fix(01-review): sweep #5 surface port-replaced-during-fetch diagnostic on buffer timeout

src/background/index.ts

@@ -133,7 +133,20 @@ async function getVideoBufferFromOffscreen(): Promise<VideoBufferResponse> {
   return new Promise<VideoBufferResponse>((resolve) => {
     const timer = setTimeout(() => {
       port.onMessage.removeListener(handler);
-      logger.warn(`Buffer fetch timed out after ${BUFFER_FETCH_TIMEOUT_MS} ms`);
+      // Sweep #5 fix: surface the diagnostic when the timeout fires
+      // because the port was replaced by a reconnect mid-request.
+      // The OLD port (captured as `port`) has a dead listener; the
+      // offscreen will encode-and-send on the NEW port but the
+      // listener installed there belongs to a different
+      // getVideoBufferFromOffscreen call (if any). Without this
+      // diagnostic the operator sees a silent timeout that masquerades
+      // as an offscreen-side problem. With it, the SW log shows the
+      // reconnect timing was the proximate cause.
+      const portReplaced = videoPort !== port;
+      logger.warn(
+        `Buffer fetch timed out after ${BUFFER_FETCH_TIMEOUT_MS} ms`,
+        'port_replaced_during_fetch:', portReplaced,
+      );
       resolve({ segments: [] });
     }, BUFFER_FETCH_TIMEOUT_MS);
     const handler = (msg: unknown) => {