test(vision-manager): extract refresh_running_after_mem_check; assert log distinguishes fix from bug (0.87.18)

Two 0.87.15 ship-blockers:

1. mem_check_and_stop test now ALSO greps for the "deferring to next
   tick" warning — distinguishes fix from bug. Mutation-confirmed.

2. Extract `refresh_running_after_mem_check` (sets global instead of
   echoing so loop-scope flags persist across calls) and drive it
   directly from the harness, closing the structurally-untestable
   post-mem refresh ERR guard.

Adjacent: log-on-flip gating on both ERR warnings; `log` to stderr;
dangling-TempDir in app::tests reclaim test fixed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/app.rs

@@ -1425,9 +1425,15 @@ mod tests {
         .await
         .unwrap();
 
-        let storage: Arc<dyn Storage> = Arc::new(LocalStorage::new(
-            tempfile::tempdir().unwrap().path(),
-        ));
+        // Bind to a local so the TempDir lives for the rest of the test.
+        // `tempfile::tempdir().unwrap().path()` would drop the TempDir
+        // at end-of-expression and `LocalStorage` would hold a path to
+        // a deleted directory. (Today this is fine because the dispatch
+        // fails before storage is touched, but it makes the test fragile
+        // to any future code rearrangement.)
+        let storage_dir = tempfile::tempdir().unwrap();
+        let storage: Arc<dyn Storage> =
+            Arc::new(LocalStorage::new(storage_dir.path()));
         let mut cfg = crate::config::AnalysisConfig::default();
         cfg.workers = 1;
         cfg.job_timeout = Duration::from_secs(1);