The method `GetLookupDirectoryPaths` always returns the cached instance of path collection. However, the returned collection gets mutated in `CommandPathSearch.ResolveCurrentDirectoryInLookupPaths` to resolve the relative paths such as `.\tools` based on the user's current working directory `$PWD`, so for example, `.\tools` gets replaced with `cwd-1\tools` in the cached instance. Then, when the user changes to a different working directory `cwd-2`, command discovery won't find the executable or ps1 script under `cwd-2/tools` as expected, but those executables under `cwd-1\tools` will always be discoverable no matter what the `$PWD` is. That behavior is incorrect.
This pull request improves the caching logic of `GetLookupDirectoryPaths` and makes it return a copy of the path collection, so the mutation happens to the returned copy, and the cached instance is kept intact. So, for every command search, the `CommandPathSearch` will resolve relative paths against the `$PWD` that the user is located at that time.
Dongbo Wang