fix(vnc): detect Xvfb via /tmp/.X11-unix socket, not ps regex

[luxles]

Bug

plugins/vnc/vnc-watcher.sh detects the Camoufox Xvfb display with:

FOUND=$(ps -eo args= 2>/dev/null | awk -v res="$VNC_RESOLUTION" '
    /\\/Xvfb :[0-9]+/ && index($0, res) {
      for (i=1;i<=NF;i++) if ($i ~ /^:[0-9]+$/) { print $i; exit }
    }
  ' | head -1)

This regex requires the literal :N token (e.g. Xvfb :0 ...) in Xvfb's ps args.

But Camoufox launches Xvfb with -displayfd 3 (e.g. Xvfb -displayfd 3 -screen 0 1920x1080x24 ...). In that mode the display number is not present as a literal :N token in ps args — it is allocated by Xvfb and exposed only as the /tmp/.X11-unix/X0 socket.

→ With -displayfd 3, FOUND is always empty → the watcher never launches x11vnc → port 5900 never listens, VNC stays black.

Fix

Detect the display via the /tmp/.X11-unix/X* socket (mode-independent — works for both :N literal launches and -displayfd N launches):

FOUND=""
for sock in /tmp/.X11-unix/X*; do
  [ -e "$sock" ] || continue
  DISP_NUM=$(basename "$sock" | sed 's/^X//')
  echo "$DISP_NUM" | grep -qE '^[0-9]+$' || continue
  # Crucial fix: verify it's a socket, not the X11-unix directory
  [ -S "$sock" ] || continue
  FOUND=":$DISP_NUM"
  break
done

Equivalent result to the original regex (yields :0), but also works when Xvfb is started with -displayfd 3.

Verification

• Environment: Camoufox launched as Xvfb -displayfd 3 -screen 0 1920x1080x24 ...
• Before fix: watcher log stops at VNC watcher started -- will attach x11vnc when Camoufox's Xvfb appears; 5900 never listens.
• After fix: when /tmp/.X11-unix/X0 appears, FOUND=:0, x11vnc launches, 5900 listens, noVNC (6080) connects.

Scope note (no overclaim)

This PR fixes only the display-detection regex not matching the -displayfd 3 launch mode.
Note there is a separate, orthogonal issue: some locally-built camofox-browser:135.0.1-x86_64 images fail to start the browser at all in certain environments (noVNC missing from image, UBO addon download fails, cannot open display: [object Promise] = the await VirtualDisplay.get() bug). That is a different root cause and is not addressed by this PR.

Related

• Symptom issue: Can't run and get VNC to work #5805 ("Can't run and get VNC to work" — Xvfb starts but 5900 never listens, exactly this bug's symptom)
• Adjacent fix fix: re-attach x11vnc after it dies on browser restart #6549 (re-attach x11vnc after browser restart) still relies on the ps regex; under -displayfd 3 its FOUND is also empty, so its fix does not take effect. Suggest adopting socket detection there too once this merges.

[skyfallsin]

Thank you — the -displayfd attachment fix has shipped in v1.12.1. The released implementation keeps the socket-based behavior while mapping the socket back to the watcher-owned Xvfb PID, so multiple Camofox servers cannot attach to each other’s displays. It also includes same-display x11vnc recovery and a Linux smoke test.

Included via commit 50b5031 with co-author credit.