Fix long dictation retry backpressure

Treat Node IPC backpressure as a queue signal instead of a failed send, and pace buffered dictation replay so finish waits for the backlog to flush.

packages/app/src/dictation/dictation-stream-sender.test.ts

@@ -137,4 +137,30 @@ describe("DictationStreamSender", () => {
 
     expect(client.chunks.map((c) => c.seq)).toEqual([0, 1]);
   });
+
+  it("does not replay long buffered native dictation in one synchronous burst", async () => {
+    const client = new FakeDaemonClient();
+    client.isConnected = false;
+    const sender = new DictationStreamSender({
+      client: client as unknown as DaemonClient,
+      format: "audio/pcm;rate=16000;bits=16",
+      createDictationId: () => "d1",
+    });
+
+    for (let seq = 0; seq < 480; seq += 1) {
+      sender.enqueueSegment(`native-frame-${seq}`);
+    }
+
+    client.isConnected = true;
+    const finish = sender.finish(sender.getFinalSeq());
+
+    await tick();
+
+    expect(client.chunks.length).toBeLessThanOrEqual(128);
+    await expect(finish).resolves.toEqual({
+      dictationId: "d1",
+      text: "ok",
+    });
+    expect(client.finishes).toEqual([{ dictationId: "d1", finalSeq: 479 }]);
+  });
 });