Summary

Expand test coverage for Core/RateLimitingService.cs edge cases (empty identifier, boundary at limit, window reset behavior).

Where to look

• Core/RateLimitingService.cs
• Tests/Unit/Core/ (add or extend tests following existing patterns)

Acceptance criteria

• New tests in Tests/HelloblueGK.Tests.csproj
• dotnet test Tests/HelloblueGK.Tests.csproj passes
• Tests are deterministic (no timing flakes)