[9.x] Fix updated_at timestamp not updating when field is read-only

src/Http/Controllers/CP/Traits/PreparesModels.php

@@ -182,6 +182,16 @@ protected function prepareModelForSaving(Resource $resource, Model &$model, Requ
                     return;
                 }
 
+                // Skip read-only timestamp columns so Laravel's automatic
+                // timestamp handling isn't prevented by a stale value.
+                if (
+                    $field->visibility() === 'read_only'
+                    && $model->usesTimestamps()
+                    && in_array($field->handle(), [$model->getCreatedAtColumn(), $model->getUpdatedAtColumn()])
+                ) {
+                    return;
+                }
+
                 $model->setAttribute($field->handle(), $processedValue);
             });
     }

tests/Http/Controllers/CP/ResourceControllerTest.php

@@ -678,7 +678,47 @@ public function can_update_resource_and_ensure_computed_field_isnt_saved_to_data
     }
 
     #[Test]
-    public function can_update_resource_and_ensure__field_isnt_saved_to_database()
+    public function can_update_resource_and_ensure_read_only_timestamp_field_doesnt_prevent_timestamp_update()
+    {
+        $postBlueprint = Blueprint::find('runway::post');
+
+        Blueprint::shouldReceive('find')->with('user')->andReturn(new \Statamic\Fields\Blueprint);
+        Blueprint::shouldReceive('find')->with('runway::author')->andReturn(new \Statamic\Fields\Blueprint);
+        Blueprint::shouldReceive('find')->with('runway::post')->andReturn($postBlueprint->ensureField('updated_at', [
+            'type' => 'date',
+            'time_enabled' => true,
+            'visibility' => 'read_only',
+        ]));
+        Blueprint::shouldReceive('getAdditionalNamespaces')->andReturn(collect(['runway' => base_path('resources/blueprints/runway')]))->zeroOrMoreTimes();
+
+        $post = Post::factory()->create();
+        $user = User::make()->makeSuper()->save();
+
+        $originalUpdatedAt = $post->updated_at;
+
+        $this->travel(5)->minutes();
+
+        $this
+            ->actingAs($user)
+            ->patch(cp_route('runway.update', ['resource' => 'post', 'model' => $post->id]), [
+                'published' => true,
+                'title' => 'Santa is coming home',
+                'slug' => 'santa-is-coming-home',
+                'body' => $post->body,
+                'author_id' => [$post->author_id],
+                'updated_at' => $originalUpdatedAt->toIso8601ZuluString('millisecond'),
+            ])
+            ->assertOk()
+            ->assertJsonStructure(['data', 'saved']);
+
+        $post->refresh();
+
+        $this->assertEquals('Santa is coming home', $post->title);
+        $this->assertTrue($post->updated_at->gt($originalUpdatedAt));
+    }
+
+    #[Test]
+    public function can_update_resource_and_ensure_field_with_save_false_isnt_saved_to_database()
     {
         $post = Post::factory()->create();
         $user = User::make()->makeSuper()->save();