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WZP-P2-T5-S2: Per-session Prometheus metrics - 5 new per-session gauges/counters: buffer_depth, loss_pct, rtt_ms, underruns, overruns — all labeled by session_id - update_session_quality() reads QualityReport from packet headers - update_session_buffer() tracks jitter buffer state per session - remove_session_metrics() cleans up labels on disconnect - Delta-aware counter increments avoid double-counting - 2 tests: session_quality_update, session_metrics_cleanup WZP-P2-T5-S5: Inter-relay health probe - New probe.rs: ProbeConfig, ProbeMetrics, SlidingWindow, ProbeRunner - --probe <addr> flag (repeatable) spawns background probe per target - Sends Ping/s over QUIC, receives Pong, computes RTT/loss/jitter - SlidingWindow(60): tracks last 60 pings, loss = missed pongs, jitter = std deviation of RTT - Prometheus gauges: wzp_probe_rtt_ms, loss_pct, jitter_ms, up with target label - Probe connections use SNI "_probe" — relay responds with Pong loop, skipping auth/handshake - Auto-reconnect with 5s backoff on disconnect - 6 tests: metrics_register, rtt/loss/jitter calculation, window eviction, empty edge cases 231 tests passing across all crates. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>