fix(build): restore the tools once per build instead of once per project

[xperiandri]

Proposed Changes

ToolRestore runs in every project before its restore, and a solution restores its projects in parallel, so several projects can run dotnet tool restore at the same time and touch the same marker file. Every project now delegates to one instance of Directory.Build.targets, which MSBuild builds once per build, so the tools are restored once and the projects that ask at the same time wait for that run. The Restore dependencies step of the Copilot setup no longer runs dotnet tool restore on its own before restoring the solution. Format gets a comment that says why it runs Fantomas twice.

Types of changes

What types of changes does your code introduce to FSharp.Control.R3?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• Build and tests pass locally – build.cmd with CI=true and ENABLE_COVERAGE=true; a solution restore without the marker file restores the tools once, and a repeated one does not restore them
• I have added tests that prove my fix is effective or that my feature works (if appropriate) – only the build infrastructure changes
• I have added necessary documentation (if appropriate) – the reasons are in the comments of Directory.Build.targets

Further comments

No failure was observed in this repository: in five local solution restores without the marker file the tools were restored once each time, before and after the change. Whether the projects overlap depends on timing, so the change removes the possibility rather than a reproduced failure.

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The MSBuild delegation correctly serializes identical restoration requests without changing normal restore behavior.

0 open findings

What changed in this PR

This PR prevents concurrent local-tool restores by coordinating them through a single MSBuild project instance.

Changes:

• Delegates tool restoration to the incremental ToolRestoreOnce target.
• Removes redundant tool restoration from Copilot setup.
• Documents the intentional second Fantomas pass.

File	Description
Directory.Build.targets	Coordinates tool restoration and documents formatting behavior.
.github/​workflows/​copilot-setup-steps.yml	Relies on solution restore to restore local tools.

🧠 Review effort: Balanced

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