Zoom fix: The zoom handler was being completely removed during the
fit-to-view animation (svg.on('.zoom', null)), which meant D3's
transition dispatched zoom events that nobody handled — so `g` never
got its transform updated during the animation. The view stayed stuck
at the old scale until the user scrolled again.
Fix: Keep handleZoom active during commit animation. When isCommitting
is true, it only applies the visual transform (g.attr('transform'))
and skips threshold logic. This lets D3's transition smoothly animate
`g` to the fit-to-view position.
Branch handles: Removed the occupied-position check. In a real metro,
stations can be shared between lines (interchanges). Now all 3 branch
handles always appear. Ghost preview shows "interchange" label when
targeting an occupied position.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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