fix(node): reuse session ID in external storage example (#1035)

The previous example generated a new UUID on every wrap() call.
This breaks RSC environments where cookies cannot be updated,
causing session loss when the cookie still contains the old ID.

Updated the RedisSessionWrapper example to store and reuse the
session ID from unwrap(), ensuring the cookie value remains stable
while external storage data can be updated.

Author: wangsijie

packages/node/README.md

@@ -86,10 +86,16 @@ But the cookie size is limited, so you may need to use external storage like Red
 import { CookieStorage } from '@logto/node';
 
 class RedisSessionWrapper implements SessionWrapper {
+  private currentSessionId?: string;
+
   constructor(private readonly redis: Redis) {}
 
   async wrap(data: unknown, _key: string): Promise<string> {
-    const sessionId = randomUUID();
+    // Reuse existing session ID if available, only generate new one for first-time users.
+    // This is important for environments where cookies cannot be updated (e.g. React Server Components),
+    // as the session ID in the cookie must remain stable while the data in Redis can be updated.
+    const sessionId = this.currentSessionId ?? randomUUID();
+    this.currentSessionId = sessionId;
     await this.redis.set(`logto_session_${sessionId}`, JSON.stringify(data));
     return sessionId;
   }
@@ -99,8 +105,10 @@ class RedisSessionWrapper implements SessionWrapper {
       return {};
     }
 
+    // Store the session ID for potential reuse in wrap()
+    this.currentSessionId = value;
     const data = await this.redis.get(`logto_session_${value}`);
-    return JSON.parse(data);
+    return data ? JSON.parse(data) : {};
   }
 }