Width was initialized to 480px on every render, so clicking a different
workspace node (which re-mounts SidePanel) discarded any resize the user
had done.
Fix:
- localStorage-backed useState initializer (SSR-safe typeof window guard)
- Validates the stored value: must be a finite integer ≥ 320px
- Persists the width in the mouseUp handler via a widthRef that stays in
sync with the live drag value — avoids spamming localStorage on every
pixel during the drag
- Extra guard: onMouseUp bails early if not actually dragging (prevents
spurious saves on unrelated window mouseup events)
- Named constants replace magic numbers 480 / 320
Tests: 5 new cases in SidePanel.tabs.test.tsx — default fallback, valid
saved value, too-small saved value, NaN saved value, drag-persist roundtrip.
Closes#425
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
966920355a