Function translateSelectionForJump

src/components/ScrollKeybindingHandler.tsx:413–446

(s: ScrollBoxHandle, delta: number)

  // still clears — its async pendingScrollDelta drain means the actual
  // delta isn't known synchronously (follow-up).
  function translateSelectionForJump(s: ScrollBoxHandle, delta: number): void {
    const sel = selection.getState();
    if (!sel?.anchor || !sel.focus) return;
    const top = s.getViewportTop();
    const bottom = top + s.getViewportHeight() - 1;
    // Only translate if the selection is ON scrollbox content. Selections
    // in the footer/prompt/StickyPromptHeader are on static text — the
    // scroll doesn't move what's under them. Same guard as ink.tsx's
    // auto-follow translate (commit 36a8d154).
    if (sel.anchor.row < top || sel.anchor.row > bottom) return;
    // Cross-boundary: anchor in scrollbox, focus in footer/header. Mirror
    // ink.tsx's Flag-3 guard — fall through without shifting OR capturing.
    // The static endpoint pins the selection; shifting would teleport it
    // into scrollbox content.
    if (sel.focus.row < top || sel.focus.row > bottom) return;
    const max = Math.max(0, s.getScrollHeight() - s.getViewportHeight());
    const cur = s.getScrollTop() + s.getPendingDelta();
    // Actual scroll distance after boundary clamp. jumpBy may call
    // scrollToBottom when target >= max but the view can't move past max,
    // so the selection shift is bounded here.
    const actual = Math.max(0, Math.min(max, cur + delta)) - cur;
    if (actual === 0) return;
    if (actual > 0) {
      // Scrolling down: content moves up. Rows at the TOP leave viewport.
      // Anchor+focus shift -actual so they track the content that moved up.
      selection.captureScrolledRows(top, top + actual - 1, 'above');
      selection.shiftSelection(-actual, top, bottom);
    } else {
      // Scrolling up: content moves down. Rows at the BOTTOM leave viewport.
      const a = -actual;
      selection.captureScrolledRows(bottom - a + 1, bottom, 'below');
      selection.shiftSelection(a, top, bottom);
    }
  }
  useKeybindings({
    'scroll:pageUp': () => {
      const s_0 = scrollRef.current;