[Bug]: HTML preview browsers are never stopped inside an LXC container after t3 browser setup, and pile up #27136

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

Server: HTML preview rendering (apps/server/src/htmlRender/headlessChrome.ts)

Steps to reproduce

1. Run the T3 Code server (t3 v0.1.1) on Ubuntu 24.04 inside an LXC container.
2. Run t3 browser setup. It writes /etc/apparmor.d/t3-chrome-headless-shell (flags=(unconfined), userns).
3. Use chats that render HTML previews for a few hours.
4. List chrome-headless-shell processes whose --user-data-dir is under /tmp/t3-html-preview-*.

Expected behavior

Each preview browser exits when its capture finishes.

Actual behavior

The t3-html-preview-* temp directory is removed, but the browser keeps running. After about 14 hours there were 7 orphaned browsers using 113 to 235 MB each, about 1.3 GB in total.

Every attempt to stop one returns EPERM:

• kill as the same user
• kill as root via sudo
• systemctl --user stop on its scope, which logs Failed to kill control group ... Permission denied
• aa-exec -p t3-chrome-headless-shell -- kill

A normal process started by the same user can be killed. The browsers run under the AppArmor label t3-chrome-headless-shell, and every sender was unconfined.

Impact

Each preview leaks a browser that can't be stopped, so memory grows until the container restarts.

Version or commit

t3 v0.1.1, chrome-headless-shell 154.0.8037.92

Environment

Ubuntu 24.04.4 LTS in an LXC container (systemd-detect-virt -c reports lxc), kernel 7.0.0-34-generic.

Logs or stack traces

systemd[3738]: app-org.chromium.Chromium-1051116.scope: Failed to kill control group /user.slice/user-1002.slice/user@1002.service/app.slice/app-org.chromium.Chromium-1051116.scope, ignoring: Permission denied

Guess at the cause (unconfirmed): AppArmor stacking in LXC blocks signals sent to a process under a different label, so the server's cleanup can't stop the browser.

Workaround

None found short of restarting the container.