feat(verifier): report a relaunch on state.lastAction

pkg/spec/src/types.ts

@@ -109,8 +109,17 @@ export interface ExceptionRecord {
  * tap landed. Null is unknown, not "it did not happen" (`state.lastAction` is
  * itself null for that), so a property attributing an effect to this action
  * has to decline unless `applied` is true.
+ *
+ * `relaunched` is true when the runner had to bring the app back to the
+ * foreground after this action, so the previous reading and the current one
+ * straddle a restart. The action itself still happened; what a property cannot
+ * assume across it is that app state ran continuously between the two readings,
+ * and one demanding an effect of this action has to decline. Null is "not
+ * reported", which is weaker than "the app never restarted": a target whose
+ * foreground the runner cannot read never relaunches the app and cannot promise
+ * that either.
  */
-export type LastAction = Action & { applied: true | null };
+export type LastAction = Action & { applied: true | null; relaunched: true | null };
 
 export interface State {
   snapshots: Snapshots;