PR Summary

Fix Start-Process to handle Windows shell: URIs by detecting the shell: prefix and bypassing CommandDiscovery lookup. Instead pass the URI directly to ShellExecute.

Fixes #25397

PR Context

Problem

On Windows, Start-Process fails when given shell: URIs with a \ like shell:::{8E908FC9-BECC-40f6-915B-F4CA0E70D03D}\Advanced. The root cause is in CommandSearcher.CanDoPathLookup(). When the command contains a backslash, it returns DirectorySeparator, which triggers a code path in setupPathSearcher() that calls ResolvePSPath() → GetNextLiteralPathThatExists() → LocationGlobber.GetProviderPath(). This parses the shell: prefix as a PowerShell provider name and throws ProviderNotFoundException. Without the backslash (shell:::{GUID}), the command takes a different code path and works.

Solution

Add a check in StartProcessCommand.BeginProcessing() to detect shell: URIs on Windows and skip the CommandDiscovery lookup. Instead pass the URI directly to ShellExecute. Cmldet Working Group recommends this solution.

Add test case in "Bug fixes" block to verify shell: URIs don't throw ProviderNotFoundException.

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