docs(framework): P3.1 fast-follow — governance wording + gate scope + bare-launch note

Non-blocking items from the #575 dual-engine review:
- CONSTITUTION.md: state explicitly there is NO CONSTITUTION.local.md and hard
  gates are not locally overridable (clarity vs LAYER-MODEL overlay-eligibility)
- verify-sanitized.sh: expand identity scan to *.yml/*.yaml/*.toml/*.env/*.service
  (operator data could hide in shipped configs) — gate green, no new hits
- AGENTS.md: clarify the intentional bare-launch stop-if-missing strictness vs the
  launcher's readOptional tolerance (which keeps pre-upgrade hosts working)

Refs #542, closes #576

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/mosaic/framework/defaults/AGENTS.md

@@ -70,6 +70,9 @@ Skills, hooks, MCP, and plugins are force multipliers you MUST use when applicab
 ## Missing core file
 
 If `CONSTITUTION.md`, `AGENTS.md`, `SOUL.md`, or the runtime contract is missing, stop and report it.
+This agent-facing strictness is intentional and stricter than the launcher: the launcher injects
+`CONSTITUTION.md` tolerantly (skipping it if absent so pre-upgrade hosts keep working), but once a host
+is re-seeded a genuinely missing core file is a stop-and-report condition — not something to proceed past.
 
 ## Session Closure