fix: refresh copilot token before requests

Address PR review feedback by avoiding an async method reference as the OpenAI client api_key.

Initialize the client with a placeholder key, refresh the Copilot token before each chat/chat_stream call, and update the runtime client api_key before dispatch.

Add a regression test that verifies the client api_key is refreshed to a real string before chat requests.

Generated with GitHub Copilot, GPT-5.4.

tests/cli/test_commands.py

@@ -357,6 +357,35 @@ def test_github_copilot_provider_strips_prefixed_model_name():
     assert kwargs["model"] == "gpt-5.1"
 
 
+@pytest.mark.asyncio
+async def test_github_copilot_provider_refreshes_client_api_key_before_chat():
+    from nanobot.providers.github_copilot_provider import GitHubCopilotProvider
+
+    mock_client = MagicMock()
+    mock_client.api_key = "no-key"
+    mock_client.chat.completions.create = AsyncMock(return_value={
+        "choices": [{"message": {"content": "ok"}, "finish_reason": "stop"}],
+        "usage": {"prompt_tokens": 1, "completion_tokens": 1, "total_tokens": 2},
+    })
+
+    with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI", return_value=mock_client):
+        provider = GitHubCopilotProvider(default_model="github-copilot/gpt-5.1")
+
+    provider._get_copilot_access_token = AsyncMock(return_value="copilot-access-token")
+
+    response = await provider.chat(
+        messages=[{"role": "user", "content": "hi"}],
+        model="github-copilot/gpt-5.1",
+        max_tokens=16,
+        temperature=0.1,
+    )
+
+    assert response.content == "ok"
+    assert provider._client.api_key == "copilot-access-token"
+    provider._get_copilot_access_token.assert_awaited_once()
+    mock_client.chat.completions.create.assert_awaited_once()
+
+
 def test_openai_codex_strip_prefix_supports_hyphen_and_underscore():
     assert _strip_model_prefix("openai-codex/gpt-5.1-codex") == "gpt-5.1-codex"
     assert _strip_model_prefix("openai_codex/gpt-5.1-codex") == "gpt-5.1-codex"