The "Custom address" slug field sized its leftSection with a
character-count heuristic (label.length * 7 + 12), which over-estimated
the real width of the small dimmed domain prefix and left an ugly empty
gap between "docs.../l/" and the input text.
- Measure the real prefix width via a ref + useLayoutEffect (scrollWidth)
and feed it to leftSectionWidth so the slug sits flush against the
prefix, regardless of host length or font metrics.
- Restyle the prefix as an attached addon: subtle background, a right
divider border and input-matching left corner radii.
- Minor spacing tidy: description mb 4->6, action buttons mt xs->sm.
No behavior change: validation, availability probe, save/remove and the
reassign modal are untouched.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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