Drag sessions

startPointerDragSession(options): PointerDragSessionHandle

Owns one pointer gesture: immediate capture, movement threshold, Escape and lost-capture cancellation, and exactly-once teardown.

interface PointerDragSessionOptions {
  element: HTMLElement;
  event: PointerEvent;
  threshold?: number; // pixels before the drag starts, default 0
  documentClass?: string; // set on the document while dragging
  elementAttribute?: string; // set on element while dragging
  suppressClick?: boolean; // swallow the release click once started
  onStart?(): void;
  onMove(clientX: number, clientY: number, event: PointerEvent): void;
  onFinish(
    result: "commit" | "cancel",
    started: boolean,
    event: PointerEvent | null
  ): void;
}

interface PointerDragSessionHandle {
  cancel(): void;
}

suppressClick keeps a dropped button from also being pressed. Keyboard clicks still go through.

The other drag exports (startDragSession, SlidingReorder, resolveDropIndex, the insertion-line and ghost helpers) drive the package's own docks, tabs and trees.