fix(forum): accept plate CPT IDs when creating topics

Compose UI and board search already send aksrt_forum_plate post IDs as
board_id, but create_topic still validated aksrt_forum_board term IDs and
never wrote _aksrt_plate_id — so real plates failed with 版块不存在.
Validate/store under the plate model (and fix move_board the same way).

src/AKSRT/Forum/TopicService.php

@@ -100,9 +100,9 @@ class TopicService {
         // §7.3: Strip unauthorized media from content based on compose capabilities
         $content = $this->sanitize_topic_content($user_id, $content);
 
-        $board = get_term($board_id, 'aksrt_forum_board');
-        if (!$board || is_wp_error($board)) {
-            return new \WP_Error('invalid_board', __('版块不存在', 'aksrt'));
+        $board_ok = $this->assert_board($board_id);
+        if (is_wp_error($board_ok)) {
+            return $board_ok;
         }
 
         if (!isset($this->get_visibility_map()[$visibility])) {
@@ -125,7 +125,7 @@ class TopicService {
             return $post_id;
         }
 
-        wp_set_object_terms($post_id, [$board_id], 'aksrt_forum_board');
+        $this->attach_topic_to_board((int) $post_id, $board_id);
 
         $clean_tags = array_values(array_filter(array_map('sanitize_text_field', $tags)));
         if (count($clean_tags) > 5) {
@@ -198,12 +198,60 @@ class TopicService {
     }
 
     // ================================================================
-    // Topic moderation
+    // Board / plate attachment helpers
     // ================================================================
 
     /**
-     * Moderate topic.
+     * Validate board_id as plate CPT post ID when plate is active, else taxonomy term.
      *
-     * @return array<string,mixed>|\WP_Error
+     * @return true|\WP_Error
      */
+    private function assert_board(int $board_id, string $error_message = '') {
+        if ($error_message === '') {
+            $error_message = __('版块不存在', 'aksrt');
+        }
+
+        if ($board_id <= 0) {
+            return new \WP_Error('invalid_board', $error_message);
+        }
+
+        if ($this->forum->is_plate_cpt_active()) {
+            $post = get_post($board_id);
+            if (!$post || $post->post_type !== 'aksrt_forum_plate' || $post->post_status !== 'publish') {
+                return new \WP_Error('invalid_board', $error_message);
+            }
+            return true;
+        }
+
+        $board = get_term($board_id, 'aksrt_forum_board');
+        if (!$board || is_wp_error($board)) {
+            return new \WP_Error('invalid_board', $error_message);
+        }
+
+        return true;
+    }
+
+    /**
+     * Attach a topic to a board.
+     * Plate CPT active: store `_aksrt_plate_id` only (native association).
+     * Otherwise: taxonomy term on aksrt_forum_board.
+     */
+    private function attach_topic_to_board(int $topic_id, int $board_id): void {
+        if ($topic_id <= 0 || $board_id <= 0) {
+            return;
+        }
+
+        if ($this->forum->is_plate_cpt_active()) {
+            update_post_meta($topic_id, '_aksrt_plate_id', $board_id);
+            return;
+        }
+
+        if (taxonomy_exists('aksrt_forum_board')) {
+            wp_set_object_terms($topic_id, [$board_id], 'aksrt_forum_board');
+        }
+    }
+
+    // ================================================================
+    // Topic moderation
+    // ================================================================
 }

src/AKSRT/Forum/TopicServicePart1.php

@@ -25,17 +25,29 @@ trait TopicServicePart1 {
         switch ($action) {
             case 'move_board':
                 $target_board_id = (int) ($payload['target_board_id'] ?? 0);
-                $target_board = get_term($target_board_id, 'aksrt_forum_board');
-                if (!$target_board || is_wp_error($target_board)) {
-                    return new \WP_Error('invalid_board', __('目标版块不存在', 'aksrt'));
+                $target_ok = $this->assert_board($target_board_id, __('目标版块不存在', 'aksrt'));
+                if (is_wp_error($target_ok)) {
+                    return $target_ok;
                 }
 
-                $current_board_ids = wp_get_post_terms($topic_id, 'aksrt_forum_board', ['fields' => 'ids']);
-                wp_set_object_terms($topic_id, [$target_board_id], 'aksrt_forum_board');
-                foreach ($current_board_ids as $current_board_id) {
-                    $this->forum->sync_board_count((int) $current_board_id);
+                if ($this->forum->is_plate_cpt_active()) {
+                    $previous_plate_id = (int) $this->forum->get_topic_plate_id($topic_id);
+                    $this->attach_topic_to_board($topic_id, $target_board_id);
+                    if ($previous_plate_id > 0 && $previous_plate_id !== $target_board_id) {
+                        $this->forum->sync_board_count($previous_plate_id);
+                    }
+                    $this->forum->sync_board_count($target_board_id);
+                } else {
+                    $current_board_ids = wp_get_post_terms($topic_id, 'aksrt_forum_board', ['fields' => 'ids']);
+                    if (is_wp_error($current_board_ids)) {
+                        $current_board_ids = [];
+                    }
+                    $this->attach_topic_to_board($topic_id, $target_board_id);
+                    foreach ($current_board_ids as $current_board_id) {
+                        $this->forum->sync_board_count((int) $current_board_id);
+                    }
+                    $this->forum->sync_board_count($target_board_id);
                 }
-                $this->forum->sync_board_count($target_board_id);
                 break;
 
             case 'visibility':