Add detach_process option to spawn

[imstevenpmwork]

Related Discussion

For more context, see this thread:
https://discord.com/channels/1062300748202921994/1354497232103145642
Related to: 1942b43

What’s New

This update introduces a detach_process option for the spawn() method in the Viewer (available in Rust, Python, and C++).

Why It Matters

This gives client code control over whether the Viewer runs independently of the parent process or remains tied to it. Keeping it attached ensures the Viewer closes when the parent process terminates with SIGINT. Detaching (default behavior) allows it to persist if needed.

While this achieves the desired functionality, a future improvement could be adding a proper close() method to gracefully shut down the Viewer context.

Note on Web Support

This change wasn’t applied to the web API since I'm not sure how process management behaves there.

How it was tested?

(Python only) Small edit to the minimal.py to evaluate the behavior

#!/usr/bin/env python3
"""Demonstrates the most barebone usage of the Rerun SDK."""

from __future__ import annotations

import sys

import numpy as np
import rerun as rr  # pip install rerun-sdk
import time


def main() -> None:
    # sanity-check since all other example scripts take arguments:
    assert len(sys.argv) == 1, f"{sys.argv[0]} does not take any arguments"

    rr.init("rerun_example_minimal")
    rr.spawn(detach_process=False)

    positions = np.vstack([xyz.ravel() for xyz in np.mgrid[3 * [slice(-10, 10, 10j)]]]).T
    colors = np.vstack([rgb.ravel() for rgb in np.mgrid[3 * [slice(0, 255, 10j)]]]).astype(np.uint8).T

    rr.log("my_points", rr.Points3D(positions, colors=colors, radii=0.5))
    time.sleep(10)  # CRTL+C here: Viewer process will exit


if __name__ == "__main__":
    main()

As expected, when detach_process=False if we send a SIGINT to the application, the Viewer exits and the PID assigned to it is retired.

[github-actions]

Hi! Thanks for opening this pull request.

Because this is your first time contributing to this repository, make sure you've read our Contributor Guide and Code of Conduct.

[emilk]

Looks great so far!

[emilk]

The CI failures seems unrelated. The C++ tests passes locally.