fix(copilot): mark native image requests as vision

Co-authored-by: dhabibi <9087935+dhabibi@users.noreply.github.com>

tests/run_agent/test_copilot_native_vision_headers.py

@@ -0,0 +1,96 @@
+from unittest.mock import MagicMock, patch
+
+from run_agent import AIAgent
+
+
+def _make_copilot_agent():
+    with patch("run_agent.OpenAI") as mock_openai:
+        mock_openai.return_value = MagicMock()
+        agent = AIAgent(
+            api_key="gh-token",
+            base_url="https://api.githubcopilot.com",
+            provider="copilot",
+            model="gpt-5.4",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+    return agent
+
+
+def test_request_client_adds_copilot_vision_header_for_native_image_payload():
+    agent = _make_copilot_agent()
+    built_kwargs = []
+
+    def fake_create(kwargs, *, reason, shared):
+        built_kwargs.append(dict(kwargs))
+        return MagicMock()
+
+    api_kwargs = {
+        "model": "gpt-5.4",
+        "messages": [
+            {
+                "role": "user",
+                "content": [
+                    {"type": "text", "text": "What is in this image?"},
+                    {"type": "image_url", "image_url": {"url": "data:image/png;base64,abc"}},
+                ],
+            }
+        ],
+    }
+
+    agent.client = object()
+    with patch.object(agent, "_is_openai_client_closed", return_value=False), patch.object(
+        agent, "_create_openai_client", side_effect=fake_create
+    ):
+        agent._create_request_openai_client(reason="test", api_kwargs=api_kwargs)
+
+    headers = built_kwargs[-1]["default_headers"]
+    assert headers["Copilot-Vision-Request"] == "true"
+
+
+def test_request_client_leaves_copilot_text_requests_without_vision_header():
+    agent = _make_copilot_agent()
+    built_kwargs = []
+
+    def fake_create(kwargs, *, reason, shared):
+        built_kwargs.append(dict(kwargs))
+        return MagicMock()
+
+    api_kwargs = {"model": "gpt-5.4", "messages": [{"role": "user", "content": "hello"}]}
+
+    agent.client = object()
+    with patch.object(agent, "_is_openai_client_closed", return_value=False), patch.object(
+        agent, "_create_openai_client", side_effect=fake_create
+    ):
+        agent._create_request_openai_client(reason="test", api_kwargs=api_kwargs)
+
+    headers = built_kwargs[-1]["default_headers"]
+    assert "Copilot-Vision-Request" not in headers
+
+
+def test_request_client_does_not_add_vision_header_after_non_vision_fallback():
+    agent = _make_copilot_agent()
+    built_kwargs = []
+
+    def fake_create(kwargs, *, reason, shared):
+        built_kwargs.append(dict(kwargs))
+        return MagicMock()
+
+    # This is the shape after _prepare_messages_for_non_vision_model has
+    # replaced image parts with text, so Copilot should not get the vision route.
+    api_kwargs = {
+        "model": "gpt-5.4",
+        "messages": [
+            {"role": "user", "content": "[user image: a dog]\n\nWhat is in this image?"}
+        ],
+    }
+
+    agent.client = object()
+    with patch.object(agent, "_is_openai_client_closed", return_value=False), patch.object(
+        agent, "_create_openai_client", side_effect=fake_create
+    ):
+        agent._create_request_openai_client(reason="test", api_kwargs=api_kwargs)
+
+    headers = built_kwargs[-1]["default_headers"]
+    assert "Copilot-Vision-Request" not in headers