Explain the ASP.NET Core hosting model (Host Builder + Kestrel + Startup flow).

ASP.NET Core uses a unified Host (Generic Host / Web Host) that wires together configuration, logging, dependency injection, environment, and the HTTP pipeline.

• The host sets up configuration (appsettings, environment variables, command line, etc.).
• It constructs the DI container and registers application services.
• It configures and starts Kestrel as the web server.
• It builds the middleware pipeline and endpoint routing (MVC, Razor Pages, minimal APIs).

The high-level flow is: Host ? Kestrel ? Middleware pipeline ? MVC / Razor ? View or JSON result. This gives full low-level control over startup and behavior.