docs(governance): MCP restart governance and authorization policy (#656)

Adds docs/architecture/mcp-restart-governance.md, the restart-governance/v1 ADR
defining who may restart the MCP control plane and under what conditions.

- Recovery ladder (reconnect -> rebind -> scoped restart -> full restart -> host)
  with restart stated as the last resort.
- Authorization matrix across author/reviewer/merger/reconciler/controller/
  operator/admin; no LLM worker role may perform or authorize a full or host
  restart.
- v1 authority decision recorded: controller approval + automated safety gates;
  quorum deferred to a superseding ADR.
- Break-glass path with pre-declared incident and mandatory post-hoc audit.
- Ambiguous policy state denies restart.
- Stable policy IDs RG-01..RG-08 for later enforcement code to bind to.

Cross-links the ADR from docs/safety-model.md and docs/webui-deployment.md, and
adds tests/test_mcp_restart_governance_docs.py asserting acceptance criteria 1-5.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

docs/safety-model.md

@@ -46,3 +46,17 @@ If shell helpers are unavailable and MCP commit cannot run, stop with a recovery
 report (restart session, clear hung terminals, use MCP-native commit). See
 [`llm-workflow-runbooks.md`](llm-workflow-runbooks.md) § MCP-native commit path
 (#260) and agent temp artifact cleanup (#261).
+
+## 7. Process restart governance
+
+Restarting the MCP control-plane process is destructive to concurrent multi-role
+work and is governed by a dedicated policy. Restart is a **last resort** behind
+narrower recoveries (reconnect, rebind), full/host restart is reserved to
+operator/admin under **controller approval + automated safety gates**, a
+unilateral LLM or operator full restart with active peers is **forbidden**, and
+ambiguous policy state **denies** restart. Break-glass is a separate,
+incident-backed path with a mandatory audit.
+
+See [`architecture/mcp-restart-governance.md`](architecture/mcp-restart-governance.md)
+(#656) for the authorization matrix, the recovery ladder, break-glass
+conditions, and the `RG-01`–`RG-08` policy IDs.