simplified field ordering

input/forms.py

@@ -68,25 +68,24 @@ class CommonOrderMixin(forms.Form):
     def __init__(self, *args, **kwargs):
         """
         Override the default form initialization to reorder fields.
+
         The method:
-          1. Collects all existing field names.
-          2. Puts the 'head' fields first (if they exist in this form).
-          3. Keeps all other fields in the middle.
-          4. Puts the 'tail' fields last (if they exist in this form).
+          1. Put the 'head' fields first.
+          2. Put all other fields in the middle.
+          3. Put the 'tail' fields last.
+
+        Non-existing fields are ignored by `order_fields`.
         """
+
         super().__init__(*args, **kwargs)
 
-        existing = list(self.fields.keys())
+        ordered = {*self.field_order_head, *self.field_order_tail}
 
-        # Select only fields that actually exist in this form
-        head = [f for f in self.field_order_head if f in self.fields]
-        tail = [f for f in self.field_order_tail if f in self.fields]
-
-        # All other fields that are not explicitly in head or tail
-        middle = [f for f in existing if f not in (*head, *tail)]
-
-        # Apply the new order to the form fields
-        self.order_fields(head + middle + tail)
+        self.order_fields([
+            *self.field_order_head,
+            *[field for field in self.fields if field not in ordered],
+            *self.field_order_tail,
+        ])
 
 
 class ExternForm(FdbForm):