diff --git a/engine.py b/engine.py
index 755f0c8..70ad56a 100644
--- a/engine.py
+++ b/engine.py
@@ -12,15 +12,18 @@ class SorterEngine:
         """Initializes SQLite tables for Profiles, Folder IDs, and Categories."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
-        # Profiles: Stores Discovery and Review paths
+        
+        # Table 1: Profiles - Stores all discovery, review, and output paths
         cursor.execute('''CREATE TABLE IF NOT EXISTS profiles 
             (name TEXT PRIMARY KEY, disc_t TEXT, rev_t TEXT, rev_c TEXT, path_out TEXT, mode TEXT)''')
-        # Folder IDs: Maps source folders to unique numeric IDs
+        
+        # Table 2: Folder IDs - Maps source paths to unique numeric IDs for renaming
         cursor.execute('''CREATE TABLE IF NOT EXISTS folder_ids (path TEXT PRIMARY KEY, folder_id INTEGER)''')
-        # Categories: Stores the list of sorting categories from your script
+        
+        # Table 3: Categories - Stores the sorting buttons for Tab 4
         cursor.execute('''CREATE TABLE IF NOT EXISTS categories (name TEXT PRIMARY KEY)''')
         
-        # Seed default categories if empty
+        # Seed default categories if the table is new
         cursor.execute("SELECT COUNT(*) FROM categories")
         if cursor.fetchone()[0] == 0:
             for cat in ["_TRASH", "Default", "Action", "Solo"]:
@@ -31,24 +34,27 @@ class SorterEngine:
 
     @staticmethod
     def get_folder_id(source_path):
-        """Retrieves or generates a unique ID for a folder."""
+        """Retrieves or generates a persistent unique ID for a folder."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("SELECT folder_id FROM folder_ids WHERE path = ?", (source_path,))
         result = cursor.fetchone()
+        
         if result:
             fid = result[0]
         else:
             cursor.execute("SELECT MAX(folder_id) FROM folder_ids")
             row = cursor.fetchone()
-            fid = (row[0] + 1) if row[0] else 1
+            fid = (row[0] + 1) if row and row[0] else 1
             cursor.execute("INSERT INTO folder_ids VALUES (?, ?)", (source_path, fid))
             conn.commit()
+            
         conn.close()
         return fid
 
     @staticmethod
     def get_categories():
+        """Fetches the category list for dynamic button rendering."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("SELECT name FROM categories ORDER BY name ASC")
@@ -58,6 +64,7 @@ class SorterEngine:
 
     @staticmethod
     def add_category(name):
+        """Adds a new persistent category to the database."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("INSERT OR IGNORE INTO categories VALUES (?)", (name,))
@@ -66,6 +73,7 @@ class SorterEngine:
 
     @staticmethod
     def save_profile(name, disc_t, rev_t, rev_c, path_out, mode):
+        """Persists the entire path configuration to the database."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("INSERT OR REPLACE INTO profiles VALUES (?, ?, ?, ?, ?, ?)", 
@@ -75,6 +83,7 @@ class SorterEngine:
 
     @staticmethod
     def load_profiles():
+        """Loads all saved path presets."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("SELECT * FROM profiles")
@@ -84,21 +93,24 @@ class SorterEngine:
 
     @staticmethod
     def delete_profile(name):
+        """Removes a profile from the database."""
         conn = sqlite3.connect(SorterEngine.DB_PATH)
         cursor = conn.cursor()
         cursor.execute("DELETE FROM profiles WHERE name = ?", (name,))
         conn.commit()
         conn.close()
 
-    # --- Standard File Operations ---
+    # --- File Operations ---
     @staticmethod
     def get_images(path):
+        """Standard image scanning for directories."""
         exts = ('.jpg', '.jpeg', '.png', '.webp', '.bmp', '.tiff')
         if not path or not os.path.exists(path): return []
         return sorted([f for f in os.listdir(path) if f.lower().endswith(exts)])
 
     @staticmethod
     def harmonize_names(t_p, c_p):
+        """Forces the control file to match the target name to fix ID collisions."""
         t_name = os.path.basename(t_p)
         new_c_p = os.path.join(os.path.dirname(c_p), t_name)
         if os.path.exists(new_c_p) and c_p != new_c_p:
@@ -109,9 +121,19 @@ class SorterEngine:
 
     @staticmethod
     def compress_for_web(path, quality):
+        """Converts raw images to compressed JPEGs for fast browser loading."""
         try:
             with Image.open(path) as img:
                 buf = BytesIO()
                 img.convert("RGB").save(buf, format="JPEG", quality=quality)
                 return buf
-        except: return None
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+        except: return None
+
+    @staticmethod
+    def revert_action(action):
+        """Undoes the last move operation by reversing source and destination."""
+        if action['type'] in ['link_standard', 'link_solo', 'unused', 'cat_move']:
+            if os.path.exists(action['t_dst']): shutil.move(action['t_dst'], action['t_src'])
+            if 'c_dst' in action and os.path.exists(action['c_dst']):
+                if 'link' in action['type']: os.remove(action['c_dst'])
+                else: shutil.move(action['c_dst'], action['c_src'])
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