Xorg failed to start with:
(EE) xf86OpenConsole: Cannot open virtual console 1 (Permission denied)
udev leaves console VTs as 620 root:tty — group tty has write-only, so
even a tty-group member can't open /dev/tty1 read+write (display managers
normally get this via logind seat ACLs, which a manually-started X
doesn't have). The session script now chowns the dedicated VT to
liveuser before starting X; the unit already Conflicts with getty@tty1 so
nothing else needs it.
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