feat(dotnet): add core reporter (listener, collector, writer, SPI hook)

[edblackburn]

Summary

Adds the .NET reporter core: an MTP V2 (Microsoft Testing Platform) in-process extension that captures test results and writes .claude/tdd-guard/data/test.json. Framework-agnostic — any MTP V2-hosted framework works without reporter changes.

Scope

Following your guidance on issue #84 ("keeping the PR focused and the initial implementation simple will make it much easier for me to review") and the shape you accepted for the JUnit5 reporter (#160 — listener, collector, JSON writer, SPI/hook registration, build wrapper, unit tests only), this PR is scoped identically:

• TddGuard.Dotnet.Core/ — pure domain types and functions, no MTP dependency
• TddGuard.Dotnet/ — the MTP V2 extension (listener + builder hook)
• TddGuard.Dotnet.Tests/ — unit and property-based tests only

No src/ changes. No CI changes (separate PR, stacked on this one). No integration test factory or framework compatibility smoke tests (separate PRs, same as JUnit5's follow-up sequence).

Design

• Domain logic (Core) has zero MTP dependency — testable without a test host
• Errors are values: ProjectRootResolver.Resolve() returns OneOf<ProjectRoot, ResolveError>, no exceptions for flow control
• Per ADR-010: when neither TDD_GUARD_PROJECT_ROOT nor CLAUDE_PROJECT_DIR is set, the extension disables itself and logs to stderr — it does not silently fall back to cwd
• Cross-platform path handling: Path.GetFullPath() + normalized comparison for the ancestor-of-cwd check (handles Windows separators, case-insensitivity, trailing separators, macOS /var → /private/var symlinks)

Testing

70 unit tests, including property-based roundtrip serialization (FsCheck). All pass on .NET 10.

Distribution

Planned for NuGet.org, published by you — following up separately on issue #84.

Stacked PRs

This is the first of a stack of 4 PRs decomposing the reporter the way JUnit5 landed:

1. This PR — core reporter
2. feat/dotnet-ci → CI build step
3. feat/dotnet-integration-tests → Node integration test factory + minimal fixtures
4. feat/dotnet-framework-compat → framework compatibility smoke tests

Each is based on the previous, so they'll show as small incremental diffs once opened.

[nizos]

Hi @edblackburn,

Thanks for the PR! I'm back from vacation and should be able to look at it this weekend. Talk to you soon! :)

[nizos]

Hi @edblackburn,

Thanks for the PR and great work! I closed and re-opened the PR just to get the npm audit check to pick up a dependency fix that landed on main earlier today.

I will merge this and follow up with dotnet support in the devcontainer.

A few things that I would like your read on before we publish:

• Timed out and cancelled tests currently serialize as passed. They land in the _ => Passed() catch-all in ConsumeAsync. Should we map both to failed with a message? Fail closed feels right for TDD Guard. Could the FsCheck generator grow to cover those states too?
• Should we pin the floating package versions (OneOf 3.*, TUnit 0.*, FsCheck 3.*)?
• On packaging shape, TddGuard.Dotnet.Core is packable and referenced by the main project, so packing produces a second package that also needs publishing, unless I missed something. I would prefer to publish a single TddGuard.Dotnet package. How would you approach that?
• There is no solution file today, so the README's dotnet build from reporters/dotnet fails with MSB1003. Should we add one or update the command? Currently dotnet run --project TddGuard.Dotnet.Tests works for me.
• Can we take a look at HandlesConcurrentConsumeAsyncCallsSafely? It blocks 100 thread pool threads on a Barrier and takes most of the suite time on my machine. I suspect small CI runners will feel it even more.
• Two small notes: TddGuardListener.Version says 1.0.0 while the packages are 0.1.0, and .globalconfig mentions TestResultsWriter that I think is now ReportFileWriter.

Thanks again, this is outstanding work. I have now been looking forward to it and I'm glad to have you as a contributor. Excited for the rest of the stack so we can get it published. :)