feat(pay): content cashier coupon and rebate discount chain

Wire zibll-style cash content discounts: VIP list price → buyer 推广折扣 → coupon, then commission on final pay. Reuse AKSRT_Coupon, add Invite::get_referrer, cashier UI, and paid-time coupon burn + rebate_log.

inc/helpers/aksrt-pay.php

@@ -491,6 +491,74 @@ if (!function_exists('aksrt_get_user_pay_price')) {
     }
 }
 
+/**
+ * Whether content cashier may accept coupons for this post (zibll coupon_post_s || coupon_s).
+ */
+if (!function_exists('aksrt_is_content_coupon_allowed')) {
+    function aksrt_is_content_coupon_allowed($post = null): bool {
+        $meta = function_exists('aksrt_get_pay_meta') ? aksrt_get_pay_meta($post) : [];
+        if (!empty($meta['coupon_s'])) {
+            return true;
+        }
+        if (class_exists('AKSRT_Settings') && method_exists('AKSRT_Settings', 'get_content_coupon_settings')) {
+            $cfg = AKSRT_Settings::get_content_coupon_settings();
+            return !empty($cfg['enabled']);
+        }
+        if (class_exists('AKSRT_Settings') && method_exists('AKSRT_Settings', 'get_paid_content_settings')) {
+            $paid = AKSRT_Settings::get_paid_content_settings();
+            return !empty($paid['coupon_post_s']);
+        }
+        return false;
+    }
+}
+
+/**
+ * Buyer-facing 推广折扣 amount for a post (0 if no eligible referrer).
+ * Cash only; mirrors zibpay_get_post_rebate_discount.
+ */
+if (!function_exists('aksrt_get_post_rebate_discount')) {
+    function aksrt_get_post_rebate_discount($post = null, int $user_id = 0): float {
+        $meta = function_exists('aksrt_get_pay_meta') ? aksrt_get_pay_meta($post) : [];
+        $fixed = max(0.0, (float) ($meta['pay_rebate_discount'] ?? 0));
+        if ($fixed <= 0) {
+            return 0.0;
+        }
+        if (!class_exists('AKSRT_Settings') || !method_exists('AKSRT_Settings', 'get_payment_affiliate_settings')) {
+            return 0.0;
+        }
+        $aff = AKSRT_Settings::get_payment_affiliate_settings();
+        if (empty($aff['enabled'])) {
+            return 0.0;
+        }
+        $uid = $user_id > 0 ? $user_id : (function_exists('get_current_user_id') ? (int) get_current_user_id() : 0);
+        $referrer_id = 0;
+        if (class_exists('AKSRT_Invite') && method_exists(AKSRT_Invite::get_instance(), 'get_referrer')) {
+            $referrer_id = (int) AKSRT_Invite::get_instance()->get_referrer($uid);
+        }
+        if ($referrer_id <= 0) {
+            return 0.0;
+        }
+        // Need a positive ratio for referrer (VIP tier of referrer preferred).
+        $ratio = (int) ($aff['ratio'] ?? 0);
+        $user_ratio = is_array($aff['user_ratio'] ?? null) ? $aff['user_ratio'] : [];
+        $ref_vip = 0;
+        if (function_exists('aksrt_get_user_vip_level')) {
+            $ref_vip = (int) aksrt_get_user_vip_level($referrer_id);
+        }
+        if ($ref_vip >= 2 && !empty($user_ratio['vip2'])) {
+            $ratio = (int) $user_ratio['vip2'];
+        } elseif ($ref_vip >= 1 && !empty($user_ratio['vip1'])) {
+            $ratio = (int) $user_ratio['vip1'];
+        } elseif (isset($user_ratio['user'])) {
+            $ratio = (int) $user_ratio['user'];
+        }
+        if ($ratio <= 0) {
+            return 0.0;
+        }
+        return round($fixed, 2);
+    }
+}
+
 // ============================================================
 // 状态判断
 // ============================================================