[ric-oliv]

Part 2 of 6 for #5806, based on #5807. The Windows jobs spent much longer than Linux in setup, restore and the MSBuild job, for two reasons, one commit each.

Build the MSBuild job on all cores. msbuild.exe builds on one node unless it gets -m, while the dotnet CLI passes -maxcpucount on its own. The MSBuild job's binlog showed 21.4 minutes on a single node. -nr:false keeps the worker nodes from staying around after the build, since nothing later in the job uses them. In #5796 the job took 26.0 minutes against 29.6 to 30.3, with the same 44 warnings and 49 packages as a single-node build.

Install .NET and NuGet packages on a faster drive. The Windows images keep .NET under C:\Program Files\dotnet, where workloads install as MSI packages, and NuGet extracts packages into the user profile on C:.

• A new windows-dotnet-drive composite action puts .NET and the NuGet cache next to the workspace, where workloads install as plain files. On the x64 runners that's on D:.
• The arm64 runners only have C:, so there the NuGet packages and TEMP go on a Dev Drive. Trusting a freshly mounted Dev Drive can fail with "Access is denied" while the volume is still busy, so the action retries it. If setting up the drive fails anyway, the action warns and keeps the NuGet packages next to the workspace, so the job still runs, just slower.
• The build legs, the MSBuild job and verify-api's Windows job use it.

What #5782 and the probes #5798 and #5801 measured:

• On win-x64, Restore went from about 5 minutes to 1, and the workload step from 338 to 100 seconds.
• The MSBuild job's Run MSBuild step went from 23 to 24 minutes to 14.7, with only the drive.
• On win-arm64 the job took 33.8 and 32.4 minutes with NuGet and TEMP on the Dev Drive, against 37.2 and 35.8 without it. Putting .NET or the workspace on the Dev Drive too was slower. Turning off Defender's real-time scanning saved less, because the image already excludes C:\ and D:\.

On this PR's own CI

3 runs, including #5807, against main at b41b96c. The MSBuild job took 15.3, 14.4 and 14.8 minutes against 29.5, with Run MSBuild at 10.3 to 10.6 against 22.5. win-x64's Restore took 0.8 to 1.1 minutes against 6.0, and win-arm64's 2.2 to 2.8 against 4.0. win-arm64's Setup Environment stayed at 4.7 to 5.2. The whole stack's numbers are in #5806.

#skip-changelog

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.15%. Comparing base (881636f) to head (7fa3c1e).

Additional details and impacted files

@@                            Coverage Diff                            @@
##           ci/stop-installing-what-jobs-dont-use    #5808      +/-   ##
=========================================================================
+ Coverage                                  76.13%   76.15%   +0.02%     
=========================================================================
  Files                                        528      528              
  Lines                                      19579    19579              
  Branches                                    3829     3829              
=========================================================================
+ Hits                                       14906    14910       +4     
+ Misses                                      3791     3787       -4     
  Partials                                     882      882              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jamescrosswell]

About the only comment here is that we could put this in .github/actions/environment with if: runner.os == 'Windows'. This is where we've refactored all the setup logic rather than relying on each workflow remembering they need to do this as a separate step.