Tool event listener API

This page demonstrates best-practice event subscriptions for integrating the toolkit into larger apps (e.g. custom topbars, side panels, and state stores).

Two event surfaces:

• Project hooks (recommended): subscribe with tk.on(name, fn) / tk.off(name, fn). This is equivalent to tk.paperScope.project.on/off, but avoids exposing Paper.js internals in your app code.
• Toolkit hooks (optional): subscribe with tk.addHandler(name, fn) / tk.removeHandler(name, fn). Enable emission via new AnnotationToolkit(viewer, { events: { toolkit: true } }).

Tip: always unsubscribe on teardown/unmount to prevent listener buildup.