# onExit

Observes the Fx's final success or failure with an Effect finalizer.

## Signatures

```ts
export declare const onExit: {
    <A, E, XE = never, XR = never>(f: (exit: Exit.Exit<void, E>) => void | Effect.Effect<void, XE, XR>): <R>(self: Fx<A, E, R>) => Fx<A, E | XE, R | XR>;
    <A, E, R, XE = never, XR = never>(self: Fx<A, E, R>, f: (exit: Exit.Exit<void, E>) => void | Effect.Effect<void, XE, XR>): Fx<A, E | XE, R | XR>;
};
```

## Why

Teardown and audit work sometimes depends on how the complete subscription
ended. An `Exit` preserves that distinction without materializing it as a
stream value.

## Ownership and lifetime

The finalizer runs once after successful completion, a reported source cause,
or interruption of the running fiber. The success Exit carries `void`
because an Fx may emit many values and has no single terminal success value.
A finalizer failure after normal completion is reported in the returned error
channel. After a source failure or interruption it is suppressed so the
already-observed termination remains authoritative. Finalizer services live
for the subscription only.

## Examples

```ts
import { Effect, Exit } from "effect"
import { onExit } from "@typed/fx/Fx"
import { succeed } from "@typed/fx/Fx"

const audited = onExit(succeed("ready"), (exit) =>
  Effect.log(Exit.isSuccess(exit) ? "complete" : "failed")
)
```