Import time signal handler install crashes from non-main threads such as marimo

[ntnadkarni]

Description

cwsandbox/_cleanup.py calls _install_handlers() at module load, which calls signal.signal(). That only works on the main thread, so simply importing cwsandbox from a worker thread crashes with ValueError: signal only works in main thread of the main interpreter.

import threading
threading.Thread(target=lambda: __import__("cwsandbox")).start()
# ValueError: signal only works in main thread of the main interpreter

marimo executes the with app.setup: block from a worker thread, so any marimo notebook that imports cwsandbox in setup fails before the first cell renders.

This is not a hard blocker. For now I have a workaround in my marimo notebook that catches the ValueError and restores the original just wanted to file this in case it impacts others

Steps to reproduce

import marimo
app = marimo.App()

with app.setup:
    from cwsandbox import Sandbox  

Expected behavior

Import should succeed.

Actual behavior

ValueError: signal only works in main thread of the main interpreter

cwsandbox version

0.24.0

Python version

3.13.9

Operating system

No response

Additional context

No response