Auto-derive BootstrapSdkVersion from global.json so it can never lag tools.dotnet

[Copilot]

eng/Versions.props::BootstrapSdkVersion and global.json::tools.dotnet were independently maintained, allowing them to drift. When they drift, the bootstrap shared runtime ends up older than what the SDK's tools require, producing host-resolution failures (You must install or update .NET to run this application).

Changes Made

• eng/Versions.props — Replace the hard-coded <BootstrapSdkVersion> with a reference to $(DotNetCliVersion), which is already read from global.json via regex in the same file. Drift is now structurally impossible.

  <!-- Before -->
  <BootstrapSdkVersion>10.0.106</BootstrapSdkVersion>
  
  <!-- After -->
  <!-- Derived from global.json so it can never lag tools.dotnet -->
  <BootstrapSdkVersion>$(DotNetCliVersion)</BootstrapSdkVersion>

• eng/cibuild_bootstrapped_msbuild.ps1 — Switch from parsing Versions.props as raw XML (which would read the unevaluated $(DotNetCliVersion) literal after the props change) to reading tools.dotnet directly from global.json via ConvertFrom-Json.

• eng/cibuild_bootstrapped_msbuild.sh — Same fix: read from global.json instead of grepping Versions.props. Uses jq when available for proper JSON path traversal (.tools.dotnet); falls back to grep/sed.

Both scripts now fail fast with a clear error if tools.dotnet cannot be read.

Testing

No new tests — the change is structural. The bootstrap CI pipelines (cibuild_bootstrapped_msbuild.ps1/.sh) exercise this path on every CI run.

Notes

The DotNetCliVersion regex pattern already existed in Versions.props for other purposes; BootstrapSdkVersion now piggybacks on it rather than duplicating logic or requiring a second independent update when Arcade bumps the SDK.

[dotnet-policy-service]

Hello @copilot, I noticed that you’re changing an .swr file or any file under src/Package/MSBuild.VSSetup.. Please make sure to validate this change by an experimental VS insertion. This is accomplished by pushing to an exp/* branch, which requires write permissions to this repo.

[ViktorHofer]

That's not a standard property. Use NetCoreSdkVersion instead: https://github.com/dotnet/sdk/blob/7bfcbfa069151ac1f7b602fd4cad874f99fb2c1d/src/Layout/redist/targets/GenerateBundledVersions.targets#L654

[ViktorHofer]

What we are missing here is doing some kind of Math.Min('$(NetCoreSdkVersion)', '10.0.106'))

[ViktorHofer]

This change seems wrong. It now always uses the SDK version from global.json. It would be better to still allow to hardcode a newer version via the BootstrapSdkVersion property but make sure that is never older than the SDK provided one.

I would use the msbuild -getproperty function here to avoid direct XML parsing and invoke some project that imports the microsoft.net.sdk, i.e. the msbuild.bootstrap.csproj.

This also applies to the bash changes.