# mapError

Transforms the output (Fx) error channel of a `Push` using the provided function.

Failures (Cause) are mapped via `Cause.map`, so only the typed failure (`Fail`)
is transformed; defects and interrupts are preserved unchanged.

Mirrors `Effect.mapError` on the Fx side. Cardinality, value order, input
callbacks, and output service requirements are unchanged.

## Signatures

```ts
export declare const mapError: {
    <E2, E3>(f: (e: E2) => E3): <A, E, R, B, R2>(push: Push<A, E, R, B, E2, R2>) => Push<A, E, R, B, E3, R2>;
    <A, E, R, B, E2, R2, E3>(push: Push<A, E, R, B, E2, R2>, f: (e: E2) => E3): Push<A, E, R, B, E3, R2>;
};
```

## Why

Normalize an output failure type at the observation boundary without touching
input errors or collapsing defects and interruption into typed failures.

## Ownership and lifetime

The mapping is synchronous and resource-free. It runs when the output Cause is
delivered and preserves the upstream subscription, Scope, interruption, and
cleanup behavior.

## Examples

```ts
import { Effect } from "effect"
import * as Fx from "@typed/fx/Fx"
import * as Push from "@typed/fx/Push"
import * as Sink from "@typed/fx/Sink"

const push = Push.make(Sink.make(() => Effect.void, (_: string) => Effect.void), Fx.fail("offline"))
const normalized = Push.mapError(push, (message) => ({ message }))
```