Add drag-and-drop file support for macOS guests

Sources/tart/CI/CI.swift

@@ -5,6 +5,15 @@ struct CI {
     rawVersion.expanded() ? rawVersion : "SNAPSHOT"
   }
 
+  /// Same as `version`, but always a valid semver with major ≥ 2 so the guest
+  /// agent's `/dev/cu.tart-version-<semver>` Tart-detection probe accepts it.
+  /// For non-tagged dev builds we'd otherwise emit `SNAPSHOT`, which the agent
+  /// can't parse — it then thinks it isn't running on Tart and bails out with
+  /// "operation not permitted" when it tries to SIGTERM its launchd parent.
+  static var deviceVersion: String {
+    rawVersion.expanded() ? rawVersion : "99.0.0"
+  }
+
   static var release: String? {
     rawVersion.expanded() ? "tart@\(rawVersion)" : nil
   }