test(deepseek): cover async tool filtering and document tool_choice assumption

Add an async_transform_request regression test so the sync and async tool
filtering paths cannot silently diverge, and document in _drop_unsupported_tools
that only non-function tools are dropped, so a function-named tool_choice always
references a surviving tool

litellm/llms/deepseek/chat/transformation.py

@@ -157,6 +157,11 @@ class DeepSeekChatConfig(OpenAIGPTConfig):
         #30722). Drop the unsupported entries so the function tools still go
         through, and drop the now-dangling tool_choice/parallel_tool_calls when
         nothing callable survives.
+
+        Only non-`function` tools are ever dropped, so a `tool_choice` that names
+        a specific function still points at a surviving tool and is left intact;
+        `tool_choice`/`parallel_tool_calls` are cleared only when no function
+        tool remains.
         """
         tools = optional_params.get("tools")
         if not isinstance(tools, list) or not tools:

tests/test_litellm/llms/deepseek/chat/test_deepseek_chat_transformation.py

@@ -81,3 +81,23 @@ def test_transform_request_strips_unsupported_tools_from_body():
 
     assert [tool["type"] for tool in body["tools"]] == ["function"]
     assert body["tools"][0]["function"]["name"] == "shell"
+
+
+async def test_async_transform_request_strips_unsupported_tools_from_body():
+    config = DeepSeekChatConfig()
+    body = await config.async_transform_request(
+        model="deepseek-chat",
+        messages=[{"role": "user", "content": "hi"}],
+        optional_params={
+            "tools": [
+                _function_tool("shell"),
+                {"type": "namespace", "name": "container.exec"},
+            ],
+            "tool_choice": "auto",
+        },
+        litellm_params={},
+        headers={},
+    )
+
+    assert [tool["type"] for tool in body["tools"]] == ["function"]
+    assert body["tools"][0]["function"]["name"] == "shell"