# Fx.exhaustMap

Maps each element of an Fx to a new Fx, ignoring new elements until the current inner Fx completes.

## Signatures

```ts
export declare const exhaustMap: FlatMapLike;
```

## Why

`exhaustMap` is an admission policy for work that must never overlap and does
not need a backlog, such as ignoring repeated submit events while one submit
is running.

## Admission, ordering, and cardinality

The first source value observed while idle admits one inner Fx. For values
arriving while it runs, `f` is still evaluated to construct an inner, but that
inner is not run and no value is queued. Every admitted inner may emit any
number of values in its own order.

## Ownership and lifetime

Source and admitted-inner failures are forwarded and their services remain
typed. A `FiberHandle` in the required `Scope` owns the active inner. Source
completion waits for that inner; interruption closes the handle and the
inner's child Scope, running its finalizers.

## Examples

```ts
import { Fx } from "@typed/fx"
import { Effect } from "effect"

const submits = Fx.mergeAll(
  Fx.at("first", "0 millis"),
  Fx.at("ignored while busy", "5 millis"),
  Fx.at("later", "30 millis")
)
const accepted = Fx.exhaustMap(submits, (command) => Fx.at(command, "20 millis"))

Effect.runPromise(Effect.scoped(Fx.collectAll(accepted))).then(console.log)
// ["first", "later"]
```