fix(forum): return JSON on draft AJAX fatals

Partial deploys still 500 HTML via draft_service; catch Throwable and
wp_send_json_error so the client can show the real exception message.

src/AKSRT/Forum/Forum.php

@@ -88,6 +88,13 @@ class Forum {
 
     private function draft_service(): DraftService {
         if (!$this->draft_svc) {
+            // Composer PSR-4: AKSRT\Forum\DraftService → src/AKSRT/Forum/DraftService.php
+            // Never require legacy class-aksrt-forum-draft-service.php.
+            if (!class_exists(DraftService::class, true)) {
+                throw new \RuntimeException(
+                    'AKSRT\\Forum\\DraftService missing; deploy src/AKSRT/Forum/DraftService.php and run composer dump-autoload if needed'
+                );
+            }
             $this->draft_svc = new DraftService($this);
         }
         return $this->draft_svc;
@@ -777,15 +784,47 @@ class Forum {
     }
 
     public function ajax_save_draft(): void {
-        $this->draft_service()->ajax_save_draft();
+        $this->run_draft_ajax(static function (self $forum): void {
+            $forum->draft_service()->ajax_save_draft();
+        });
     }
 
     public function ajax_load_draft(): void {
-        $this->draft_service()->ajax_load_draft();
+        $this->run_draft_ajax(static function (self $forum): void {
+            $forum->draft_service()->ajax_load_draft();
+        });
     }
 
     public function ajax_delete_draft(): void {
-        $this->draft_service()->ajax_delete_draft();
+        $this->run_draft_ajax(static function (self $forum): void {
+            $forum->draft_service()->ajax_delete_draft();
+        });
+    }
+
+    /**
+     * Draft AJAX must never leak WP recovery HTML — return JSON on Throwable.
+     */
+    private function run_draft_ajax(callable $callback): void {
+        try {
+            $callback($this);
+        } catch (\Throwable $e) {
+            if (defined('WP_DEBUG') && WP_DEBUG) {
+                error_log('[AKSRT forum draft ajax] ' . $e->getMessage() . ' @ ' . $e->getFile() . ':' . $e->getLine());
+            }
+            // Prefer JSON even when autoload/require still broken on a partial deploy.
+            if (!headers_sent()) {
+                status_header(500);
+            }
+            wp_send_json_error([
+                'message' => sprintf(
+                    /* translators: %s: exception message */
+                    __('草稿操作失败：%s', 'aksrt'),
+                    $e->getMessage()
+                ),
+                'file'    => basename($e->getFile()),
+                'line'    => $e->getLine(),
+            ], 500);
+        }
     }
 
     public function ajax_search_boards(): void {