Hooks

Hooks let applets communicate with each other safely. Three primitives:

Primitive	Use when	Pattern
Actions	Broadcasting events	Fire-and-forget, multiple listeners
Filters	Transforming data through handlers	Priority chain, each handler mutates
Calls	Typed request/response operations	One handler, one reply

Most applets use a mix. Use actions for notifications (“weather data updated”), filters for transforms (“format this temperature”), and calls for structured operations (“open this doc in the editor, return the opened path”).

Which one to pick?

• Does the caller need a reply?

  • Yes, and the semantics are “invoke this specific operation”: calls.
  • Yes, and the semantics are “pipe this value through everything listening”: filters.
  • No: actions.

• Is there exactly one sensible handler (e.g., “get the currently opened file”)?

  • Yes: calls.

• Can there be many listeners that all want to know about an event?

  • Yes: actions.

Capabilities

Capability	Grants
hooks:provide	Register action listeners, filter handlers, or call-hook handlers
hooks:consume	Fire actions, apply filters, invoke calls

Most applets that use hooks need both.