[v0.25.1rc][BugFix][Frontend] Align DeepSeek V4 system tool rendering

tests/ut/patch/platform/test_deepseek_v4_thinking.py

@@ -98,6 +98,69 @@ def fake_encode_messages(messages, **kwargs):
     assert captured_kwargs[-1]["reasoning_effort"] == expected_effort
 
 
+@pytest.mark.parametrize(
+    ("reasoning_effort", "expected_effort"),
+    [
+        (None, "high"),
+        ("high", "high"),
+        ("low", "low"),
+    ],
+)
+def test_deepseek_v4_tokenizer_attaches_tools_to_existing_system(
+    monkeypatch,
+    reasoning_effort,
+    expected_effort,
+):
+    captured_messages = []
+    captured_kwargs = []
+
+    def fake_encode_messages(messages, **kwargs):
+        captured_messages.append(messages)
+        captured_kwargs.append(kwargs)
+        return "prompt"
+
+    monkeypatch.setattr(deepseek_v4, "encode_messages", fake_encode_messages)
+    tokenizer = deepseek_v4.get_deepseek_v4_tokenizer(FakeTokenizer())
+    messages = [
+        {"role": "system", "content": "system prompt"},
+        {"role": "user", "content": "hi"},
+    ]
+    tools = [{"type": "function", "function": {"name": "get_weather"}}]
+    original_messages = [message.copy() for message in messages]
+    kwargs = {"reasoning_effort": reasoning_effort} if reasoning_effort is not None else {}
+
+    tokenizer.apply_chat_template(messages, tools=tools, tokenize=False, **kwargs)
+
+    assert captured_messages[-1] == [
+        {"role": "system", "content": "system prompt", "tools": tools},
+        {"role": "user", "content": "hi"},
+    ]
+    assert captured_kwargs[-1]["reasoning_effort"] == expected_effort
+    assert messages == original_messages
+
+
+def test_deepseek_v4_tokenizer_adds_system_for_tools_when_missing(monkeypatch):
+    captured_messages = []
+
+    def fake_encode_messages(messages, **kwargs):
+        captured_messages.append(messages)
+        return "prompt"
+
+    monkeypatch.setattr(deepseek_v4, "encode_messages", fake_encode_messages)
+    tokenizer = deepseek_v4.get_deepseek_v4_tokenizer(FakeTokenizer())
+    messages = [{"role": "user", "content": "hi"}]
+    tools = [{"type": "function", "function": {"name": "get_weather"}}]
+    original_messages = [message.copy() for message in messages]
+
+    tokenizer.apply_chat_template(messages, tools=tools, tokenize=False)
+
+    assert captured_messages[-1] == [
+        {"role": "system", "tools": tools},
+        {"role": "user", "content": "hi"},
+    ]
+    assert messages == original_messages
+
+
 def test_deepseek_v4_defaults_to_thinking_with_high_effort():
     tokenizer = deepseek_v4.get_deepseek_v4_tokenizer(FakeTokenizer())
     prompt = tokenizer.apply_chat_template(

vllm_ascend/patch/platform/patch_deepseek_v4_thinking.py

@@ -94,8 +94,16 @@ def apply_chat_template(
         conversation = kwargs.get("conversation", messages)
         messages = conversation.copy()
         if tools is not None and len(tools) > 0:
-            messages.insert(0, {"role": "system"})
-            messages[0]["tools"] = tools  # type: ignore[typeddict-unknown-key]
+            system_index = next(
+                (index for index, message in enumerate(messages) if message.get("role") == "system"),
+                None,
+            )
+            if system_index is None:
+                messages.insert(0, {"role": "system", "tools": tools})
+            else:
+                system_message = messages[system_index].copy()
+                system_message["tools"] = tools  # type: ignore[typeddict-unknown-key]
+                messages[system_index] = system_message
 
         reasoning_effort = kwargs.get("reasoning_effort")
         if not isinstance(reasoning_effort, str):