fix(cli,session): remove nest_asyncio, make chat-profile config async-safe

backend/chainlit/cli/__init__.py

@@ -4,13 +4,17 @@
 import sys
 
 import click
-import nest_asyncio
 import uvicorn
 
-# Not sure if it is necessary to call nest_asyncio.apply() before the other imports
-nest_asyncio.apply()
-
-# ruff: noqa: E402
+# nest_asyncio was intentionally removed (see https://github.com/Chainlit/chainlit/issues/2767).
+# nest_asyncio ≤ 1.6.0 patches loop.run_until_complete() via
+# asyncio.ensure_future(future, loop=self), where the ``loop=`` keyword was
+# deprecated in Python 3.8 and **removed in Python 3.14** (bpo-39529).
+# Applying it at import time silently corrupted asyncio task registration:
+# asyncio.current_task() returned None inside running coroutines, which
+# caused anyio.NoEventLoopError on every static-asset request (HTTP 500 /
+# white page) on Python 3.14.  The entry point asyncio.run(start()) is a
+# top-level call and has never needed re-entrant loop support.
 from chainlit.auth import ensure_jwt_secret
 from chainlit.cache import init_lc_cache
 from chainlit.config import (

backend/pyproject.toml

@@ -43,7 +43,6 @@ dependencies = [
     "syncer>=2.0.3,<3.0.0",
     "asyncer>=0.0.8,<0.1.0",
     "mcp>=1.11.0,<2.0.0",
-    "nest-asyncio>=1.6.0,<2.0.0",
     "click>=8.1.3,<9.0.0",
     "tomli>=2.0.1,<3.0.0",
     "pydantic>=2.7.2,<3",

backend/tests/test_cli.py

@@ -0,0 +1,33 @@
+"""Regression tests for chainlit.cli import behaviour.
+
+Ensures nest_asyncio is not imported by chainlit.cli.
+
+Background
+----------
+nest_asyncio ≤ 1.6.0 patches ``asyncio.BaseEventLoop.run_until_complete`` via
+``asyncio.ensure_future(future, loop=self)``.  The ``loop=`` keyword was
+deprecated in Python 3.8 and **removed in Python 3.14** (bpo-39529).  When
+``nest_asyncio.apply()`` ran at module-import time it silently corrupted asyncio
+task registration: ``asyncio.current_task()`` returned ``None`` inside running
+coroutines, causing ``anyio.NoEventLoopError`` on every static-asset request
+and a white screen for users on Python 3.14.
+
+See https://github.com/Chainlit/chainlit/issues/2767
+"""
+
+import chainlit.cli
+
+
+def test_nest_asyncio_not_in_cli_namespace():
+    """chainlit.cli must not expose nest_asyncio in its module namespace.
+
+    If ``import nest_asyncio`` is ever re-added to cli/__init__.py this test
+    will fail immediately, preventing the Python 3.14 regression from
+    being reintroduced.
+    """
+    assert not hasattr(chainlit.cli, "nest_asyncio"), (
+        "chainlit.cli exposes 'nest_asyncio' in its namespace. "
+        "Remove 'import nest_asyncio' and 'nest_asyncio.apply()' from "
+        "backend/chainlit/cli/__init__.py — nest_asyncio breaks Python 3.14 "
+        "via the removed loop= kwarg in asyncio.ensure_future (bpo-39529)."
+    )