fix: tighten WeChat session rotation and defer snapshot refresh

Use session snapshot message counts alongside WeChat route counts so long-lived dedicated sessions rotate before Goose history bloats, and refresh snapshots asynchronously so customer replies are not blocked.

Co-authored-by: Cursor <cursoragent@cursor.com>

user-auth.mjs

@@ -2274,6 +2274,18 @@ export function createUserAuth(pool, options = {}) {
     return Number(rows?.[0]?.count ?? 0);
   };
 
+  const getWechatAgentSessionSnapshotMessageCount = async (agentSessionId) => {
+    if (!agentSessionId) return 0;
+    const [rows] = await pool.query(
+      `SELECT synced_msg_count
+       FROM h5_session_snapshots
+       WHERE agent_session_id = ?
+       LIMIT 1`,
+      [agentSessionId],
+    );
+    return Number(rows?.[0]?.synced_msg_count ?? 0);
+  };
+
   const recordWechatMpMessage = async ({
     appId,
     openid,
@@ -2861,6 +2873,7 @@ export function createUserAuth(pool, options = {}) {
     clearWechatAgentRoute,
     touchWechatAgentRoute,
     countWechatAgentSessionMessages,
+    getWechatAgentSessionSnapshotMessageCount,
     recordWechatMpMessage,
     finishWechatMpMessage,
     insertWechatMpMessageDetail,