A malformed custom borderStyle OBJECT (e.g. `{ topLeft, topRight }` missing
`top`) — or a truthy non-string non-object value (e.g. a number from a JS
caller) — bypassed assertBoxValid's render-time check, which only shape-checked
the STRING form. It reached drawBorder, passed the `if (!chars)` guard, and
threw `Cannot read properties of undefined (reading 'repeat')` deep in the
post-flush PAINT pass — wedging Vue's scheduler instead of surfacing a
recoverable error, exactly the failure mode box-validate.ts exists to prevent.
Resolve borderStyle to a BoxStyle the same way paint's drawBorder does (string
-> cliBoxes[name], object -> directly), then shape-check the result: every one
of the 8 glyphs paint reads (top/bottom/left/right + the four corners) must be
a string. Any invalid value now throws a clean error AT RENDER, caught by the
error boundary — like the existing unknown-string case. The string case keeps
its "Unknown borderStyle:" wording; the object/non-string case uses "Invalid
borderStyle:".
Test-first: borders.test.tsx now asserts a malformed object, a number, each
individually-missing glyph, and a present-but-non-string glyph all reject at
render (not the opaque paint TypeError), and a complete custom object still
paints a border.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Yunfei He
df843b67fe