fix: use reasoning_content for Open WebUI streaming

Use DeepSeek R1 format (reasoning_content field) instead of <think>
tags in content. Open WebUI now renders thinking as proper
collapsible blocks instead of broken escaped HTML.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/chat/test_streaming_wrapper.py

@@ -4,7 +4,7 @@ Tests for chat completions streaming wrapper.
 Tests that the wrapper correctly:
 - Wraps Responses API
 - Enables reasoning automatically
-- Converts reasoning to <think> tags
+- Streams reasoning via reasoning_content field (DeepSeek R1 format)
 - Streams both reasoning and content
 """
 import json
@@ -17,7 +17,7 @@ from src.chat import constants
 @pytest.mark.unit
 @pytest.mark.asyncio
 async def test_streaming_wrapper_enables_reasoning(async_client: AsyncClient):
-    """Test that streaming wrapper automatically enables reasoning."""
+    """Test that streaming wrapper automatically enables reasoning via reasoning_content."""
     request_data = {
         "model": "lorem-tester",
         "messages": [
@@ -27,7 +27,7 @@ async def test_streaming_wrapper_enables_reasoning(async_client: AsyncClient):
     }
 
     chunks_received = []
-    think_tags_found = False
+    reasoning_content_found = False
 
     async with async_client.stream(
         "POST",
@@ -51,12 +51,12 @@ async def test_streaming_wrapper_enables_reasoning(async_client: AsyncClient):
                     chunk = json.loads(data_str)
                     chunks_received.append(chunk)
 
-                    # Check for <think> tags in delta content
+                    # Check for reasoning_content in delta (DeepSeek R1 format)
                     if "choices" in chunk and len(chunk["choices"]) > 0:
                         delta = chunk["choices"][0].get("delta", {})
-                        content = delta.get("content")
-                        if content and ("<think>" in content or "</think>" in content):
-                            think_tags_found = True
+                        reasoning = delta.get("reasoning_content")
+                        if reasoning:
+                            reasoning_content_found = True
 
                 except json.JSONDecodeError:
                     pass
@@ -64,14 +64,14 @@ async def test_streaming_wrapper_enables_reasoning(async_client: AsyncClient):
     # Should have received chunks
     assert len(chunks_received) > 0
 
-    # Should have found <think> tags (reasoning enabled automatically)
-    assert think_tags_found, "Expected <think> tags in streaming output"
+    # Should have found reasoning_content (reasoning enabled automatically)
+    assert reasoning_content_found, "Expected reasoning_content in streaming output"
 
 
 @pytest.mark.unit
 @pytest.mark.asyncio
 async def test_streaming_wrapper_reasoning_before_content(async_client: AsyncClient):
-    """Test that reasoning (<think> tags) comes before actual content."""
+    """Test that reasoning_content comes before regular content."""
     request_data = {
         "model": "lorem-tester",
         "messages": [
@@ -80,10 +80,7 @@ async def test_streaming_wrapper_reasoning_before_content(async_client: AsyncCli
         "stream": True
     }
 
-    all_content = []
-    found_think_opening = False
-    found_think_closing = False
-    found_content_after_think = False
+    chunk_types = []  # Track order: 'reasoning' or 'content'
 
     async with async_client.stream(
         "POST",
@@ -106,28 +103,22 @@ async def test_streaming_wrapper_reasoning_before_content(async_client: AsyncCli
                     chunk = json.loads(data_str)
                     if "choices" in chunk and len(chunk["choices"]) > 0:
                         delta = chunk["choices"][0].get("delta", {})
-                        content = delta.get("content", "")
-                        if content:
-                            all_content.append(content)
+                        reasoning = delta.get("reasoning_content")
+                        content = delta.get("content")
 
-                            if "<think>" in content:
-                                found_think_opening = True
-                            if "</think>" in content:
-                                found_think_closing = True
-                            # Content after closing think tag
-                            if found_think_closing and content.strip() and "<think>" not in content and "</think>" not in content:
-                                found_content_after_think = True
+                        if reasoning:
+                            chunk_types.append("reasoning")
+                        if content:
+                            chunk_types.append("content")
 
                 except json.JSONDecodeError:
                     pass
 
-    # Verify ordering
-    full_text = "".join(all_content)
-    if found_think_opening and found_think_closing:
-        # Reasoning should come before main content
-        think_start = full_text.index("<think>")
-        think_end = full_text.index("</think>")
-        assert think_start < think_end, "Opening <think> should come before closing </think>"
+    # Verify reasoning comes before content
+    if "reasoning" in chunk_types and "content" in chunk_types:
+        first_reasoning = chunk_types.index("reasoning")
+        first_content = chunk_types.index("content")
+        assert first_reasoning < first_content, "reasoning_content should come before content"
 
 
 @pytest.mark.unit