How does exception handling middleware interact with model validation errors in ASP.NET Core, and how do they typically produce different error response paths?

Model validation errors (from [ApiController]'s automatic model state validation, or FluentValidation-style validators) typically don't throw exceptions at all -- instead, [ApiController] automatically short-circuits with a 400 Bad Request and a ValidationProblemDetails response before the action method even executes, entirely bypassing exception-handling middleware since no exception was ever thrown; this is a distinct, separate error path from actual unhandled exceptions, which is why validation errors and unhandled exceptions often need separate consideration when designing a consistent overall error response strategy.

[ApiController]  // enables automatic model validation short-circuiting
public class ProductsController : ControllerBase {
    [HttpPost]
    public IActionResult Create([Required] ProductDto dto) {
        // If dto fails validation, this method body never executes --
        // [ApiController] already returned a 400 ValidationProblemDetails automatically
        return Ok();
    }
}