feat(auth): M3 §10 绑微信按默认替换展示昵称头像(共享 helper 接两路径)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/repositories/user.py

@@ -59,6 +59,17 @@ def is_default_nickname(nickname: str | None) -> bool:
     )
 
 
+def apply_wechat_display_identity(
+    user: User, *, wechat_nickname: str | None, wechat_avatar_url: str | None
+) -> None:
+    """§10:用已有账号绑微信时,仅当展示字段仍为默认才用微信昵称/头像替换(两规则独立);
+    自定义(改过昵称/传过头像)则保留。只改内存对象,由调用方 commit。"""
+    if is_default_nickname(user.nickname) and wechat_nickname:
+        user.nickname = wechat_nickname
+    if user.avatar_url is None and wechat_avatar_url:
+        user.avatar_url = wechat_avatar_url
+
+
 def get_user_by_username(db: Session, username: str) -> User | None:
     return db.execute(
         select(User).where(User.username == username)
@@ -105,14 +116,16 @@ def attach_wechat_to_user(
 ) -> User:
     """继续绑定:把微信 openid + 微信源字段并入已存在账号(调用方保证 user.wechat_openid 为空)。
 
-    **只写 wechat_openid / wechat_nickname / wechat_avatar_url,不动展示 nickname/avatar_url**
-    (完整 §10"默认则用微信、改过则保留"规则留 M3)。撞 openid 唯一约束(O 期间被别处绑走,
-    极罕见)时由调用方捕获 IntegrityError 兜底降级为"只登入不绑"。
+    写 wechat_openid / wechat_nickname / wechat_avatar_url,并按 §10 规则回填展示字段:
+    仅当昵称仍为默认值(is_default_nickname)时用微信昵称替换,仅当头像为 null 时用微信头像替换;
+    用户已自定义的展示昵称/头像始终保留,两规则相互独立。
+    撞 openid 唯一约束(O 期间被别处绑走,极罕见)时由调用方捕获 IntegrityError 兜底降级为"只登入不绑"。
     """
     user.wechat_openid = openid
     user.wechat_nickname = wechat_nickname
     user.wechat_avatar_url = wechat_avatar_url
     user.last_login_at = datetime.now(timezone.utc)
+    apply_wechat_display_identity(user, wechat_nickname=wechat_nickname, wechat_avatar_url=wechat_avatar_url)
     db.commit()
     db.refresh(user)
     return user

app/repositories/wallet.py

@@ -20,6 +20,7 @@ from app.core.config import settings
 from app.core.rewards import COIN_PER_CENT, coins_to_cents
 from app.integrations import wxpay
 from app.models.user import User
+from app.repositories.user import apply_wechat_display_identity
 from app.models.wallet import (
     CashTransaction,
     CoinAccount,
@@ -374,6 +375,7 @@ def bind_wechat_openid(db: Session, user_id: int, code: str) -> dict:
     user.wechat_openid = info["openid"]
     user.wechat_nickname = info["nickname"]
     user.wechat_avatar_url = info["avatar_url"]
+    apply_wechat_display_identity(user, wechat_nickname=info["nickname"], wechat_avatar_url=info["avatar_url"])
     db.commit()
     return info