docs(core): define compatibility retention policy

docs/RELEASE_DEPENDENCIES.md

@@ -803,6 +803,12 @@ collecting release evidence.
 
 ## Migration Baselines
 
+Release migration support follows `COMPATIBILITY_POLICY.md`: every tagged
+`0.1.x` installation is a supported upgrade origin, released revision IDs are
+immutable, and migration-only reconciliation remains available for at least one
+subsequent major release cycle after the matching runtime compatibility path is
+removed.
+
 Development migrations may be small and numerous while a feature is moving.
 GovOPlaN keeps those detailed migrations on an explicit development track and
 publishes reviewed release shortcuts on the release track. Before a stable