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# `workflows/concurrent`

Source: [`src/workflows/concurrent.ts`](https://github.com/AI-for-dev/combo/blob/main/src/workflows/concurrent.ts)

Running several things at once, but not all of them: a subtask is a session,
and N sessions opening together is the bill nobody meant to pay.

## `mapConcurrent`

*function*

```typescript
export async function mapConcurrent<T, R>(
	items: readonly T[],
	concurrency: number,
	run: (item: T, index: number) => Promise<R>,
): Promise<R[]> { /* … */ }
```

Runs `run` over `items` with at most `concurrency` in flight, in index order.

A bounded worker pool, not a `Promise.all`: N subtasks must not open N
sessions at once. Results come back **in the order of `items`**, whatever the
order they finished in - a caller reading `results[2]` means the third task,
always.

`run` is expected to handle its own failures; a rejection here rejects the
whole map, which is why every combinator hands it a function that returns a
failed `Result` instead of throwing.