Add an error boundary event

Let's protect "Charge credit card" with an error boundary event.

How to add a boundary event

• Hover slowly over the "Charge credit card" task
• A small circle icon appears on the bottom edge of the task — that's the boundary event handle
• Click it to place an error boundary event on the task

Alternatively:

• Drag a boundary event shape from the palette
• Drop it directly onto the task — it snaps to the boundary

The boundary event should appear as a small circle with a lightning bolt (⚡) sitting on the edge of the task.

> 💡 The event sits *on* the task, not beside it. This visual attachment makes it clear which task this error handling belongs to.