Integrate verified installation flow (T-302)

core/installer/switcher.go

@@ -36,8 +36,8 @@ func (err *RollbackError) Error() string {
 	return fmt.Sprintf("%s: health=%v; rollback=%v", ErrRollbackFailed, err.Health, err.Rollback)
 }
 
-func (err *RollbackError) Unwrap() error {
-	return ErrRollbackFailed
+func (err *RollbackError) Unwrap() []error {
+	return []error{ErrRollbackFailed, err.Health, err.Rollback}
 }
 
 // Switcher activates a verified staging directory and runs an injected check.
@@ -141,7 +141,7 @@ func (switcher *Switcher) Switch(root string) error {
 		if err := removeTransactionWithFence(layout, fence); err != nil {
 			return &RollbackError{Health: healthErr, Rollback: err}
 		}
-		return fmt.Errorf("%w: %v", ErrHealthCheckFailed, healthErr)
+		return fmt.Errorf("%w: %w", ErrHealthCheckFailed, healthErr)
 	}
 
 	record.Phase = phaseCommitted