Curly Bracketn't Todos List API in C#

ConsoleApp1.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
	<LangVersion>preview</LangVersion>
	<Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Http" Version="2.2.2" />
    <PackageReference Include="Microsoft.AspNetCore.Routing" Version="2.2.2" />
  </ItemGroup>

</Project>

Program.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.Hosting;
using System;
using System.Linq;
using System.Threading.Tasks;
using System.Text.Json;
using System.Collections.Concurrent;
using System.Collections.Generic;
using Microsoft.Extensions.DependencyInjection;

int id = 1;
ConcurrentDictionary<int, TodoItem> items = new();

await Host.CreateDefaultBuilder(args)
    .ConfigureServices(services => services.AddRouting())
    .ConfigureWebHost(webBuilder => webBuilder
        .Configure(app => app
            .UseRouting()
            .UseDeveloperExceptionPage()
            .UseEndpoints(SetupRoutes))
        .UseKestrel())
    .Build()
    .RunAsync();

IEndpointRouteBuilder Map(
    IEndpointRouteBuilder builder,
    HttpMethodRouter action, 
    params (string path, RequestDelegate handler)[] gets) =>
    gets.Select(route => action(route.path, route.handler))
        .Select(_ => builder).ToList().Last();

void SetupRoutes(IEndpointRouteBuilder route) =>
    Map(Map(Map(Map(route, 
        route.MapGet,
       ("/api/todos/", GetTodoItems),
       ("/api/todos/{id}", GetTodoItem)),
        route.MapPost,
       ("/api/todos/", AddTodoItem)),
        route.MapPut,
       ("/api/todos/", UpdateTodoItem)),
        route.MapDelete,
       ("/api/todos/{id}", DeleteTodoItem));

Task GetTodoItems(HttpContext context) =>
    context.Response.WriteAsync(JsonSerializer.Serialize(items.Values.ToArray()));

Task GetTodoItem(HttpContext context) =>
    context.Response.WriteAsync(JsonSerializer.Serialize(FetchByid(GetPathId(context))));

async Task AddTodoItem(HttpContext context) =>
    Pass(Pass(
        await ReadCreateTodoItem(context.Request),
        item => items.TryAdd(item.id, item)),
        item => context.Response.WriteAsync(JsonSerializer.Serialize(item)));

async Task UpdateTodoItem(HttpContext context) =>
    Pass(Pass(
        await ReadTodoItem(context.Request),
        item => items[item.id] = item),
        item => context.Response.WriteAsync(JsonSerializer.Serialize(item)));

Task DeleteTodoItem(HttpContext context) =>
    Pass(Task.CompletedTask, task => items.TryRemove(GetPathId(context), out TodoItem? value));

static async Task<TodoItem> ReadTodoItem(HttpRequest request) => 
    JsonSerializer.Deserialize<TodoItem>(new ReadOnlySpan<byte>(
        await PassAsync(new byte[(int)request.ContentLength!], 
        async bytes => await request.Body.ReadAsync(bytes))))!;

async Task<TodoItem> ReadCreateTodoItem(HttpRequest request) =>
    Pipe(JsonSerializer.Deserialize<CreateTodoItem>(new ReadOnlySpan<byte>(
        await PassAsync(new byte[(int)request.ContentLength!], 
        async bytes => await request.Body.ReadAsync(bytes))))!,
        create => new TodoItem(create.title, id: id++));

static int GetPathId(HttpContext context) => int.Parse((string)context.GetRouteValue("id"));

TodoItem FetchByid(int id) => 
    items.TryGetValue(id, out TodoItem? item) ? item! : throw new KeyNotFoundException();

static T Pass<T, U>(T something, Func<T, U> consume) => 
    consume(something) is U ? something : something;

static async Task<T> PassAsync<T, U>(T something, Func<T, Task<U>> consume) => 
    await consume(something) is U ? something : something;

static U Pipe<T, U>(T something, Func<T, U> transform) => transform(something);

delegate IEndpointConventionBuilder HttpMethodRouter(string path, RequestDelegate handler);

public record CreateTodoItem(string title);

public record TodoItem(string title, int id, bool isCompleted = false);