It seems that the screen width that is written into the Z-machine header (address 0x21) is the actual width % 256. This causes problems for a game or library that tries to adapt the content to the screen width, or judge if the game is even playable.
I can't find anything in the standard saying what the terp should do in this case. Setting the width to 255 may be the best, and most likely to work with existing games.
It seems that the screen width that is written into the Z-machine header (address 0x21) is the actual width % 256. This causes problems for a game or library that tries to adapt the content to the screen width, or judge if the game is even playable.
I can't find anything in the standard saying what the terp should do in this case. Setting the width to 255 may be the best, and most likely to work with existing games.