Keep active transfers connected when the app returns to foreground (#8651)

* fix(client): keep active transfers alive during foreground checks

Foreground used an independent three-second probe that closed live connections while a pong waited behind bulk data. Share the heartbeat clock and refresh its outstanding deadline on validated inbound frames, including incomplete chunk assemblies.

* test(client): deliver bulk response before the queued pong

* fix(client): preserve latency deadlines when sharing heartbeat pings

* fix(client): keep heartbeat cadence during active downloads

packages/protocol/src/chunked-transport.ts

@@ -25,6 +25,7 @@ export class ChunkedTransport {
       supportsDrain?: boolean;
       send: (frame: Frame, waitForDrain: boolean) => void | Promise<void>;
       deliver: (frame: Frame) => void;
+      onActivity?: () => void;
       onFailure?: (error: unknown) => void;
     },
   ) {
@@ -134,6 +135,7 @@ export class ChunkedTransport {
         { cause: error },
       );
     }
+    this.io.onActivity?.();
     if (message !== undefined) this.io.deliver(message);
   }