Root cause found via puppeteer inspection:
- trimBarWidth was 4px when renderTrim() ran
- That made calc(32.64% - 12px) = ~-10px, putting handles offscreen left
Modal element gets actual width AFTER appendChild + browser layout pass.
Original code called renderTrim() synchronously right after appendChild,
before the modal had real dimensions.
Fix:
1. Use ResizeObserver on trim-bar to re-render whenever it gets actual width
2. Also use double requestAnimationFrame as fallback (waits for layout)
Verified via puppeteer:
Before: leftStyle='calc(32.6443% - 12px)' but trimBarWidth=4
After: handles correctly positioned within visible bar
sebastjan
4f7d8df659