fix(core): improve shutdown cleanup, socket/stream robustness, and memory/cache handling

ts/security/classes.contentscanner.ts

@@ -182,7 +182,14 @@ export class ContentScanner {
     }
     return ContentScanner.instance;
   }
-  
+
+  /**
+   * Reset the singleton instance (for shutdown/testing)
+   */
+  public static resetInstance(): void {
+    ContentScanner.instance = undefined;
+  }
+
   /**
    * Scan an email for malicious content
    * @param email The email to scan