refactor: remove legacy assistant compatibility

backend/tests/test_voice_webrtc_lifecycle.py

@@ -52,7 +52,7 @@ class WebRTCOfferMetadataTest(unittest.IsolatedAsyncioTestCase):
             ["set_photo_button_visible", "show_message"],
         )
 
-    async def test_client_tool_request_data_remains_a_compatibility_fallback(self):
+    async def test_client_tool_request_data_is_not_a_capability_channel(self):
         request = offer_request()
         payload = {
             "sdp": "offer",
@@ -68,7 +68,7 @@ class WebRTCOfferMetadataTest(unittest.IsolatedAsyncioTestCase):
             await voice_webrtc.http_offer(request, payload)
 
         forwarded = handle_offer.await_args.args[0]
-        self.assertEqual(forwarded["client_tool_names"], ["show_message"])
+        self.assertEqual(forwarded["client_tool_names"], [])
 
     async def test_invalid_client_tool_header_is_rejected(self):
         request = offer_request(client_tools={"name": "show_message"})