nest_asyncio.apply() breaks Python 3.14: asyncio task corruption → HTTP 500 on every static-asset request

[pidefrem]

Bug

chainlit run fails on Python 3.14. The browser shows a white page because
every static-asset request (/assets/*.js, /public/*) returns HTTP 500:

anyio.NoEventLoopError: Not currently running on any asynchronous event loop.
Available async backends: asyncio, trio

Root cause

chainlit/cli/__init__.py calls nest_asyncio.apply() at module import time.
nest_asyncio ≤ 1.6.0 patches loop.run_until_complete() via:

asyncio.ensure_future(future, loop=self)   # nest_asyncio 1.6.0, line 88

The loop= keyword was deprecated in Python 3.8 and removed in Python 3.14
(bpo-39529). On Python 3.14 this silently
corrupts asyncio task registration: asyncio.current_task() returns None
inside running coroutines.

The failure chain:

1. chainlit run → import chainlit.cli → nest_asyncio.apply() at module level
2. nest_asyncio patches the loop using the removed loop= kwarg → tasks not registered
3. Browser requests /assets/index-*.js
4. FileResponse.__call__ → anyio.to_thread.run_sync(os.stat, path)
5. anyio → sniffio.current_async_library() → asyncio.current_task() → None
6. anyio.NoEventLoopError → HTTP 500 → no JS → white page

Note: nest_asyncio has not been updated since 2023 and is effectively
unmaintained.

Fix

Remove nest_asyncio entirely. asyncio.run(start()) at the bottom of
run_chainlit() is a top-level entry point — it does not run inside any other
event loop and has never needed re-entrant loop support. The existing comment
in the source ("Not sure if it is necessary...") confirms this was always
uncertain.

A PR with the fix, updated pyproject.toml, regenerated lockfile, and a
regression test is ready: #2953

Related

• Closes chainlit Python 3.14 anyio.NoEventLoopError: Not currently running on any asynchronous event loop. Available async backends: asyncio, trio #2767 (bot-closed without fixing the root cause)
• nest_asyncio loop= removal: https://bugs.python.org/issue39529
• Python 3.14 what's new: https://docs.python.org/3.14/whatsnew/3.14.html

[github-actions]

This issue is stale because it has been open for 14 days with no activity.

[pidefrem]

This is still a valid bug — nest_asyncio.apply() corrupts asyncio tasks on Python 3.14, causing HTTP 500s on static-asset requests. A fix is ready and open in #2953 (removes nest_asyncio, makes chat-profile config resolution async-safe). Could a maintainer triage this / review the PR? Thanks! 🙏