Individual stroke widths shipped with a `:stroke-per-side` boolean on every
stroke, telling the renderer and the CSS generator whether the four
per-side widths were meaningful. Comparing the sides answers that on its
own, so the attribute was later dropped from the closed stroke schema
and the toggle became ephemeral editor state.
Files written between those two changes still carry the attribute, and
the closed schema rejects the unknown key, so loading such a file fails
`check-file-data` with a `:malli.core/extra-key` error and surfaces as
an internal error in the editor.
Add migration `0030-remove-stroke-per-side-attr`, which drops the
attribute from every stroke of every page and component shape. The
per-side widths are the saved design data and are kept untouched, so a
file whose boolean was `true` renders exactly as before.
The migration is naturally idempotent and a no-op for files that never
carried the attribute, since `dissoc` on a map without the key returns
an equal map.
Cover it with tests for the schema rejection, the per-side and global
widths surviving, component shapes, idempotency, and the run through
`migrate-file`.
Closes#11943
AI-assisted-by: space-bunny-free
b890b94d27