fix: wrap markitdown PDF processing in asyncio.to_thread (#8614)

MarkItDown.convert() does blocking file I/O and CPU-intensive PDF parsing.
This was blocking the event loop during file uploads.

Now wraps the entire markitdown pipeline (tempfile write, convert, cleanup)
in asyncio.to_thread() to run in thread pool.

🐾 Generated with [Letta Code](https://letta.com)

Co-authored-by: Letta <noreply@letta.com>

letta/services/file_processor/parser/markitdown_parser.py

@@ -28,6 +28,8 @@ class MarkitdownFileParser(FileParser):
     @trace_method
     async def extract_text(self, content: bytes, mime_type: str) -> OCRResponse:
         """Extract text using markitdown."""
+        import asyncio
+
         try:
             # Handle simple text files directly
             if is_simple_text_mime_type(mime_type):
@@ -49,31 +51,37 @@ class MarkitdownFileParser(FileParser):
 
             logger.info(f"Extracting text using markitdown: {self.model}")
 
-            # Create temporary file to pass to markitdown
-            with tempfile.NamedTemporaryFile(delete=False, suffix=self._get_file_extension(mime_type)) as temp_file:
-                temp_file.write(content)
-                temp_file_path = temp_file.name
+            # Run CPU/IO-intensive markitdown processing in thread pool to avoid blocking event loop
+            def blocking_markitdown_convert():
+                # Create temporary file to pass to markitdown
+                with tempfile.NamedTemporaryFile(delete=False, suffix=self._get_file_extension(mime_type)) as temp_file:
+                    temp_file.write(content)
+                    temp_file_path = temp_file.name
 
-            try:
-                md = MarkItDown(enable_plugins=False)
-                result = md.convert(temp_file_path)
+                try:
+                    md = MarkItDown(enable_plugins=False)
+                    result = md.convert(temp_file_path)
+                    return result.text_content
+                finally:
+                    # Clean up temporary file
+                    os.unlink(temp_file_path)
 
-                return OCRResponse(
-                    model=self.model,
-                    pages=[
-                        OCRPageObject(
-                            index=0,
-                            markdown=result.text_content,
-                            images=[],
-                            dimensions=None,
-                        )
-                    ],
-                    usage_info=OCRUsageInfo(pages_processed=1),
-                    document_annotation=None,
-                )
-            finally:
-                # Clean up temporary file
-                os.unlink(temp_file_path)
+            # Run blocking operations in thread pool
+            text_content = await asyncio.to_thread(blocking_markitdown_convert)
+
+            return OCRResponse(
+                model=self.model,
+                pages=[
+                    OCRPageObject(
+                        index=0,
+                        markdown=text_content,
+                        images=[],
+                        dimensions=None,
+                    )
+                ],
+                usage_info=OCRUsageInfo(pages_processed=1),
+                document_annotation=None,
+            )
 
         except Exception as e:
             logger.error(f"Markitdown text extraction failed: {str(e)}")