fix(autoload): canary DomainModel after Composer load

Stale vendor/ after the PSR-4 cutover omits AKSRT\ from
autoload_psr4, so helpers fatal on DomainModel constants.
Fail loud with composer install/dump-autoload guidance and
document the deploy step in README + ADR.

functions.php

@@ -63,18 +63,32 @@ if (!function_exists('aksrt_get_setting')) {
 }
 
 // ============================================================
-// 加载 Composer 依赖（OAuth2 客户端库等）
+// 加载 Composer 依赖（第三方库 + 主题 PSR-4：AKSRT\ → src/AKSRT/）
 // ============================================================
 $composer_autoload = AKSRT_DIR . '/vendor/autoload.php';
 if (!file_exists($composer_autoload)) {
     wp_die(
-        esc_html__('AKSRT requires Composer dependencies. Run composer install in the theme directory.', 'aksrt'),
+        esc_html__('AKSRT requires Composer dependencies. Run "composer install" in the theme directory.', 'aksrt'),
         esc_html__('AKSRT theme', 'aksrt'),
         ['response' => 500]
     );
 }
 require_once $composer_autoload;
 
+// Theme classes live under src/AKSRT/ and only load via Composer PSR-4.
+// Stale vendor/ (e.g. install before composer.json gained "AKSRT\\") leaves
+// autoload_psr4 without AKSRT\ and fatals on the first DomainModel reference.
+if (!class_exists(\AKSRT\Core\DomainModel::class, true)) {
+    wp_die(
+        esc_html__(
+            'AKSRT class autoload is incomplete: AKSRT\\Core\\DomainModel was not found. In the theme directory run "composer install" (or "composer dump-autoload -o"), then clear any opcode cache (opcache_reset / php-fpm reload).',
+            'aksrt'
+        ),
+        esc_html__('AKSRT theme', 'aksrt'),
+        ['response' => 500]
+    );
+}
+
 // ============================================================
 // 加载 Bootstrap（辅助函数 → 类文件 → 核心钩子）
 // ============================================================