APR-Lite Phase 36: Stabilization, Observability & Governance Health Certificate

This document is the canonical technical record for APR‑Lite Phase 36, which provides the stabilization and observability layer that completes the substrate governance platform. Phase 36 introduces four capabilities: (36.1) a runtime chain‑health status surfaced in every Guard receipt, derived from a recent integrity assessment of the active chain; (36.2) human‑readable mediation error messages with actionable hints in place of opaque error codes; (36.3) enhanced metrics that expose session‑level correlation behavior for operators; and (36.4) a Governance Health Certificate — a signed, time‑stamped interface that reports the current integrity posture of the substrate. The validation suite remains fully passing across the phase boundary. Phase 36 introduces no new invariants, no new chain fields, and no new cryptographic primitives, and makes the substrate self‑aware, self‑reporting, and operator‑friendly.