On some terminals prompt_toolkit's size probe reports the window one column
narrower than it really is, so the frame draws to columns-1 and the true
last column sits unused (selectable to the right of the border). Wrap the
real terminal output in _WidthExtendedOutput, which reports columns+1 from
get_size(); since the renderer and the frame compositor both key off that,
the final column now gets drawn.
Gated behind _RECLAIM_LAST_COLUMN (env MESHTERM_FULL_WIDTH=0 to disable) so
it can be turned off on a terminal whose probe is already correct — there
the extra column would fall off-screen and wrap — and eventually promoted
to a user setting. Test-supplied outputs are never wrapped, so headless
rendering keeps its exact size.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>