Summary of the new feature / enhancement

When running a PowerShell script in a new Runspace, I want to set the working directory. Currently, I cannot set it using InitialSessionState, and instead have to first .Open() the Runspace and then set it by calling runspace.SessionStateProxy.Path.SetLocation(...);.

This is

1. cumbersome – almost everything else can be set declaratively using initialSessionState, but not the working directory, even through the working directory setup is handled there (in .Bind and .SetSessionStateDrive),
2. wrong – any modules imported during .Open() (configured using initialSessionState.ImportPSModules(...)) will see the process-wide .NET working directory, especially script modules with top-level statements.

To avoid issue 2., I believe this ugly hack is currently required (which could have side-effects for other running threads):

var originalWorkingDirectory = Environment.CurrentDirectory;
try {
    Environment.CurrentDirectory = ...;
    runspace.Open();
} finally {
    Environment.CurrentDirectory = originalWorkingDirectory;
}

Proposed technical implementation details (optional)

Add an initialSessionState.WorkingDirectory string property, initially set to null, which can be overwritten with a custom working directory. If unchanged, the current behavior is kept, so it should be a backwards compatible change. If the directory does not exist, throw an exception.

If we agree on this solution, I could try implementing a PR.