feat(auth): M2 POST /wechat/conflict/rebind(换绑=注销X重建Y,单事务)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/api/v1/auth.py

@@ -402,6 +402,44 @@ def wechat_conflict_continue(
     )
 
 
+@router.post(
+    "/wechat/conflict/rebind",
+    response_model=WechatBindResultResponse,
+    summary="微信占用冲突·换绑(注销老账号+用该号重建全新账号)",
+)
+def wechat_conflict_rebind(
+    req: WechatConflictRebindRequest, request: Request, db: DbSession
+) -> WechatBindResultResponse:
+    from app.core.config import settings  # 局部 import,避免循环
+
+    try:
+        claims = decode_conflict_ticket(req.conflict_ticket)
+    except TokenError as e:
+        raise HTTPException(status_code=401, detail="操作超时,请重新用微信登录") from e
+
+    enforce_rate_limit(
+        request, scope="wechat-conflict-device", subject=req.device_id,
+        limit=SMS_LOGIN_MAX_PER_HOUR, window_sec=3600, detail="操作过于频繁,请稍后再试",
+    )
+
+    phone = claims["phone"]
+    if rebind_repo.rebound_within_days(db, phone, settings.PHONE_REBIND_LIMIT_DAYS):
+        days = rebind_repo.remaining_block_days(db, phone, settings.PHONE_REBIND_LIMIT_DAYS)
+        raise HTTPException(status_code=409, detail=f"该手机号 {days} 天内已换绑过,暂不能再次换绑")
+
+    user = user_repo.rebind_account(
+        db, phone=phone, openid=claims["openid"],
+        wechat_nickname=claims["wnk"], wechat_avatar_url=claims["wav"],
+    )
+    completed = onboarding_repo.is_completed(db, user_id=user.id, device_id=req.device_id)
+    logger.info("wechat conflict rebind new_user_id=%d phone=%s openid=%s***",
+                user.id, mask_phone(phone), claims["openid"][:6])
+    return WechatBindResultResponse(
+        status="logged_in",
+        token=_login_response(user, onboarding_completed=completed),
+    )
+
+
 # ===================== Refresh =====================
 
 @router.post("/refresh", response_model=TokenPair, summary="用 refresh_token 换新 token 对")