Callback Model

Vektra builder callbacks have two forms:

1. Standard on_click, on_change, on_focus, and on_blur forms receive App-level callbacks and suit logic that does not need host Entity state.
2. on_click_in, on_change_in, on_focus_in, and on_blur_in receive a &Context<T>. They use Context::listener internally, so handlers can mutate &mut T and call cx.notify().

_in is Vektra's host-Entity binding convention. It is neither DOM capture/bubble nor GPUI's subtree on_focus_in semantics. Component callbacks execute synchronously.

After the host Entity is destroyed, the weak reference held by Context::listener no longer upgrades, so the callback safely stops running. Start asynchronous work from an Entity-bound callback with GPUI task APIs and let the host own task lifecycle.

Changeable<T> uses on_change for a user-requested next controlled value. It carries no ClickEvent and does not imply that the component committed state.

Input is the explicit exception: its caller-owned InputState also implements EventEmitter<InputEvent>. Builder callbacks and Changed, Focused, Blurred, and Submitted events share one semantic path rather than two editing implementations. Programmatic set_value, clear, and reset never produce Changed.