# Fx.mapError

Transforms typed failures while preserving defects and interruption.

## Signatures

```ts
export declare const mapError: {
    <E, E2>(f: (e: E) => E2): <A, R>(self: Fx<A, E, R>) => Fx<A, E2, R>;
    <A, E, R, E2>(self: Fx<A, E, R>, f: (e: E) => E2): Fx<A, E2, R>;
};
```

## Why

Libraries can expose a domain error without losing the richer Cause that
Effect uses for defects, interruption, and composed failures.

## Ownership and lifetime

The mapping function runs synchronously for each `Cause.Fail` reported by
the source. It does not run for defects or interrupts, which pass through
unchanged. Values retain order and cardinality. No resource is acquired and
the returned Fx has the same subscription lifetime and services as its source.

## Examples

```ts
import { mapError } from "@typed/fx/Fx"
import { fail } from "@typed/fx/Fx"

const domainFailure = mapError(fail(404), (status) => ({ _tag: "HttpError", status }))
```