Ref #1. 04. Starting an Updated System or Service

adr/ADR-005-package-based-updates.md

@@ -90,7 +90,7 @@ The package manager is responsible for:
 - verifying signatures and integrity;
 - executing installation scripts;
 - replacing files;
-- retaining previously installed versions.
+- retaining previous packages when configured to do so, or working with a separate local package store.
 
 The OTA manager is responsible for update policy, including when updates are allowed, network restrictions, user approval, and operational conditions.
 
@@ -98,9 +98,11 @@ Using a package manager alone does not constitute a complete OTA solution.
 
 ### Component Rollback
 
-Each component can be upgraded and downgraded independently.
+An independent component can be restored without reverting the entire system when the package manager supports downgrade and the previous version remains compatible with its dependencies, configuration, and data.
 
-Most package managers retain previously installed versions, allowing an individual component to be rolled back without reverting the entire system.
+The update design must keep the previous package available. Automatic retention must be checked for the selected package manager; it cannot be assumed.
+
+[ADR-015: Service Checks and Package Downgrade](ADR-015-service-checks-and-package-downgrade.md) describes a recovery policy for a service that fails after an update. It covers startup checks, an explicit downgrade, a saved block against retrying the failed version, and reporting. That example requires local retention of the previous package and verified downgrade support.
 
 ## Limitations