The dotnet-hosted Roslyn 2.10 build cannot start its VBCSCompiler server
under a current dotnet host, so with /shared every test compilation first
waited out the client's full 20-second new-server connection timeout
before falling back to a sub-second in-process compile. Since the 2.10
configurations were enabled on non-Windows (#3914), that added ~29
minutes to the Linux CI job and ~43 minutes on macOS: ~340 affected
tests at ~21s each, versus ~0.2s for the toolsets whose server works.
Assisted-by: Claude:claude-fable-5:Claude Code
Siegfried Pammer