R-1342: a restore copy under the stable-start watch is not deletable (D62 gap); an app removed during the watch raises no alarm — tests red first; commit only

controller/cmd/controller/main.go

@@ -3197,6 +3197,17 @@ func (a *stackAdapter) StopStack(name string) error {
 	return a.mgr.StopStack(name)
 }
 
+// StackRemoved answers backup's optional StackRemovalReporter (R-1342): the app is known and no longer installed — a
+// stable-start watch then ends quietly instead of alarming „did not start". An app this box does not know at all is
+// not „removed" (no answer → the watch goes on as before).
+func (a *stackAdapter) StackRemoved(name string) bool {
+	s, ok := a.mgr.GetStack(name)
+	return ok && !s.Deployed
+}
+
+// The watch reaches StackRemoved through a type assertion; this line makes the adapter's answer a compile-time fact.
+var _ backup.StackRemovalReporter = (*stackAdapter)(nil)
+
 // IsDeploying answers backup's optional deployingReporter (R-634): the volume leg asks it again
 // immediately before it stops an app, because its list is taken once at the start of the run.
 func (a *stackAdapter) IsDeploying(name string) bool {