The sandbox is a restricted area in which Claude Code runs commands, allowed to reach only certain folders. On Windows, Claude Code now looks for the NuGet packages folder at ~/.nuget/packages when it starts. NuGet is the package manager used by .NET and dotnet builds.
It skips this check when:
NUGET_PACKAGESor a similar variable is set, since that already points to a different folder.- The path contains characters such as
',;or%.
If the folder, or the folder above it, is among the places the sandbox may read, Claude Code passes its location on so sandboxed commands can use it. If the check fails, Claude Code logs a warning that it could not find out whether sandboxed commands can read your NuGet packages folder, and that a sandboxed dotnet build may not find restored packages.
This helps dotnet builds run inside the Windows sandbox find packages that were already downloaded. If you see the warning, a sandboxed build may fail to find them.