The wrapper takes the xenia window's geometry from `xwininfo -root -children`
and crops the game surface out of it. Two things are wrong with that here, and
neither errors:
* `-children` lists only DIRECT children of the root, and openbox reparents the
game window — so the real one is not in that list at all;
* the app owns more than one window of class "xenia_canary" — an off-screen 10x10
helper as well as the 1280x745 game window — so `head -1` picked the 10x10 one.
Every grab came back a 10-pixel sliver, and nothing failed: `screen_id.py`
happily classified the sliver, the movie-skip heuristic fired on its noise, and
a whole session's worth of screen ids were meaningless. It also drove a stray
tap into the title screen's save-data probe, which crashed the guest.
Walk the full tree and take the largest xenia window by area, using its absolute
geometry (a reparented window's own +X+Y is relative to its frame).
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