Summary
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When the same script file gets executed in multiple Runspaces, the RuntimeType generated from the powershell class defined in the file will be shared among those Runspaces. For different Runspaces, different SessionState should be used to run the static methods.
Fix
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We use the `SessionStateKeeper` to query for the correct `SessionState` to use for a static method call.
We already use `SessionStateKeeper` to track the `Runspace/SessionState` where a PowerShell class is defined, and thus we can leverage this for the static method invocation.
c5f3a19caf