Plan step 22, actions.md § Missing (Square-by-default button groups): M3
lists "Default shape | Round, square" as a button-group configuration and
neither `<x-button-group>` nor `<x-group>` had a `shape` prop, so a group
of square buttons still drew round outer corners.
`shape="square"` passes the square corner scale to every child through
`data-shape` and two new variables in groups.css: `--group-outer` is what
the two ends of a group round to (half the height when round, the corner
its inner edges take when square — M3's square table, 4/8/8/16/20dp), and
`--group-square`/`--group-square-pressed` give a standard group's buttons
the scale `<x-button shape="square">` draws. The selected rules keep
`--group-full`, so a selected button in a square group rounds: M3 has a
toggle inside a group swap shape on selection either way.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
