Function check

src/components/ScrollKeybindingHandler.tsx:741–784

()

    // scrolling, highlight walks up with the text). Keeping sticky also
    // avoids useVirtualScroll's tail-walk → forward-walk phantom growth.
    function check(): void {
      const s_0 = scrollRef.current;
      if (!s_0) {
        stop();
        return;
      }
      const top_0 = s_0.getViewportTop();
      const bottom_0 = top_0 + s_0.getViewportHeight() - 1;
      const sel_0 = selection.getState();
      // Pass the LAST-scrolled direction (not dirRef) so the anchor guard is
      // bypassed after shiftAnchor has clamped anchor toward row 0. Using
      // lastScrolledDirRef (survives stop()) lets autoscroll resume after a
      // brief mouse dip into the viewport. Same-direction only — a mouse
      // jump from below-bottom to above-top must stop, since reversing while
      // the scrolledOffAbove/Below accumulators hold the prior direction's
      // rows would duplicate text in getSelectedText. Reset on drag-finish
      // OR when both accumulators are empty: startSelection clears them
      // (selection.ts), so a new drag after a lost-release (isDragging
      // stuck true, the reason AUTOSCROLL_MAX_TICKS exists) still resets.
      // Safe: start() below re-records lastScrolledDirRef before its
      // early-return, so a mid-scroll reset here is instantly undone.
      if (!sel_0?.isDragging || sel_0.scrolledOffAbove.length === 0 && sel_0.scrolledOffBelow.length === 0) {
        lastScrolledDirRef.current = 0;
      }
      const dir_1 = dragScrollDirection(sel_0, top_0, bottom_0, lastScrolledDirRef.current);
      if (dir_1 === 0) {
        // Blocked reversal: focus jumped to the opposite edge (off-window
        // drag return, fast flick). handleSelectionDrag already moved focus
        // past the anchor, flipping selectionBounds — the accumulator is
        // now orphaned (holds rows on the wrong side). Clear it so
        // getSelectedText matches the visible highlight.
        if (lastScrolledDirRef.current !== 0 && sel_0?.focus) {
          const want = sel_0.focus.row < top_0 ? -1 : sel_0.focus.row > bottom_0 ? 1 : 0;
          if (want !== 0 && want !== lastScrolledDirRef.current) {
            sel_0.scrolledOffAbove = [];
            sel_0.scrolledOffBelow = [];
            sel_0.scrolledOffAboveSW = [];
            sel_0.scrolledOffBelowSW = [];
            lastScrolledDirRef.current = 0;
          }
        }
        stop();
      } else start(dir_1);
    }
    const unsubscribe = selection.subscribe(check);
    return () => {
      unsubscribe();