An `all` composite gave up below half width, so "2027" in a font with
proportional digits (about 0.45) stayed sideways, while `digits` combined
the same run down to 1 / length.
A Western run no longer than a `digits` composite now squeezes as far as
one. Upright CJK and longer runs keep the half-width limit, since a
deeper squeeze makes full-width glyphs illegible.
AI-assisted-by: claude-opus-5-5
913e9633d9