0003 Filters and actions

Events report what happened. Hooks let extensions change how it happens.

• Filters transform a value through a priority-ordered pipeline (applyFilters(name, value, ...args)).

• Actions run callbacks at a named point (doAction(name, ...args)).

• Priority defaults to 10 (lower runs first) and ties keep registration order, like WordPress.

• Every registration has a namespace and a disposer. A plugin's hooks are removed when it is disposed.

• A throwing callback is isolated and reported; the pipeline continues with the last good value. Strict mode rethrows. Recursion is bounded.

• Hooks are synchronous inside transactions and rendering; async variants serve service pipelines.

• Names and signatures are declared by augmenting FilterHooks and ActionHooks, so typed hooks are checked at compile time; undeclared names remain usable with unknown types.