docs: adopt release-candidate closeout cadence

AGENTS.md

@@ -15,6 +15,14 @@
   conflicts fail-closed.
 - Prefer one synchronized bootstrap, one atomic proposal registration, one reviewed diff, and one
   exact hash-bound application over caller-managed operation chaining.
+- Read canonical documentation during intake, but keep it read-only while implementation and
+  focused testing are still changing the candidate.
+- Freeze and validate one release candidate before registering documentation changes. After the
+  candidate is green, perform one atomic documentation closeout, run documentation-only
+  validation, and then publish the final revision.
+- Allow at most one narrow evidence-only documentation correction after deployment. If validation
+  finds an implementation defect, abandon or rebase the proposal and return to implementation
+  instead of documenting a failed candidate.
 - Keep dependencies small and pinned by compatible major version.
 - Run strict `pyright`, `npm run lint:web`, formatting, Ruff, compilation, focused tests, and the
   complete warning-strict test suite before closing a gate.