tests-xunitlisted

# Backend tests: xUnit (.NET) Write and run backend tests using xUnit conventions and the repository's backend test command from crew config (e.g. `dotnet test`). Integration tests exercise the .NET layer end to end where the project has them. ## Running If your dispatch hands you an artifacts path, add `--artifacts-path <path>` to every `dotnet test` run: the build and lint gates may be running beside you on their own paths (`backend-dotnet`, "Parallel gates"). - **Targeted rerun:** `--filter`. Every filter is `<property><op><value>`, so the property is never left off: `dotnet test --filter "FullyQualifiedName~Namespace.ClassName"` for a class, `--filter "FullyQualifiedName~Namespace.ClassName.MethodName"` for one test. - **Discovery:** `dotnet test --list-tests --filter "FullyQualifiedName~Namespace.ClassName"` prints the tests the runner sees in that class. When it lists nothing, rerun `--list-tests` without the filter: if the rest of the project's tests appear, the value is misspelled or the namespace differs from the folder. When the unfiltered list is empty too, the cause is in the project file: the test project is missing `Microsoft.NET.Test.Sdk` or `xunit.runner.visualstudio`, is not in the solution, or has a stale build. Read the `.csproj`/`.sln`; never run `strings`, `ildasm` or the like over `bin/`. - **Summary line:** `Total tests: 0` is the zero-tests failure. - **Skip mechanism:** `Skip = "…"` on the attribute.