test(installer): pin own-pid adopt for desktop-prewritten update marker

Regression for #74761: acquire must succeed when the marker already
names this process (desktop writeUpdateMarker raced ahead), and still
clean up on Drop.

apps/bootstrap-installer/src-tauri/src/update.rs

@@ -1381,6 +1381,43 @@ mod tests {
         let _ = std::fs::remove_dir_all(&dir);
     }
 
+    #[test]
+    fn acquire_adopts_a_marker_prewritten_with_our_own_pid() {
+        // #74761: desktop writeUpdateMarker(hermesHome, child.pid) races ahead
+        // of UpdateMarkerGuard::acquire. The marker names US; refusing it made
+        // every in-app desktop update loop forever. Adopt and rewrite.
+        let dir = unique_tmp_dir("marker-own-pid");
+        std::fs::create_dir_all(&dir).unwrap();
+        let marker = dir.join(".hermes-update-in-progress");
+
+        let started_at = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .map(|d| d.as_secs())
+            .unwrap_or(0)
+            .saturating_sub(2);
+        std::fs::write(&marker, format!("{}\n{started_at}", std::process::id())).unwrap();
+
+        let guard = UpdateMarkerGuard::acquire(marker.clone()).unwrap_or_else(|owner| {
+            panic!(
+                "own-pid pre-write must be adoptable, got foreign owner pid={}",
+                owner.pid
+            )
+        });
+        assert!(marker.exists(), "adopted guard must own the marker");
+        let body = std::fs::read_to_string(&marker).unwrap();
+        assert_eq!(
+            body.lines().next().unwrap().trim().parse::<u32>().unwrap(),
+            std::process::id(),
+            "acquire rewrites the marker with our pid + fresh started_at"
+        );
+        drop(guard);
+        assert!(
+            !marker.exists(),
+            "Drop must still clear the marker we adopted"
+        );
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn acquire_reclaims_a_marker_owned_by_a_dead_pid() {
         let dir = unique_tmp_dir("marker-dead-pid");