Exclude NuGet cache from project file search in ProjectLocator

[MO2k4]

Summary

• Fixes aspire update incorrectly surfacing immutable NuGet template packages (e.g. aspire.projecttemplates) as updatable AppHost projects when run from a broad directory like ~
• Replaces Directory.GetFiles with FileSystemEnumerable using ShouldRecursePredicate to skip the NuGet cache directory before descending into it
• Resolves the cache path from NUGET_PACKAGES env var or the platform-appropriate default (~/.nuget/packages)

Fixes #14055

Test plan

• Added test: FindAppHostProjectFilesAsync_ExcludesProjectsInsideNuGetCache — verifies projects inside the NuGet cache are excluded
• Added test: FindAppHostProjectFilesAsync_FindsProjectsOutsideNuGetCache — verifies normal project discovery still works
• Added test: FindAppHostProjectFilesAsync_RespectsCustomNuGetPackagesEnvVar — verifies custom NUGET_PACKAGES paths are honored

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 15388

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 15388"

[davidfowl]

Tests shouldn't set env variables like this, it affects the ability to run concurrently and can impact other tests.

[MO2k4]

Thanks for the feedback, i've adjusted this and now switched to CliExecutionContext

[mitchdenny]

Good fix for a real user-facing issue — the FileSystemEnumerable approach with ShouldRecursePredicate is the right call for skipping the NuGet cache early instead of filtering after the fact.

One bug to address: the StartsWith check in ShouldRecursePredicate lacks a trailing directory separator, which means it could false-positive on sibling directories whose names share a prefix with the cache path (e.g., .nuget/packages-extra). See inline comment for the suggested fix.

Tests are well-structured and cover the key scenarios.

[mitchdenny]

Bug: StartsWith without a trailing directory separator can produce false positives. For example, if the NuGet cache path is /home/user/.nuget/packages, a sibling directory named /home/user/.nuget/packages-extra would also be incorrectly excluded because "/home/user/.nuget/packages-extra".StartsWith("/home/user/.nuget/packages") is true.

The codebase already handles this correctly in BundleService.cs (zip-slip protection) by appending Path.DirectorySeparatorChar before comparing. Suggested fix:

ShouldRecursePredicate = (ref FileSystemEntry entry) =>
{
    if (nugetCachePath is null)
    {
        return true;
    }
    var dirPath = entry.ToFullPath();
    return !dirPath.Equals(nugetCachePath, pathComparison)
        && !dirPath.StartsWith(nugetCachePath + Path.DirectorySeparatorChar, pathComparison);
}

The extra Equals check handles the exact cache root directory itself (since the StartsWith with trailing separator won't match it).