An inner <Box backgroundColor=""> inside an ancestor Box with a real bg clobbered
the inherited background (descendants rendered bare). vue used `?? inheritedBg`,
which only falls back for null/undefined — "" passed through. Ink keeps inheriting:
its provider uses a TRUTHY guard (Box.tsx:103 `if (backgroundColor)`), while the
fill uses the Box's OWN style (render-background.ts:11), so an empty-bg Box paints
no fill yet still passes the ancestor's bg down.
Split the single bg variable: the FILL uses the Box's own bg (falsy-guarded → empty
paints nothing), and the value THREADED to children is `ownBg ? ownBg : inheritedBg`
(truthy fallback → empty inherits the ancestor). A sized/bordered empty-bg inner box
therefore adds no own fill while its text still inherits — locked by a discriminator
test that fails the naive single-variable form.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Yunfei He
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