GetOrderEndpoint.cs

public class GetOrderParams
{
    [FromRoute]
    public int OrderId { get; set; }

    [FromHeader(Name = "X-Tenant-Id")]
    public string TenantId { get; set; } = default!;

    [FromQuery]
    public bool IncludeLineItems { get; set; }
}

app.MapGet("/orders/{orderId}", ([AsParameters] GetOrderParams p, OrdersDb db) =>
{
    // p.OrderId    — from route
    // p.TenantId   — from request header
    // p.IncludeLineItems — from query string
});