Method startAutoScroll

lib/selection-manager.ts:691–739

* Start auto-scrolling in the given direction

(direction: number)

   * Start auto-scrolling in the given direction
   */
  private startAutoScroll(direction: number): void {
    // Don't restart if already scrolling in same direction
    if (this.autoScrollInterval !== null && this.autoScrollDirection === direction) {
      return;
    }

    // Stop any existing scroll
    this.stopAutoScroll();

    this.autoScrollDirection = direction;

    // Start scrolling interval
    this.autoScrollInterval = setInterval(() => {
      if (!this.isSelecting) {
        this.stopAutoScroll();
        return;
      }

      // Scroll the terminal to reveal more content in the direction user is dragging
      // autoScrollDirection: -1 = dragging up (wants to see history), 1 = dragging down (wants to see newer)
      // scrollLines convention: negative = scroll up into history, positive = scroll down to newer
      // So direction maps directly to scrollLines sign
      const scrollAmount = SelectionManager.AUTO_SCROLL_SPEED * this.autoScrollDirection;
      (this.terminal as any).scrollLines(scrollAmount);

      // Extend selection in the scroll direction
      // Key insight: we need to EXTEND the selection, not reset it to viewport edge
      if (this.selectionEnd) {
        const dims = this.wasmTerm.getDimensions();
        if (this.autoScrollDirection < 0) {
          // Scrolling up - extend selection upward (decrease absoluteRow)
          // Set to top of viewport, but only if it extends the selection
          const topAbsoluteRow = this.viewportRowToAbsolute(0);
          if (topAbsoluteRow < this.selectionEnd.absoluteRow) {
            this.selectionEnd = { col: 0, absoluteRow: topAbsoluteRow };
          }
        } else {
          // Scrolling down - extend selection downward (increase absoluteRow)
          // Set to bottom of viewport, but only if it extends the selection
          const bottomAbsoluteRow = this.viewportRowToAbsolute(dims.rows - 1);
          if (bottomAbsoluteRow > this.selectionEnd.absoluteRow) {
            this.selectionEnd = { col: dims.cols - 1, absoluteRow: bottomAbsoluteRow };
          }
        }
      }

      this.requestRender();
    }, SelectionManager.AUTO_SCROLL_INTERVAL);
  }

  /**
   * Stop auto-scrolling