feat(tunnel): 请求体流式传输 & OpenAI CLI 请求 key 排序优化

Hub 端:
- open_local_stream 不再接收 body 参数，改为通过 push_local_request_body 分块推送
- 请求体按 32KB 分帧发送，避免大请求一次性压缩和传输
- local_relay 改为流式解析 envelope 和转发请求体

Proxy 端:
- stream_handler 改为流式传输请求体到上游，不再预先收集完整 body
- upstream_client 请求体类型从 Full<Bytes> 改为 UnsyncBoxBody 以支持流式传输
- dispatcher 将 StreamEnd/StreamError 事件转发给 stream handler

Python 端:
- hub_transport relay envelope 改为异步生成器流式发送
- 提取 reorder_openai_cli_request_prefix_keys 为公共函数
- Codex passthrough 路径也应用稳定的前缀 key 排序

tests/unit/test_hub_transport_heartbeat.py

@@ -15,6 +15,7 @@ class _FakeRelayClient:
     def __init__(self, response: httpx.Response) -> None:
         self.response = response
         self.sent_request: httpx.Request | None = None
+        self.sent_body: bytes | None = None
 
     def build_request(self, method: str, url: str, **kwargs: Any) -> httpx.Request:
         return httpx.Request(method, url, **kwargs)
@@ -22,6 +23,7 @@ class _FakeRelayClient:
     async def send(self, request: httpx.Request, *, stream: bool = False) -> httpx.Response:
         _ = stream
         self.sent_request = request
+        self.sent_body = await request.aread()
         self.response.request = request
         return self.response
 
@@ -56,7 +58,7 @@ async def test_transport_encodes_local_relay_envelope(monkeypatch: pytest.Monkey
     await response.aclose()
 
     assert fake_client.sent_request is not None
-    payload = fake_client.sent_request.content
+    payload = fake_client.sent_body
     assert payload is not None
     meta_len = struct.unpack("!I", payload[:4])[0]
     meta = json.loads(payload[4 : 4 + meta_len].decode("utf-8"))
@@ -88,3 +90,33 @@ async def test_transport_maps_relay_timeout_to_read_timeout(
 
     with pytest.raises(httpx.ReadTimeout, match="relay timed out"):
         await transport.handle_async_request(request)
+
+
+@pytest.mark.asyncio
+async def test_transport_streams_request_body_from_async_generator(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    transport = HubTunnelTransport("node-1", timeout=12.0)
+    fake_client = _FakeRelayClient(httpx.Response(200, content=b"ok"))
+    monkeypatch.setattr("src.services.proxy_node.hub_transport.get_hub_config", _relay_config)
+    monkeypatch.setattr(transport, "_relay_client", fake_client)
+
+    async def body() -> Any:
+        yield b'{"hello":'
+        yield b'"world"}'
+
+    request = httpx.Request(
+        "POST",
+        "https://example.com/v1/chat/completions",
+        headers={"content-type": "application/json"},
+        content=body(),
+    )
+
+    response = await transport.handle_async_request(request)
+    assert response.status_code == 200
+    await response.aclose()
+
+    payload = fake_client.sent_body
+    assert payload is not None
+    meta_len = struct.unpack("!I", payload[:4])[0]
+    assert payload[4 + meta_len :] == b'{"hello":"world"}'