PR Summary

Fix #26536

There are 2 issues surfaced from #26536 that we need to address:

1. The error reporting in the method ReportExceptionFallback(Exception e, string header) does not write out stack trace of the exception, which makes it hard to diagnose failures like ShellCannotBeStarted.
2. The UpdatePath method used in module path construction doesn't handle the case where personalModulePathToUse may contain multiple paths separated by the PathSperator (user can define PSModulePath in powershell.config.json with such a value).

The fixes are:

1. Write out stack trace of the exception in ReportExceptionFallback(Exception e, string header), at the end.
2. Refactored the module path construction code to make it more robust and easier to maintain
   • Removed the old existing UpdatePath method.
   • Removed the old PathContainsSubstring method. Change to a difference approach that is much more efficient.
   • Refactored the AddPath method and rename it to be UpdatePath
   • Updated SetModulePath() to not blindly add a path separator when the environment variable PSModulePath is initially not set in all scopes.
   • Call SetModulePath() in the static constructor of ModuleIntrinsics instead of the instance constructor. So, we only need to construct the module path once per process (instead of once per a new Runspace).

With the changes, PowerShell won't crash even if the personal module path is like C:\Users\marcv\OneDrive - company & name namepart2\Dokumente\PowerShell\Modules as reported in the issue.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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• Breaking changes
  • None
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  • Experimental feature(s) needed
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• User-facing changes
  • Not Applicable
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  • Documentation needed
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• Testing - New and feature
  • N/A or can only be tested interactively
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  • Make sure you've added a new test if existing tests do not effectively test the code changed