perf(backend): offload blocking calls in async paths to threads (#26381)

Audit of asyncio.sleep vs time.sleep and event-loop-blocking calls:

- utils/plugin.py: run pip `install_frontmatter_requirements`
  (subprocess.check_call) via asyncio.to_thread in load_tool_module_by_id,
  load_function_module_by_id, and install_tool_and_function_dependencies.
- retrieval/utils.py: move the synchronous SSRF-guarded requests probe and
  loader.load() in get_content_from_url into a sync helper run via
  asyncio.to_thread.
- routers/audio.py: write uploaded audio to disk off the event loop in
  transcription().
- routers/pipelines.py: write uploaded pipeline file off the event loop in
  upload_pipeline().

The existing time.sleep call sites are all in genuinely synchronous
functions (sync requests/DB drivers/daemon threads) with async
counterparts that already use asyncio.sleep, so no time.sleep -> asyncio.sleep
changes were needed.


Claude-Session: https://claude.ai/code/session_01LXR5bYfsfSS42RGHQZu2Ta

Co-authored-by: Claude <noreply@anthropic.com>

backend/open_webui/routers/audio.py

@@ -1192,8 +1192,12 @@ async def transcription(
         if not os.path.realpath(file_path).startswith(os.path.realpath(file_dir)):
             raise ValueError('Invalid file path detected')
 
-        with open(file_path, 'wb') as f:
-            f.write(contents)
+        def _write_upload():
+            with open(file_path, 'wb') as f:
+                f.write(contents)
+
+        # Audio uploads can be large; write to disk off the event loop.
+        await asyncio.to_thread(_write_upload)
 
         try:
             metadata = None

backend/open_webui/routers/pipelines.py

@@ -1,3 +1,4 @@
+import asyncio
 import logging
 import os
 import shutil
@@ -236,9 +237,12 @@ async def upload_pipeline(
 
     response = None
     try:
-        # Save the uploaded file
-        with open(file_path, 'wb') as buffer:
-            shutil.copyfileobj(file.file, buffer)
+        # Save the uploaded file off the event loop (uploads can be large).
+        def _save_upload():
+            with open(file_path, 'wb') as buffer:
+                shutil.copyfileobj(file.file, buffer)
+
+        await asyncio.to_thread(_save_upload)
 
         url, key = await get_openai_connection(urlIdx)