diff --git a/app/api/v1/auth.py b/app/api/v1/auth.py
index 0f3ab4c..94b7d70 100644
--- a/app/api/v1/auth.py
+++ b/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")
diff --git a/app/repositories/user.py b/app/repositories/user.py
index 40ce500..2ff768d 100644
--- a/app/repositories/user.py
+++ b/app/repositories/user.py
@@ -12,6 +12,7 @@ from sqlalchemy import select
 from sqlalchemy.orm import Session
 
 from app.models.user import User
+from app.repositories import phone_rebind
 
 
 # ===== 创建时分配的标识:用户名(对外展示账号 ID)+ 默认昵称 =====
@@ -117,7 +118,7 @@ def attach_wechat_to_user(
     return user
 
 
-def create_wechat_user(
+def _build_wechat_user(
     db: Session,
     *,
     phone: str,
@@ -125,12 +126,8 @@ def create_wechat_user(
     wechat_nickname: str | None,
     wechat_avatar_url: str | None,
 ) -> User:
-    """微信登录新建账号:register_channel='wechat';展示昵称/头像取微信(§10 新注册),
-    昵称缺失(微信隐私脱敏返回 None)时退默认昵称。同时保存 wechat_* 源字段。
-
-    openid 唯一约束是并发/重复绑定的最终防线(极罕见,openid 在 wechat-login 刚查过为空)。
-    """
-    now = datetime.now(timezone.utc)
+    """构造并 db.add 一个微信账号行(register_channel='wechat',展示昵称头像取微信,缺则默认),
+    **不 commit**。create_wechat_user 与 rebind_account 共用,保证建号逻辑单一来源。"""
     user = User(
         phone=phone,
         username=_gen_unique_username(db),
@@ -140,9 +137,28 @@ def create_wechat_user(
         wechat_openid=openid,
         wechat_nickname=wechat_nickname,
         wechat_avatar_url=wechat_avatar_url,
-        last_login_at=now,
+        last_login_at=datetime.now(timezone.utc),
     )
     db.add(user)
+    return user
+
+
+def create_wechat_user(
+    db: Session,
+    *,
+    phone: str,
+    openid: str,
+    wechat_nickname: str | None,
+    wechat_avatar_url: str | None,
+) -> User:
+    """微信登录新建账号(未占用分支)。见 _build_wechat_user。
+
+    openid 唯一约束是并发/重复绑定的最终防线(极罕见,openid 在 wechat-login 刚查过为空)。
+    """
+    user = _build_wechat_user(
+        db, phone=phone, openid=openid,
+        wechat_nickname=wechat_nickname, wechat_avatar_url=wechat_avatar_url,
+    )
     db.commit()
     db.refresh(user)
     return user
@@ -216,3 +232,44 @@ def soft_delete_account(db: Session, user: User) -> None:
     # 释放邀请码唯一槽
     user.invite_code = None
     db.commit()
+
+
+def rebind_account(
+    db: Session,
+    *,
+    phone: str,
+    openid: str,
+    wechat_nickname: str | None,
+    wechat_avatar_url: str | None,
+    source: str = "wechat_conflict",
+) -> User:
+    """换绑:**单事务内**注销老账号 X(腾出手机号)+ 用该号建全新微信账号 Y + 写换绑台账。
+
+    - 老账号可能已不存在(P 被腾空)→ old_user_id=None,直接建 Y(幂等更稳)。
+    - 手机号唯一约束靠时序:先把 X.phone 改名并 flush 腾号,再插 Y。
+    - 全程不中途 commit,任一步失败整体回滚,绝不出现"X 删了 Y 没建"。
+    X 的字段变更等价 soft_delete_account(软删 + 匿名化 + 释放 openid/邀请码唯一槽),但不在此 commit。
+    """
+    old = get_user_by_phone(db, phone)
+    old_id = old.id if old is not None else None
+    if old is not None:
+        old.status = "deleted"
+        old.phone = f"deleted_{old.id}"
+        old.nickname = None
+        old.avatar_url = None
+        old.wechat_openid = None
+        old.wechat_nickname = None
+        old.wechat_avatar_url = None
+        old.invite_code = None
+        db.flush()  # 先落 phone 改名,腾出手机号唯一约束,才能给 Y 用
+    new_user = _build_wechat_user(
+        db, phone=phone, openid=openid,
+        wechat_nickname=wechat_nickname, wechat_avatar_url=wechat_avatar_url,
+    )
+    db.flush()  # 拿 new_user.id
+    phone_rebind.add_rebind_log(
+        db, phone=phone, old_user_id=old_id, new_user_id=new_user.id, source=source
+    )
+    db.commit()
+    db.refresh(new_user)
+    return new_user
diff --git a/tests/test_wechat_conflict.py b/tests/test_wechat_conflict.py
index c3ead0e..7ca6d01 100644
--- a/tests/test_wechat_conflict.py
+++ b/tests/test_wechat_conflict.py
@@ -151,3 +151,61 @@ def test_continue_expired_ticket_returns_401(client, monkeypatch) -> None:
         json={"conflict_ticket": expired, "device_id": "devC3"},
     )
     assert r.status_code == 401, r.text
+
+
+# ===== Task 5: 换绑 =====
+
+def test_rebind_creates_new_account_and_binds_openid(client, monkeypatch) -> None:
+    """换绑 → 建全新微信账号 Y(≠X)+ openid 落到 Y;老账号 X 被注销(手机号归 Y)。"""
+    phone = "13900139301"
+    x_id = _sms_occupy(client, phone)
+    body = _occupy_via_conflict(client, monkeypatch, "openid_rb_301", phone, "devR1")
+
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/rebind",
+        json={"conflict_ticket": body["conflict_ticket"], "device_id": "devR1"},
+    )
+    assert r.status_code == 200, r.text
+    y = r.json()["token"]["user"]
+    assert r.json()["status"] == "logged_in"
+    assert y["phone"] == phone
+    assert y["register_channel"] == "wechat"
+    assert y["id"] != x_id  # 是全新账号,不是老账号
+
+    # openid 落到 Y:再走 wechat-login 命中 Y
+    r = client.post("/api/v1/auth/wechat-login", json={"code": "c", "device_id": "devR1"})
+    assert r.json()["status"] == "logged_in"
+    assert r.json()["token"]["user"]["id"] == y["id"]
+
+
+def test_rebind_blocked_within_30_days(client, monkeypatch) -> None:
+    """同一手机号 30 天内二次换绑 → 409;占用响应 rebind_available=False。"""
+    phone = "13900139302"
+    _sms_occupy(client, phone)
+    body = _occupy_via_conflict(client, monkeypatch, "openid_rb_302a", phone, "devR2")
+    assert client.post(
+        "/api/v1/auth/wechat/conflict/rebind",
+        json={"conflict_ticket": body["conflict_ticket"], "device_id": "devR2"},
+    ).status_code == 200
+
+    # 第二次:新 openid 撞同号 → 占用响应此时 rebind_available=False
+    body2 = _occupy_via_conflict(client, monkeypatch, "openid_rb_302b", phone, "devR2b")
+    assert body2["rebind_available"] is False
+    assert body2["rebind_blocked_days"] >= 1
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/rebind",
+        json={"conflict_ticket": body2["conflict_ticket"], "device_id": "devR2b"},
+    )
+    assert r.status_code == 409, r.text
+
+
+def test_rebind_expired_ticket_returns_401(client, monkeypatch) -> None:
+    monkeypatch.setattr(security.settings, "WECHAT_BIND_TICKET_EXPIRE_MINUTES", -1)
+    expired = security.create_conflict_ticket(
+        openid="oid", wechat_nickname=None, wechat_avatar_url=None, phone="13900139309"
+    )
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/rebind",
+        json={"conflict_ticket": expired, "device_id": "devR3"},
+    )
+    assert r.status_code == 401, r.text