# CatchHandler

A reactive complete-cause handler that produces fallback Fx output.

## Signatures

```ts
export type CatchHandler<E, A, E2, R2> = (cause: RefSubject.RefSubject<Cause.Cause<E>>) => Fx.Fx<A, E2, R2>;
```

## Why

Error boundaries can respond to failure, defect, or interruption without erasing cause structure.

## Ownership and lifetime

The catch manager invokes the handler inside a child Scope. That Scope owns the cause RefSubject and returned fallback Fx until recovery is replaced or routing stops.