perf(user): 关注结算异步化并去除冗余勋章评估

src/User/BadgeAutoAward.php

@@ -59,12 +59,12 @@ class BadgeAutoAward {
 	}
 
 	public function on_follow(int $follower_id, int $following_id): void {
+		unset($follower_id);
+		// No medal metric depends on how many users someone follows, so only
+		// the followed user (whose follower count changed) can earn here.
 		if ($following_id > 0) {
 			$this->evaluate($following_id);
 		}
-		if ($follower_id > 0) {
-			$this->evaluate($follower_id);
-		}
 	}
 
 	public function on_checkin(int $user_id): void {

src/User/Follow.php

@@ -47,10 +47,24 @@ class Follow {
         if ($result === false) {
             return false;
         }
-        do_action('aksrt_user_followed', $follower_id, $following_id);
+        self::defer_action('aksrt_user_followed', $follower_id, $following_id);
         return true;
     }
 
+    /**
+     * 在响应送达客户端之后再触发结算钩子（积分/勋章/等级），
+     * 避免重度订阅者阻塞关注接口。非 PHP-FPM 环境退化为
+     * shutdown 时机同步执行，行为与直接 do_action 等价。
+     */
+    private static function defer_action(string $hook, int ...$args): void {
+        register_shutdown_function(static function () use ($hook, $args): void {
+            if (function_exists('fastcgi_finish_request')) {
+                fastcgi_finish_request();
+            }
+            do_action($hook, ...$args);
+        });
+    }
+
     /**
      * 取消关注
      */

src/User/Metrics.php

@@ -31,7 +31,6 @@ class Metrics {
 		add_action('aksrt_post_liked', [$this, 'on_post_liked'], 20, 3);
 		add_action('aksrt_comment_liked', [$this, 'on_comment_liked'], 20, 3);
 		add_action('aksrt_post_favorited', [$this, 'on_post_favorited'], 20, 3);
-		add_action('aksrt_user_followed', [$this, 'on_user_followed'], 20, 2);
 		add_action('aksrt_post_viewed', [$this, 'on_post_viewed'], 20, 2);
 
 		add_action('aksrt_user_signed_in', [$this, 'on_user_signed_in'], 20, 1);
@@ -90,13 +89,6 @@ class Metrics {
 		// Favorite is free-points / level only; no dedicated medal get_type.
 	}
 
-	public function on_user_followed(int $follower_id, int $following_id): void {
-		unset($follower_id);
-		if ($following_id > 0) {
-			self::reevaluate_medals($following_id);
-		}
-	}
-
 	public function on_post_viewed(int $post_id, int $viewer_id = 0): void {
 		unset($viewer_id);
 		$post = get_post($post_id);