IUniTaskAsyncEnumerableを使って操作の先行入力を実現する

public class Sandbox1 : MonoBehaviour
{
    public void Start()
    {
        var channel = Channel.CreateSingleConsumerUnbounded<ICommand>();
        SetupWriter(channel.Writer);
        SetupReader(channel.Reader).Forget();
    }

    private void SetupWriter(ChannelWriter<ICommand> channelWriter)
    {
        Observable
            .EveryUpdate()
            .Where(_ => Input.GetKeyDown(KeyCode.A))
            .Subscribe(_ =>
            {
                Debug.Log($"Write CommandA {Time.time:0.00}");
                channelWriter.TryWrite(new CommandA { Time = Time.time });
            })
            .AddTo(this);

        Observable
            .EveryUpdate()
            .Where(_ => Input.GetKeyDown(KeyCode.B))
            .Subscribe(_ =>
            {
                Debug.Log($"Write CommandB {Time.time:0.00}");
                channelWriter.TryWrite(new CommandB { Time = Time.time });
            })
            .AddTo(this);
    }

    private async UniTask SetupReader(ChannelReader<ICommand> channelReader)
    {
        await foreach (var command in channelReader.ReadAllAsync(this.GetCancellationTokenOnDestroy()))
        {
            Debug.Log($"アニメ開始 {command} {command.Time:0.00}");
            await UniTask.Delay(TimeSpan.FromSeconds(1));
            Debug.Log($"アニメ修了 {command} {command.Time:0.00}");
        }
    }
}

public interface ICommand
{
    float Time { get; }
}

public class CommandA : ICommand
{
    public float Time { get; set; }
}

public class CommandB : ICommand
{
    public float Time { get; set; }
}