A bot crash leaves /tmp/.X99-lock behind; the next container start
hits "Server is already active for display 99" and the entrypoint
previously fell through with only a warning, so Chromium then died
with "Missing X server or $DISPLAY" in a tight crash loop. Remove
the stale lock up-front and fail hard if Xvfb still won't come up,
so the failure mode is "container won't start" rather than "bot
crashes forever".
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>