Fix project config ordering for partial loaded elementSources entries

Applying project config to a clean install only sorted keys by depth.
This allowed `sections` changes to run before related
`elementSources` entries were fully built. Resulting in the error:

    In ElementSources.php line 147:

      Undefined array key "type"

Sort pending changes by top-level key first, then by depth within each
group. This makes sure only complete elements are applied.

Author: wvell

src/services/ProjectConfig.php

@@ -1486,8 +1486,16 @@ private function _getPendingChanges(?array $configData = null, bool $existsOnly
 
         unset($removedItem);
 
-        // Sort by number of dots to ensure deepest paths listed first
+        // Sort by top-level key first, then deepest paths first within each group.
         $sorter = function($a, $b) {
+            $aTop = explode('.', $a, 2)[0];
+            $bTop = explode('.', $b, 2)[0];
+            $topCmp = strcmp($aTop, $bTop);
+
+            if ($topCmp !== 0) {
+                return $topCmp;
+            }
+
             $aDepth = ProjectConfigHelper::pathDepth($a);
             $bDepth = ProjectConfigHelper::pathDepth($b);
             return $bDepth <=> $aDepth;

tests/unit/services/ProjectConfigTest.php

@@ -9,7 +9,9 @@
 
 use Codeception\Stub\Expected;
 use Craft;
+use craft\elements\Category;
 use craft\helpers\StringHelper;
+use craft\models\ProjectConfigData;
 use craft\models\ReadOnlyProjectConfigData;
 use craft\mutex\Mutex;
 use craft\mutex\NullMutex;
@@ -216,6 +218,69 @@ public function testEventsFiredAndDeltaStored(): void
         $pc->saveModifiedConfigData();
     }
 
+    public function testApplyingConfigChangesDoesNotExposePartialElementSourcesToSectionHandlers(): void
+    {
+        $projectConfig = new ProjectConfig();
+        $internalConfig = new ReadOnlyProjectConfigData([], $projectConfig);
+        $currentWorkingConfig = new ProjectConfigData([], $projectConfig);
+
+        $internalConfigProperty = new \ReflectionProperty(ProjectConfig::class, '_internalConfig');
+        $internalConfigProperty->setValue($projectConfig, $internalConfig);
+
+        $currentWorkingConfigProperty = new \ReflectionProperty(ProjectConfig::class, '_currentWorkingConfig');
+        $currentWorkingConfigProperty->setValue($projectConfig, $currentWorkingConfig);
+
+        $incomingConfig = [
+            'elementSources' => [
+                'craft\\elements\\Category' => [[
+                    'defaultSort' => ['structure', 'asc'],
+                    'tableAttributes' => ['link'],
+                    'type' => 'native',
+                    'key' => 'group:bedad454-861f-4d7f-b0f6-40ce023cffc5',
+                    'disabled' => false,
+                ]],
+            ],
+            'sections' => [
+                'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa' => [
+                    'siteSettings' => [
+                        'bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb' => [
+                            'hasUrls' => true,
+                            'uriFormat' => 'test/{slug}',
+                            'template' => 'test/_entry',
+                            'enabledByDefault' => true,
+                        ],
+                    ],
+                    'entryTypes' => ['cccccccc-cccc-cccc-cccc-cccccccccccc'],
+                ],
+            ],
+        ];
+
+        $externalConfig = new ReadOnlyProjectConfigData($incomingConfig, $projectConfig);
+        $externalConfigProperty = new \ReflectionProperty(ProjectConfig::class, '_externalConfig');
+        $externalConfigProperty->setValue($projectConfig, $externalConfig);
+
+        $originalProjectConfig = Craft::$app->getProjectConfig();
+        $originalElementSources = Craft::$app->getElementSources();
+        $handlerWasCalled = false;
+
+        Craft::$app->set('projectConfig', $projectConfig);
+        Craft::$app->set('elementSources', new \craft\services\ElementSources());
+
+        $projectConfig->onAdd(ProjectConfig::PATH_SECTIONS . '.{uid}', function() use (&$handlerWasCalled) {
+            $handlerWasCalled = true;
+            Craft::$app->getElementSources()->getSources(Category::class);
+        });
+
+        try {
+            $projectConfig->applyConfigChanges($incomingConfig);
+        } finally {
+            Craft::$app->set('projectConfig', $originalProjectConfig);
+            Craft::$app->set('elementSources', $originalElementSources);
+        }
+
+        self::assertTrue($handlerWasCalled);
+    }
+
     public function getConfigProvider(): array
     {
         return [