fix tests: restore chat_response + invoke_result + chat_request imports

CI failure was 'name chat_response is not defined' in server.ws_connect
proxy path, plus invoke_result used in invoke flow. client.chat() needs
chat_request at module level too — inline import was a smell. tests pass
locally now (pytest 10/10 in venv).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Zawwarsami16

zhub/client.py

@@ -23,7 +23,7 @@
 
 from .manifest import Capability, Manifest, chat_only_manifest
 from .protocol import (
-    Envelope, register_publisher, register_connection,
+    Envelope, register_publisher, register_connection, chat_request,
     invoke_request, invoke_result,
 )
 from .errors import AuthError, ConnectionError as ZhubConnectionError
@@ -225,7 +225,6 @@ async def chat(self, messages: list[dict[str, Any]],
                    model: str = "default", temperature: float = 0.4,
                    max_tokens: int = 4096, timeout: float = 60.0) -> dict[str, Any]:
         """Send a chat request through the hub to the AI."""
-        from .protocol import chat_request
         env = chat_request(messages, model, temperature, max_tokens)
         future = asyncio.get_running_loop().create_future()
         self._pending[env.request_id] = future

zhub/server.py

@@ -38,8 +38,8 @@
     ) from e
 
 from .protocol import (
-    Envelope, registered, chat_request,
-    invoke_request, connection_event, error_envelope, new_request_id,
+    Envelope, registered, chat_request, chat_response,
+    invoke_request, invoke_result, connection_event, error_envelope, new_request_id,
 )