed by string ID, wraps KeyRing for current/previous rotation
+- `key_for(&self, id: &str) -> Option<&K>` typed lookup
+- `rotate_with_id(&mut self, id, key)` + `revoke(id)`
+- Default impl uses String keys (v4 signers)
+
+### 3. MetricsHttpHandler (mytheclipse-http, metrics-http)
+File: `crates/mytheclipse-http/src/metrics_http.rs`
+- new feature `metrics-http` (axum + tower + mytheclipse/observability)
+- `metrics_routes(collector) -> Router` serving `/metrics` (Prometheus text via `export_prometheus`) + `/`
+- `tower` dep added (util feature)
+- 1 test via ServiceExt::oneshot
+
+## Verification
+- `cargo build --workspace --all-features` → exit 0
+- `cargo test --workspace --all-features` → all pass (160+ tests)
+- `cargo clippy --workspace --all-features` → no new warnings