Fix review perf issues.

web/src/App.tsx

@@ -373,21 +373,20 @@ export default function App() {
   }, []);
 
   // Live updates. Every event on this stream is about this review — the stream is
-  // the tab's own — so anything that isn't the opening handshake means the comment
-  // list moved and is worth refetching.
+  // the tab's own — so anything that arrives means the comment list moved and is
+  // worth refetching.
+  //
+  // The handshake refetches too, which it did not used to. The stream is dropped
+  // while the pane is hidden (see useSSE) and reconnects when it comes back, so
+  // `connected` is the one moment the rail is known to be behind: every comment
+  // written while this pane was off screen is a frame nobody was listening for.
+  // Treating the handshake as "something changed" is what closes that gap — and
+  // the same gap after a dropped connection, which was always there.
   //
   // Comments only. The diff is not pushed: the server has no watcher on the work
   // tree, and a comment arriving is a change to the rail, which can be applied
   // under the reader safely. A changed *diff* cannot — see the poll below.
-  useSSE(
-    useCallback(
-      (e) => {
-        if (e.type === 'connected') return;
-        refetchComments();
-      },
-      [refetchComments],
-    ),
-  );
+  useSSE(useCallback(() => refetchComments(), [refetchComments]));
 
   // Notice that the diff on screen has been overtaken, and say so. Nothing here
   // reloads anything: it sets `stale`, the banner offers the refresh, and the