Publish to AWS wizard fails at App Runner name validation step with generic "error occurred in deployment tool" message

Environment

Visual Studio version: [check Help → About Microsoft Visual Studio]
AWS Toolkit for Visual Studio version: [check Extensions → Manage Extensions → Installed]
Target: ASP.NET Core 8 Web API, deploying via "Publish to AWS" → App Runner
OS: Windows 11

Steps to reproduce

Right-click ASP.NET Core 8 Web API project → Publish to AWS
Select AWS App Runner as deployment target
Enter application name real-estate-ai
Field shows red outline validation error
Popup appears: "An error occurred in the deployment tool. If this problem persists, please report an issue on GitHub."

Start by reproducing the failure through an ASP.NET Core 8 Web API project using Publish to AWS → App Runner, with application name real-estate-ai, on Windows 11. Inspect the App Runner name-validation flow and the deployment-tool error handling. Done means valid input no longer produces the generic error, while invalid input reports a useful validation result.

Written by the indexing model from the issue text.