# Fx.Emit

Operations supplied to a callback producer for emitting values or ending its run.

## Signatures

```ts
export type Emit<A, E = never> = {
    succeed: (value: A) => Fiber<unknown, never>;
    failCause: (cause: Cause.Cause<E>) => Fiber<unknown, never>;
    fail: (error: E) => Fiber<unknown, never>;
    die: (error: unknown) => Fiber<unknown, never>;
    done: () => Fiber<unknown, never>;
};
```

## Why

Callback sources need an explicit bridge into Sink operations while retaining the
distinction between typed failures, defects, interruption causes, and completion.

## Ownership and lifetime

An `Emit` is valid only for the active callback run. Every operation forks the
corresponding sink Effect in that run's scope and returns its `Fiber`; callers may
inspect or interrupt that delivery. Retaining it after cleanup is unsupported.

## Property: die

Starts delivery of one unexpected defect and returns the delivery fiber.

## Property: die: Why

Programming defects remain outside the typed `E` channel.

## Property: die: Ownership and lifetime

The active callback scope owns the returned fiber. The value is wrapped with
`Cause.die` and forwarded to the sink.

## Property: done

Requests early completion and returns the sink's early-exit fiber.

## Property: done: Why

Finite callback APIs need an explicit completion signal distinct from failure.

## Property: done: Ownership and lifetime

The active callback scope owns the returned fiber. Early exit ends the run and
causes callback cleanup registered by `callback` to execute.

## Property: fail

Starts delivery of one typed failure and returns the delivery fiber.

## Property: fail: Why

Expected callback errors enter `E` without being converted to defects.

## Property: fail: Ownership and lifetime

The active callback scope owns the returned fiber. The error is wrapped with
`Cause.fail` and forwarded to the sink.

## Property: failCause

Starts delivery of a complete Effect `Cause` and returns the delivery fiber.

## Property: failCause: Why

Typed failures, defects, and interruption remain structurally distinct.

## Property: failCause: Ownership and lifetime

The active callback scope owns the returned fiber. This operation does not
automatically call `done`; terminal behavior is determined by the sink.

## Property: succeed

Starts delivery of one value and returns the delivery fiber.

## Property: succeed: Why

Callback producers push values when they arrive instead of waiting to be pulled.

## Property: succeed: Ownership and lifetime

The active callback scope owns the returned fiber; deliveries can overlap when
`succeed` is called again before an earlier sink Effect completes.