Apply numbering only to non-normalized files by default

Also add `-f` to force numbering

bin/nn

@@ -190,10 +190,13 @@ def build_plan(files, parse_mode):
     return plan
 
 
-def build_number_plan(files, parse_mode):
+def build_number_plan(files, parse_mode, force=False):
     """Build a rename plan using sequential numbering per day."""
     entries = []
     for file_path in files:
+        if not force and NORMALIZED.match(file_path.name):
+            entries.append((file_path, None, STATUS_ALREADY))
+            continue
         date_str = get_date_for_file(file_path, parse_mode)
         entries.append((file_path, date_str))
 
@@ -201,7 +204,11 @@ def build_number_plan(files, parse_mode):
     plan = []
     seen_targets = {}
 
-    for file_path, date_str in entries:
+    for entry in entries:
+        if len(entry) == 3:
+            plan.append((entry[0], None, entry[2]))
+            continue
+        file_path, date_str = entry
         if date_str is None:
             plan.append((file_path, None, STATUS_NO_MATCH))
             continue
@@ -289,9 +296,16 @@ def main():
         action='store_true',
         help=(
             'Discard original filename stems and number files sequentially '
-            'per day. Combines with --parse to select the date source.'
+            'per day. Combines with --parse to select the date source. '
+            'Skips already-normalized files unless --force is given.'
         ),
     )
+    parser.add_argument(
+        '-f',
+        '--force',
+        action='store_true',
+        help='Force numbering even for already-normalized files (used with -n).',
+    )
     parser.add_argument(
         'files',
         nargs='*',
@@ -306,7 +320,7 @@ def main():
         sys.exit(0)
 
     if args.number:
-        plan = build_number_plan(files, args.parse)
+        plan = build_number_plan(files, args.parse, args.force)
     else:
         plan = build_plan(files, args.parse)
     print_preview(plan)