fix(knowledge-store): read the commit subject out of content blocks

A reasoning model replies with a list of blocks rather than a string, so
stringifying it wrote the model's entire thinking into the revision's
commit message. Reuse the existing extractor, which keeps text and drops
reasoning.

surfsense_backend/app/agents/chat/multi_agent_chat/main_agent/middleware/knowledge_store_persistence/commit_message.py

@@ -7,6 +7,8 @@ import logging
 from collections.abc import Iterable, Mapping
 from typing import Any
 
+from app.tasks.chat.llm_history_normalizer import assistant_content_to_llm_text
+
 logger = logging.getLogger(__name__)
 
 _SYSTEM_PROMPT = (
@@ -71,9 +73,9 @@ async def generate_commit_message(
             ),
             timeout=_GENERATION_TIMEOUT_SECONDS,
         )
-        content = getattr(reply, "content", "")
-        if not isinstance(content, str):
-            content = str(content)
+        # A reasoning model answers in content blocks, so the subject has to be
+        # read out of them: ``str()`` on the list commits the model's thinking.
+        content = assistant_content_to_llm_text(getattr(reply, "content", ""))
         subject = content.strip().splitlines()[0].strip() if content.strip() else ""
         if subject:
             return subject

surfsense_backend/tests/unit/middleware/test_commit_message.py

@@ -50,6 +50,25 @@ async def test_uses_the_models_reply_as_subject():
     assert message == "docs: add meeting notes"
 
 
+async def test_a_reasoning_models_thinking_never_reaches_the_subject():
+    """Reasoning models answer in blocks; the shape below is a real reply."""
+
+    class _ReasoningModel:
+        async def ainvoke(self, _input, config=None, **kwargs):
+            return SimpleNamespace(
+                content=[
+                    {"type": "thinking", "thinking": "**Inferring commit message**"},
+                    {"type": "thinking", "thinking": " the user wants a leaf image"},
+                    "docs: add simple green leaf image prompt",
+                ]
+            )
+
+    message = await generate_commit_message(
+        _ReasoningModel(), writes={"documents/leaf.md": b"# Leaf"}, removes=[]
+    )
+    assert message == "docs: add simple green leaf image prompt"
+
+
 async def test_falls_back_deterministically_when_the_model_fails():
     message = await generate_commit_message(
         _BrokenModel(),