A bare `measureElement()` called inside `watchPostEffect` reads layout BEFORE
the commit scheduler's post-flush `calculateLayout` runs, so it returns an
uncomputed value (NaN for computed dimensions), not the current size. The JSDoc
previously recommended that exact broken call site.
Align the guidance to vue-tui's real post-flush timing: defer the read with
`nextTick(() => measureElement(ref.value))` — the pattern `useBoxMetrics` itself
uses — or read from an input/timer callback that fires after a flush; prefer
`useBoxMetrics` for reactive metrics. Also correct the stale claim that a
pre-layout read returns `{0,0}` (it returns NaN for an attached-but-uncomputed
node; `{0,0}` is only the detached case).
Adds a characterization test pinning bare-watchPostEffect = NaN vs
nextTick = real width (80), guarding against regressing to the old advice.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Yunfei He
c05cb5df36