Many imorovments

ui/dr-ui/src/library_ui.rs

@@ -1650,14 +1650,22 @@ fn drain_thumbnails(
                     // carry no embedded preview.
                     ThumbnailMessage::Ready(t) => {
                         w.set_library_thumbs_done(w.get_library_thumbs_done() + 1);
-                        // Bytes arrived, so the server is reachable. This is
-                        // what clears the banner when a connection returns
-                        // while the user is simply scrolling, without waiting
-                        // for a probe or a manual retry.
-                        if ctl_cb
-                            .reachability
-                            .borrow_mut()
-                            .mark_reachable(std::time::Instant::now())
+                        // Bytes arrived *from the server*, so it is reachable.
+                        // This is what clears the banner when a connection
+                        // returns while the user is simply scrolling, without
+                        // waiting for a probe or a manual retry.
+                        //
+                        // Store hits are excluded deliberately: they are read
+                        // from local disk and say nothing about the network. A
+                        // window that is mostly cached delivers a run of them
+                        // before the first request is even attempted, so
+                        // counting them declared "back online" against a server
+                        // that was plainly down.
+                        if !t.from_cache
+                            && ctl_cb
+                                .reachability
+                                .borrow_mut()
+                                .mark_reachable(std::time::Instant::now())
                         {
                             log::info!("back online");
                             refresh_offline(&w, &ctl_cb);