fix(metadata): qwen3.6-plus has a 1M context window (#27008)

agent/model_metadata.py

@@ -194,6 +194,7 @@ def _strip_provider_prefix(model: str) -> str:
     "llama": 131072,
     # Qwen — specific model families before the catch-all.
     # Official docs: https://help.aliyun.com/zh/model-studio/developer-reference/
+    "qwen3.6-plus": 1048576,      # 1M context (DashScope/Alibaba & OpenRouter)
     "qwen3-coder-plus": 1000000,  # 1M context
     "qwen3-coder": 262144,        # 256K context
     "qwen": 131072,

tests/agent/test_model_metadata.py

@@ -746,6 +746,16 @@ def test_qwen3_coder_context_length(self, mock_fetch):
         mock_fetch.return_value = {}
         assert get_model_context_length("qwen3-coder") == 262144
 
+    @patch("agent.model_metadata.fetch_model_metadata")
+    def test_qwen3_6_plus_context_length(self, mock_fetch):
+        """qwen3.6-plus has a 1M context window, not the generic 128K Qwen default."""
+        mock_fetch.return_value = {}
+        assert get_model_context_length("qwen3.6-plus") == 1048576
+        # Provider-prefixed variants must resolve to the same explicit entry
+        # via the longest-substring fallback (no portal/OR cache available).
+        assert get_model_context_length("qwen/qwen3.6-plus") == 1048576
+        assert get_model_context_length("dashscope/qwen3.6-plus") == 1048576
+
     @patch("agent.model_metadata.fetch_model_metadata")
     def test_qwen_generic_context_length(self, mock_fetch):
         """Generic qwen models still get the 128K default."""