Function jumpBy

src/components/ScrollKeybindingHandler.tsx:834–847

(s: ScrollBoxHandle, delta: number)

// Target is relative to scrollTop+pendingDelta so a jump mid-wheel-burst
// lands where the wheel was heading.
export function jumpBy(s: ScrollBoxHandle, delta: number): boolean {
  const max = Math.max(0, s.getScrollHeight() - s.getViewportHeight());
  const target = s.getScrollTop() + s.getPendingDelta() + delta;
  if (target >= max) {
    // Eager-write scrollTop so follow-scroll sees followDelta=0. Callers
    // that ran translateSelectionForJump already shifted; scrollToBottom()
    // alone would double-shift via the render-phase sticky follow.
    s.scrollTo(max);
    s.scrollToBottom();
    return true;
  }
  s.scrollTo(Math.max(0, target));
  return false;
}

// Wheel-down past maxScroll re-enables sticky so wheeling at the bottom
// naturally re-pins (matches typical chat-app behavior). Returns the