Fix X11 socket sticky bit setup

[linghengqian]

• Fixes /tmp/.X11-unix is missing the sticky bit #1122 .
• Fixes Update mode of .X11-unix directory to 01777 (sticky bit set) #1137 .
• Fix X11 socket sticky bit setup.

[linghengqian]

@ErEbusE If you have ideas, you should submit a new PR directly, instead of trying to make me guess about scenarios that can't be tested......

Of course I know about using xwayland as an Xserver, and I'm pretty sure that the existing GitHub gist has bugs.

[ErEbusE]

you're right

[benhillis]

Triage note (2026-05): Thanks — this is a real bug and the approach (treat /tmp/.X11-unix like a proper sticky-bit dir, log and continue on failure) is the right shape. A few small things on the next round:

1. The chmod failure log mentions "Xwayland may fail to start" but we keep running anyway — that''s correct, but please make sure the log line is consistent across the three branches (currently the EACCES branch says "Permission denied while checking" which reads like it''s about stat, not chmod).
2. There''s a related older PR Update mode of .X11-unix directory to 01777 (sticky bit set) #1137 that took a different approach (removing the /run/.X11-unix creation rather than fixing the /tmp/.X11-unix perms). I''ll close Update mode of .X11-unix directory to 01777 (sticky bit set) #1137 in favor of this one once we''re ready to merge.
3. Needs an internal buddy build to confirm there are no regressions on Wayland-only configurations where /tmp/.X11-unix is absent.

Will queue for review.

[linghengqian]

I'll wait for good news. After all, I'm not a Microsoft employee, so I'm not sure what I should do.