lightweight variant

CursorLang.Core/Interop/PackageIdentityNative.cs

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+using System.Runtime.InteropServices;
+
+namespace CursorLang.Core.Interop;
+
+/// <summary>
+/// Answers whether the application runs from an MSIX package.
+/// </summary>
+/// <remarks>
+/// The same application runs both installed from the Store and simply unpacked
+/// into a folder. Some Windows features — startup through <c>StartupTask</c>, for
+/// instance — are available only to a package, and reaching for them without a
+/// check is not allowed: outside a package they throw.
+/// </remarks>
+internal static class PackageIdentityNative
+{
+    /// <summary>APPMODEL_ERROR_NO_PACKAGE — the process runs outside a package.</summary>
+    private const int NoPackage = 15700;
+
+    /// <summary>
+    /// The application runs from an MSIX package.
+    /// </summary>
+    /// <remarks>
+    /// The value is computed once: it cannot change during the lifetime of
+    /// the process.
+    /// </remarks>
+    internal static bool IsPackaged { get; } = DetectPackage();
+
+    private static bool DetectPackage()
+    {
+        // The answer comes from the return code rather than from the name itself, so
+        // no buffer is needed: with zero length a package replies complaining about space
+        uint length = 0;
+        return GetCurrentPackageFullName(ref length, IntPtr.Zero) != NoPackage;
+    }
+
+    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
+    private static extern int GetCurrentPackageFullName(ref uint packageFullNameLength, IntPtr packageFullName);
+}