Resolve #3512812 "Adding and removing"

Closes #3512812

src/Form/DeriverEditForm.php

@@ -88,7 +88,7 @@ class DeriverEditForm extends DeriverFormBase {
 
     // Inline addition of a new deriver.
     // Assume getNewDeriverOptions() returns an array of available derivers.
-    $new_deriver_options = $this->getNewDeriverOptions($form_state); 
+    $new_deriver_options = $this->getNewDeriverOptions($form_state);
     $form['derivers_form_wrapper']['new_deriver'] = [
       '#type' => 'container',
       '#tree' => TRUE, // Preserve nested structure.
@@ -184,10 +184,21 @@ class DeriverEditForm extends DeriverFormBase {
 
   public function submitForm(array &$form, FormStateInterface $form_state) {
     parent::submitForm($form, $form_state);
-    $test = $form_state->get('attached_derivers');
-    // Update the entity with the temporary state.
-    $this->entity->setDerivers($form_state->get('attached_derivers'));
-    // Save the entity only at this point.
+
+    // Retrieve the current temporary state of derivers.
+    $attached_derivers = $form_state->get('attached_derivers');
+    // Get the submitted values for each deriver row (which include the updated weight).
+    $submitted_derivers = $form_state->getValue(['derivers_form_wrapper', 'derivers']);
+
+    // Update the temporary state with the new weight values.
+    foreach ($submitted_derivers as $delta => $values) {
+      if (isset($attached_derivers[$delta])) {
+        $attached_derivers[$delta]['weight'] = $values['weight'];
+      }
+    }
+
+    // Update the entity with the modified derivers and save.
+    $this->entity->setDerivers($attached_derivers);
     $this->entity->save();
     $this->messenger()->addStatus($this->t('Deriver %name has been saved.', ['%name' => $this->entity->label()]));
   }