diff --git a/app/api/v1/auth.py b/app/api/v1/auth.py
index 9aadae1..0f3ab4c 100644
--- a/app/api/v1/auth.py
+++ b/app/api/v1/auth.py
@@ -13,6 +13,7 @@ from __future__ import annotations
 import logging
 
 from fastapi import APIRouter, HTTPException, Request, status
+from sqlalchemy.exc import IntegrityError
 
 from app.api.deps import CurrentUser, DbSession
 from app.core import test_account
@@ -46,6 +47,8 @@ from app.schemas.auth import (
     WechatBindPhoneJverifyRequest,
     WechatBindPhoneSmsRequest,
     WechatBindResultResponse,
+    WechatConflictContinueRequest,
+    WechatConflictRebindRequest,
     WechatLoginRequest,
     WechatLoginResponse,
 )
@@ -352,6 +355,53 @@ def wechat_bind_phone_jverify(
     )
 
 
+# ===================== 微信占用冲突(M2) =====================
+
+@router.post(
+    "/wechat/conflict/continue",
+    response_model=WechatBindResultResponse,
+    summary="微信占用冲突·继续绑定(登录老账号,能绑就绑)",
+)
+def wechat_conflict_continue(
+    req: WechatConflictContinueRequest, request: Request, db: DbSession
+) -> WechatBindResultResponse:
+    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",
+    )
+
+    user = user_repo.get_user_by_phone(db, claims["phone"])
+    if user is None:
+        # P 期间被腾空(老账号改号/注销)→ 前提已变,让前端重走
+        raise HTTPException(status_code=409, detail="账号状态已变化,请重新登录")
+    if user.status != "active":
+        raise HTTPException(status_code=403, detail="account disabled")
+
+    if user.wechat_openid is None:
+        try:
+            user_repo.attach_wechat_to_user(
+                db, user, openid=claims["openid"],
+                wechat_nickname=claims["wnk"], wechat_avatar_url=claims["wav"],
+            )
+        except IntegrityError:
+            db.rollback()  # openid 被别处绑走 → 只登入不绑
+            user_repo.touch_last_login(db, user)
+    else:
+        user_repo.touch_last_login(db, user)  # X 已绑别的微信 → 只登入,丢弃本次 openid
+
+    completed = onboarding_repo.is_completed(db, user_id=user.id, device_id=req.device_id)
+    logger.info("wechat conflict continue user_id=%d openid=%s***", user.id, 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 e10f529..40ce500 100644
--- a/app/repositories/user.py
+++ b/app/repositories/user.py
@@ -99,6 +99,24 @@ def touch_last_login(db: Session, user: User) -> User:
     return user
 
 
+def attach_wechat_to_user(
+    db: Session, user: User, *, openid: str, wechat_nickname: str | None, wechat_avatar_url: str | None
+) -> 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"。
+    """
+    user.wechat_openid = openid
+    user.wechat_nickname = wechat_nickname
+    user.wechat_avatar_url = wechat_avatar_url
+    user.last_login_at = datetime.now(timezone.utc)
+    db.commit()
+    db.refresh(user)
+    return user
+
+
 def create_wechat_user(
     db: Session,
     *,
diff --git a/tests/test_wechat_conflict.py b/tests/test_wechat_conflict.py
index 81c41fe..c3ead0e 100644
--- a/tests/test_wechat_conflict.py
+++ b/tests/test_wechat_conflict.py
@@ -88,3 +88,66 @@ def test_phone_occupied_returns_conflict_ticket_and_flags(client, monkeypatch) -
     assert body["rebind_available"] is True      # 首次,未换绑过
     assert body["rebind_blocked_days"] == 0
     assert body["occupied_account"]["has_wechat"] is False  # X 是 sms 账号
+
+
+# ===== Task 4: 继续绑定 =====
+
+def test_continue_attaches_wechat_and_logs_into_existing(client, monkeypatch) -> None:
+    """X 无微信 → 继续绑定并入 openid + 登入 X;之后同 openid 登录直接命中 X。"""
+    phone = "13900139201"
+    x_id = _sms_occupy(client, phone)  # X:sms 账号,无微信
+    body = _occupy_via_conflict(client, monkeypatch, "openid_cont_201", phone, "devC1")
+
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/continue",
+        json={"conflict_ticket": body["conflict_ticket"], "device_id": "devC1"},
+    )
+    assert r.status_code == 200, r.text
+    assert r.json()["status"] == "logged_in"
+    assert r.json()["token"]["user"]["id"] == x_id  # 登入的是老账号 X
+
+    # openid 现已并入 X:再走 wechat-login 直接命中 X
+    r = client.post("/api/v1/auth/wechat-login", json={"code": "c", "device_id": "devC1"})
+    assert r.json()["status"] == "logged_in"
+    assert r.json()["token"]["user"]["id"] == x_id
+
+
+def test_continue_when_existing_has_wechat_logs_in_and_discards_openid(client, monkeypatch) -> None:
+    """X 已绑别的微信 → 继续绑定只登入 X、丢弃本次 openid(不覆盖)。"""
+    phone = "13900139202"
+    # 先建一个已绑微信 O1 的账号 X(微信登录 O1 + 短信绑号)
+    monkeypatch.setattr(wxpay, "code_to_userinfo", _fake_userinfo("openid_o1_202"))
+    t = client.post("/api/v1/auth/wechat-login", json={"code": "c", "device_id": "devC2"}).json()["bind_ticket"]
+    x = client.post(
+        "/api/v1/auth/wechat/bind-phone/sms",
+        json={"bind_ticket": t, "phone": phone, "code": "123456", "device_id": "devC2"},
+    ).json()
+    x_id = x["token"]["user"]["id"]
+
+    # 新 openid O2 撞同号 → 占用(has_wechat=True)→ 继续绑定
+    body = _occupy_via_conflict(client, monkeypatch, "openid_o2_202", phone, "devC2b")
+    assert body["occupied_account"]["has_wechat"] is True
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/continue",
+        json={"conflict_ticket": body["conflict_ticket"], "device_id": "devC2b"},
+    )
+    assert r.status_code == 200, r.text
+    assert r.json()["token"]["user"]["id"] == x_id  # 登入 X
+
+    # O2 被丢弃:再走 wechat-login(O2)→ 仍未命中(need_bind_phone)
+    monkeypatch.setattr(wxpay, "code_to_userinfo", _fake_userinfo("openid_o2_202"))
+    assert client.post(
+        "/api/v1/auth/wechat-login", json={"code": "c", "device_id": "devC2b"}
+    ).json()["status"] == "need_bind_phone"
+
+
+def test_continue_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="13900139209"
+    )
+    r = client.post(
+        "/api/v1/auth/wechat/conflict/continue",
+        json={"conflict_ticket": expired, "device_id": "devC3"},
+    )
+    assert r.status_code == 401, r.text