Issue: MaxLength Validation Bypassed with JsonIgnore(WhenWritingDefault)

Summary

When using ASP.NET Core's AddValidation() in .NET 10, the [MaxLength] validation attribute is bypassed on properties that also have [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)].

Expected Behavior

Validation should work regardless of JsonIgnore attributes, since JsonIgnoreCondition.WhenWritingDefault only affects serialization output, not deserialization or validation.

Actual Behavior

Properties with [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)] skip validation entirely, allowing invalid data through.

Reproduction

public class ValidationTestRequest
{
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    [MaxLength(10)]
    public string? PropertyWithJsonIgnoreWhenWritingDefault { get; set; }

    [MaxLength(10)]
    public string? PropertyWithoutJsonIgnore { get; set; }
}

var builder = WebApplication.CreateBuilder();
builder.Services.AddValidation();

var app = builder.Build();
app.MapPost("/test-validation", (ValidationTestRequest _) => Results.Ok());

• POST with { "PropertyWithoutJsonIgnore": "ExceedsMaxLength" } returns 400 Bad Request (correct)
• POST with { "PropertyWithJsonIgnoreWhenWritingDefault": "ExceedsMaxLength" } returns 200 OK (incorrect)

Running the Tests

dotnet test

Expected output:

• MaxLengthValidation_ReturnsBadRequest_WhenValueExceedsLimit - Pass
• MaxLengthValidation_ReturnsBadRequest_WhenPropertyHasJsonIgnoreWhenWritingDefault - Fail

Environment

• .NET 10
• Microsoft.AspNetCore.TestHost 10.0.0
• MSTest 4.0.1