feat(providers): support DeepSeek Responses API (#5197)

tests/providers/test_openai_responses.py

@@ -150,6 +150,22 @@ class TestConvertMessages:
         assert items[0]["content"][0]["type"] == "output_text"
         assert items[0]["content"][0]["text"] == "I'll help"
 
+    def test_preserves_deepseek_reasoning_content(self):
+        _, items = convert_messages([
+            {"role": "assistant", "reasoning_content": "think first", "content": "answer"},
+        ], preserve_reasoning=True)
+
+        assert items == [
+            {"type": "reasoning", "content": "think first"},
+            {
+                "type": "message",
+                "role": "assistant",
+                "content": [{"type": "output_text", "text": "answer"}],
+                "status": "completed",
+                "id": "msg_0",
+            },
+        ]
+
     def test_assistant_empty_content_skipped(self):
         _, items = convert_messages([{"role": "assistant", "content": ""}])
         assert len(items) == 0
@@ -539,6 +555,22 @@ class TestParseResponseOutput:
         assert result.content == "42"
         assert result.reasoning_content == "I think therefore I am."
 
+    def test_deepseek_reasoning_content_extracted(self):
+        resp = {
+            "output": [
+                {"type": "reasoning", "content": "think first"},
+                {"type": "message", "content": [
+                    {"type": "output_text", "text": "answer"},
+                ]},
+            ],
+            "status": "completed", "usage": {},
+        }
+
+        result = parse_response_output(resp)
+
+        assert result.content == "answer"
+        assert result.reasoning_content == "think first"
+
     def test_empty_output(self):
         resp = {"output": [], "status": "completed", "usage": {}}
         result = parse_response_output(resp)
@@ -1633,6 +1665,30 @@ class TestConsumeSdkStream:
         _, _, _, _, reasoning = await consume_sdk_stream(stream())
         assert reasoning == "thinking..."
 
+    @pytest.mark.asyncio
+    async def test_deepseek_reasoning_text_streamed(self):
+        events = [
+            MagicMock(type="response.reasoning_text.delta", delta="step 1 "),
+            MagicMock(type="response.reasoning_text.delta", delta="step 2"),
+            MagicMock(type="response.reasoning_text.done", text="step 1 step 2"),
+        ]
+        emitted: list[str] = []
+
+        async def stream():
+            for event in events:
+                yield event
+
+        async def on_reasoning_delta(delta: str) -> None:
+            emitted.append(delta)
+
+        _, _, _, _, reasoning = await consume_sdk_stream(
+            stream(),
+            on_reasoning_delta=on_reasoning_delta,
+        )
+
+        assert reasoning == "step 1 step 2"
+        assert emitted == ["step 1 ", "step 2"]
+
     @pytest.mark.asyncio
     async def test_error_event_raises(self):
         ev = MagicMock(type="error", error="rate_limit_exceeded")