· Interface
A real superellipse, drawn by a paint worklet
The composer's curve is a genuine squircle rather than a rounded rectangle, painted by a worklet because the CSS property that would do it is inert on this runtime.
corner-shape: squircle is inert in the Chromium this app ships on. A surface that declares it and nothing else renders a plain rounded rect next to a composer wearing a real curve, which is worse than not having asked.
A paint worklet draws the curve. Any surface declaring it is listed in the worklet's rule, and a test enforces the pairing so the two cannot drift.
Where the signature goes, the hairline ring comes off. A ring traced around a large radius is the one thing that reliably makes the radius read as a mistake rather than a decision. The prompter's lift is cast from the painted curve rather than from its bounding box, which is what had made the shadow look detached.
It belongs on a panel the eye rests in: the composer, a fenced code block, a commit card, an install card. It does not belong on a routine list row, a menu, a chip, or anything else whose job is to be counted rather than read.