Add paired-repository CI and pin the formatter toolchain

[dv00d00]

Problem

The tracked Directory.Build.targets makes local sibling checkouts reproducible enough to build, but the repository has no GitHub Actions workflow. Pull requests therefore do not prove that they use the intended AngleSharp source revision, build the complete solution, preserve formatting, or pass the supported test matrix.

CSharpier configuration is checked in, but its version is not pinned by a local .NET tool manifest. global.json selects the test runner but does not select an SDK feature band.

Direction

Add a focused paired-repository CI workflow before NuGet publishing work in #9:

1. Check out AngleSharp.ReadOnlyDom and the compatible dv00d00/AngleSharp revision into the sibling layout expected by the tracked targets file.
2. Set AngleSharpSourceRoot explicitly and verify that the source AngleSharp.Core.csproj is selected instead of the NuGet package.
3. Restore once, build the solution serially (-m:1) because both solutions share AngleSharp output paths, and keep warnings at zero.
4. Run a fast pull-request gate plus the complete net10.0 suite on merge/schedule if the full corpus is too slow for every push.
5. Add .config/dotnet-tools.json pinning CSharpier and document dotnet tool restore plus the exact check command.
6. Select the .NET 10 SDK feature band explicitly while allowing an intentional servicing roll-forward policy.

Acceptance criteria

• A clean GitHub-hosted checkout restores and builds the complete Release solution against the intended AngleSharp source commit.
• CI fails if the package reference is used accidentally or the paired source revision is incompatible.
• Pull requests receive a bounded-time correctness gate with zero warnings.
• The complete net10.0 suite runs on an explicit merge/scheduled gate and uploads its test report on failure.
• CSharpier is restored from a repository-local manifest and checked without relying on a global tool installation.
• The SDK setup and roll-forward policy are documented and reproducible on developer machines.
• Forked pull requests require no write-capable secrets.

[dv00d00]

2026-08-20 triage: keep open and treat as the highest-priority repository task. PR #96 demonstrated the current gap: the net11.0 preview sample built and passed local review, but GitHub reported no checks. The workflow now needs a .NET 10 library/test lane plus the explicit .NET 11 preview sample build, while retaining the paired AngleSharp source checkout and formatter pinning already described here.

[dv00d00]

Parking this infrastructure epic. CI should be designed only after the repository/package boundary and supported SDK matrix are chosen; until then review and verification remain manual. Reopen when there is a concrete publication or handover target that defines the paired checkout, release SDKs, and required gates.

[dv00d00]

Reopening for completion. The paired build/test workflow now exists; the remaining work is to pin the paired AngleSharp revision and formatter toolchain, enforce formatting in CI, make the SDK policy reproducible, add the explicit .NET 11 preview sample lane, and retain complete test/report coverage for handover.

[dv00d00]

Completed in #102.

• Paired AngleSharp is pinned to 4819b43afb663ba29d37eb4f09abd072fed1966e and verified as a source ProjectReference.
• The hard-coded sibling project was removed from the solution, making AngleSharpSourceRoot authoritative.
• .NET 10 is pinned to the 10.0.3xx feature band with servicing-only roll-forward.
• CSharpier 1.3.0 is pinned in the local tool manifest; the repository is fully formatted and CI enforces it.
• Full net10 tests require at least 179,000 discovered cases and emit a TRX report, uploaded on failure.
• Pull requests, main pushes, and the weekly schedule run the gates without write-capable secrets.
• The .NET 11 preview runtime-async Hacker News/Streaming lane is active.

PR CI and the post-merge main run are green: https://github.com/dv00d00/AngleSharp.ReadOnlyDom/actions/runs/32424350247