Restructure solution layout by module

src/Cli/StellaOps.Cli/Plugins/RestartOnlyCliPluginGuard.cs

@@ -0,0 +1,41 @@
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading;
+
+namespace StellaOps.Cli.Plugins;
+
+internal sealed class RestartOnlyCliPluginGuard
+{
+    private readonly ConcurrentDictionary<string, byte> _plugins = new(StringComparer.OrdinalIgnoreCase);
+    private bool _sealed;
+
+    public IReadOnlyCollection<string> KnownPlugins => _plugins.Keys.ToArray();
+
+    public bool IsSealed => Volatile.Read(ref _sealed);
+
+    public void EnsureRegistrationAllowed(string pluginPath)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(pluginPath);
+
+        var normalized = Normalize(pluginPath);
+        if (IsSealed && !_plugins.ContainsKey(normalized))
+        {
+            throw new InvalidOperationException($"Plug-in '{pluginPath}' cannot be registered after startup. Restart required.");
+        }
+
+        _plugins.TryAdd(normalized, 0);
+    }
+
+    public void Seal()
+    {
+        Volatile.Write(ref _sealed, true);
+    }
+
+    private static string Normalize(string path)
+    {
+        var full = Path.GetFullPath(path);
+        return full.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);
+    }
+}