timeout on send

[plastikfan]

consider using an output controller, that was created before but not required then:

type outputController struct {
	pool *core.TraversePool
	wg   pants.WaitGroup
}

func (c *outputController) Conclude(ctx context.Context) {
	c.pool.Conclude(ctx)
}

func (c *outputController) StartCancellationMonitor(ctx context.Context,
	cancellation *core.Cancellation,
) {
	if cc := c.pool.CancelCh(); cc != nil {
		pants.StartCancellationMonitor(ctx,
			cancellation.Cancel,
			c.wg,
			cc,
			cancellation.On,
		)
	}
}

core:

	// OutputFunc
	OutputFunc func(ctrl OutputController, outs OutputStream)