build --html leaves background processes behind #2484
Description
On Ubuntu 25.10 Jupyter book with build --html leaves a background server process hanging, which can cause a large memory usage.
Full reproducer:
ps aux | grep server.js
# anton 1318358 0.0 0.0 10012 1572 pts/5 S+ 21:29 0:00 grep --color=auto server.js
mkdir ~/tmp/jb_background_process && cd ~/tmp/jb_background_process
pixi init && pixi add jupyter-book
touch index.md
pixi run jupyter book init --write-toc
pixi run jupyter book build --html
pixi run jupyter book build --html
pixi run jupyter book build --html
ps aux | grep server.js
# anton 1319074 0.0 0.0 3044 1476 pts/5 S 21:31 0:00 sh -c node ./server.js
# anton 1319075 2.9 1.7 1923556 266444 pts/5 Sl 21:31 0:00 node ./server.js
# anton 1319206 0.0 0.0 3044 1524 pts/5 S 21:31 0:00 sh -c node ./server.js
# anton 1319207 3.2 1.7 1923276 266236 pts/5 Sl 21:31 0:00 node ./server.js
# anton 1319467 0.0 0.0 3044 1500 pts/5 S 21:32 0:00 sh -c node ./server.js
# anton 1319468 36.4 1.7 1923248 265696 pts/5 Sl 21:32 0:00 node ./server.js
# anton 1319534 0.0 0.0 10012 1636 pts/5 S+ 21:32 0:00 grep --color=auto server.js