fix(shared): report border-box dimensions from useResize

[joshuaellis]

useResize reported contentRect, which excludes padding and border — so consumers measuring a padded element got back the inner content size instead of the rendered box. The fix observes elements with { box: 'border-box' } and reads borderBoxSize, with a contentRect fallback for entries that lack it. inlineSize/blockSize are flipped back to width/height for vertical and sideways writing modes so the public shape is unchanged.

Tests

New real-DOM test in resizeElement.test.ts exercises a padded + bordered element and a vertical writing-mode element against a real ResizeObserver.

Closes #2288
Closes #2419

[changeset-bot]

🦋 Changeset detected

Latest commit: 94eba37

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@react-spring/shared	Patch
@react-spring/animated	Patch
@react-spring/core	Patch
@react-spring/mock-raf	Patch
@react-spring/parallax	Patch
@react-spring/rafz	Patch
@react-spring/types	Patch
@react-spring/konva	Patch
@react-spring/native	Patch
@react-spring/three	Patch
@react-spring/web	Patch
@react-spring/zdog	Patch

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Project	Deployment	Actions	Updated (UTC)
react-spring	Ready	Preview	May 21, 2026 7:02pm