diff --git a/backend/routes/garmin.py b/backend/routes/garmin.py
index 0800413..2afa248 100644
--- a/backend/routes/garmin.py
+++ b/backend/routes/garmin.py
@@ -115,7 +115,18 @@ def login():
     if not garmin_email:
         return jsonify({"error": "缺少 Garmin 邮箱"}), 400
 
-    session_id = garmin_auth.start_login(g.user_id, garmin_email, password)
+    try:
+        session_id = garmin_auth.start_login(
+            g.user_id, garmin_email, password, force=bool(data.get("force"))
+        )
+    except garmin_auth.LoginRateLimited as e:
+        # 429, not 400: the request was well-formed and the client should
+        # retry later — and the body says when, and why not now.
+        return jsonify({
+            "error": str(e),
+            "status": "rate_limited",
+            "retryAfterSeconds": garmin_auth.retry_after_seconds(g.user_id),
+        }), 429
     return jsonify({"session": session_id, "status": "starting"}), 202
 
 
diff --git a/backend/services/garmin_auth.py b/backend/services/garmin_auth.py
index 07a8078..7a09cc6 100644
--- a/backend/services/garmin_auth.py
+++ b/backend/services/garmin_auth.py
@@ -129,8 +129,47 @@ def _run_login(session_id, user_id, garmin_email, password, is_cn, import_garmin
         _set(session_id, "failed", error=error, code=None)
 
 
-def start_login(user_id, garmin_email, password, import_garmin=None, is_cn=None):
-    """Kick off a login in the background. Returns the session id."""
+class LoginRateLimited(Exception):
+    """Refused before contacting Garmin, because a login 429 is still active."""
+
+
+def retry_after_seconds(user_id):
+    """Seconds until the login cooldown lapses, or None."""
+    blocked = garmin_svc.sso_cooldown(user_id)
+    if not blocked:
+        return None
+    return max(0, int((blocked - datetime.datetime.utcnow()).total_seconds()))
+
+
+def start_login(user_id, garmin_email, password, import_garmin=None,
+                is_cn=None, force=False):
+    """Kick off a login in the background. Returns the session id.
+
+    Refuses while a login 429 is still in its window. Re-binding is the
+    obvious thing to try when syncing is blocked — "just get a fresh token" —
+    but it goes through `garth.login()`, which is the *same* SSO endpoint that
+    is doing the blocking, by a heavier path than the token refresh. The limit
+    is keyed to the account, so a new password entry, a new device or a new
+    network reaches the same wall, and each attempt pushes the window out.
+
+    `force` overrules the recorded deadline, which is this app's own 24h guess
+    rather than anything Garmin stated.
+    """
+    if force:
+        garmin_svc.clear_rate_limit(user_id)
+    else:
+        blocked = garmin_svc.sso_cooldown(user_id)
+        if blocked:
+            minutes = int(
+                (blocked - datetime.datetime.utcnow()).total_seconds() // 60
+            )
+            raise LoginRateLimited(
+                "Garmin 正在限制该账号的登录请求。重新绑定走的是同一个登录接口，"
+                f"现在重试只会延长封锁。预计 {blocked.isoformat(timespec='minutes')} "
+                f"UTC 之后恢复（约 {minutes} 分钟）。"
+                "限流按账号计算，换设备或换网络都绕不开。"
+            )
+
     _cleanup(user_id)
 
     session_id = str(uuid.uuid4())
diff --git a/backend/tests/test_garmin_mfa.py b/backend/tests/test_garmin_mfa.py
index e2a9017..2a21a40 100644
--- a/backend/tests/test_garmin_mfa.py
+++ b/backend/tests/test_garmin_mfa.py
@@ -276,3 +276,52 @@ class TestEndpoints:
         assert wait_status(sid, "done", "failed") == "done"
         assert client.get("/api/garmin/auth-status", headers=auth).get_json()[
             "hasToken"] is True
+
+
+class TestRebindingIsGatedToo:
+    """"Just re-enter the password and get a fresh token" is the obvious thing
+    to try when syncing is blocked — and it is the worst thing to try.
+
+    `garth.login()` is the same SSO endpoint that is doing the blocking, by a
+    heavier path than the token refresh, and the limit is keyed to the account
+    so a new device or network reaches the same wall.
+    """
+
+    def test_login_is_refused_inside_the_window(self, db, user):
+        garmin_svc._note_rate_limit(user["id"], "sso")
+        with pytest.raises(garmin_auth.LoginRateLimited):
+            garmin_auth.start_login(user["id"], "a@example.com", "pw")
+
+    def test_no_session_row_is_created_by_a_refusal(self, db, user):
+        garmin_svc._note_rate_limit(user["id"], "sso")
+        with pytest.raises(garmin_auth.LoginRateLimited):
+            garmin_auth.start_login(user["id"], "a@example.com", "pw")
+        rows = db.query_all(
+            "SELECT id FROM garmin_mfa_sessions WHERE user_id = ?", [user["id"]])
+        assert rows == []
+
+    def test_a_data_429_does_not_block_rebinding(self, db, user, monkeypatch):
+        started = []
+        monkeypatch.setattr(garmin_auth.threading, "Thread",
+                            lambda **kw: type("T", (), {"start": lambda s: started.append(1)})())
+        garmin_svc._note_rate_limit(user["id"], "data")
+        garmin_auth.start_login(user["id"], "a@example.com", "pw")
+        assert started == [1]
+
+    def test_force_overrules_the_estimate(self, db, user, monkeypatch):
+        started = []
+        monkeypatch.setattr(garmin_auth.threading, "Thread",
+                            lambda **kw: type("T", (), {"start": lambda s: started.append(1)})())
+        garmin_svc._note_rate_limit(user["id"], "sso")
+        garmin_auth.start_login(user["id"], "a@example.com", "pw", force=True)
+        assert started == [1]
+
+    def test_the_endpoint_answers_429_with_a_retry_hint(self, client, auth, db, user):
+        garmin_svc._note_rate_limit(user["id"], "sso")
+        resp = client.post("/api/garmin/login",
+                           json={"garminPassword": "pw", "garminEmail": "a@example.com"},
+                           headers=auth)
+        assert resp.status_code == 429
+        body = resp.get_json()
+        assert body["retryAfterSeconds"] > 0
+        assert "延长封锁" in body["error"]
diff --git a/client/src/pages/DataSync.css b/client/src/pages/DataSync.css
index 63e9855..a8dec57 100644
--- a/client/src/pages/DataSync.css
+++ b/client/src/pages/DataSync.css
@@ -322,3 +322,23 @@
 .sync-records-link:active {
   background: var(--surface-0);
 }
+
+/* Shown only after the cooldown refused a sync. Deliberately plain and set
+   apart from the primary actions: it exists as a way out of a wrong estimate,
+   not as a second 同步 button — pressing it inside Garmin's real window is
+   what extends the lockout. */
+.sync-force {
+  display: block;
+  width: auto;
+  margin-top: 0.6rem;
+  padding: 0.4rem 0.8rem;
+  font-size: 0.78rem;
+  font-weight: 600;
+  color: var(--text-secondary);
+  background: var(--surface-1);
+  border: 1px solid var(--border-strong);
+  border-radius: 999px;
+  cursor: pointer;
+}
+
+.sync-force:disabled { color: var(--text-muted); cursor: default; }
diff --git a/client/src/pages/SyncPage.tsx b/client/src/pages/SyncPage.tsx
index d8860b6..d5f5b6b 100644
--- a/client/src/pages/SyncPage.tsx
+++ b/client/src/pages/SyncPage.tsx
@@ -54,6 +54,10 @@ function SyncPage() {
 
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState('');
+  /* Whether the last attempt was refused by the recorded cooldown. Gates the
+     强制重试 button: offering it unconditionally would invite the very thing
+     the cooldown prevents. */
+  const [blocked, setBlocked] = useState(false);
   const [message, setMessage] = useState('');
 
   const pollRef = useRef<number | null>(null);
@@ -233,20 +237,26 @@ function SyncPage() {
     }).open();
   };
 
-  /** The one manual sync: the chosen range, in the background, with progress. */
-  const syncHistory = async () => {
+  /** The one manual sync: the chosen range, in the background, with progress.
+   *
+   *  `force` discards the recorded cooldown first. Offered only after a
+   *  refusal, and never as the default: the cooldown exists because trying
+   *  again inside Garmin's login window is what extends it. */
+  const syncHistory = async (force?: boolean) => {
     setError('');
     setMessage('');
+    setBlocked(false);
     setLoading(true);
     try {
       // 0 means "everything" and -1 "since the last sync"; the backend caps
       // the former at what Garmin will actually serve.
-      const started = await apiClient.syncGarminData(range);
+      const started = await apiClient.syncGarminData(range, undefined, force);
       const s = await refresh();
       // A refused start (Garmin is throttling us) used to be swallowed: the
       // button did nothing, no progress bar appeared, and no reason was shown.
       if (started.status === 'rate_limited' || s?.status === 'rate_limited') {
         setError(started.message || s?.lastError || 'Garmin 正在限流，稍后会自动恢复。');
+        setBlocked(true);
         return;
       }
       beginSyncPolling();
@@ -311,7 +321,20 @@ function SyncPage() {
 
   return (
     <Screen title="数据同步" backLink>
-      {error && <div className="screen-error">{error}</div>}
+      {error && (
+        <div className="screen-error">
+          {error}
+          {blocked && (
+            <button
+              className="sync-force"
+              onClick={() => syncHistory(true)}
+              disabled={loading}
+            >
+              我确认已恢复，强制重试
+            </button>
+          )}
+        </div>
+      )}
       {message && <div className="screen-ok">{message}</div>}
 
       {/* Step 1 — link the Garmin account, once. */}
@@ -445,7 +468,10 @@ function SyncPage() {
 
               <button
                 className="btn btn-primary btn-large sync-primary"
-                onClick={syncHistory}
+                /* Wrapped, not passed directly: React hands the handler a
+                   MouseEvent, which as `force` is truthy — every ordinary
+                   sync would then bypass the cooldown. */
+                onClick={() => syncHistory()}
                 disabled={busy}
               >
                 {loading ? '正在启动…' : '开始同步'}
diff --git a/client/src/services/api.ts b/client/src/services/api.ts
index 9f6d9fd..958d008 100644
--- a/client/src/services/api.ts
+++ b/client/src/services/api.ts
@@ -613,13 +613,21 @@ class ApiClient {
    * plaintext password must be supplied because only a hash is kept — and an
    * MFA-protected account cannot log in this way at all (see garmin_login.py).
    */
-  /** Starts a sync in the background; poll getGarminSyncStatus for progress. */
-  async syncGarminData(days?: number, garminPassword?: string) {
+  /**
+   * Starts a sync in the background; poll getGarminSyncStatus for progress.
+   *
+   * `force` discards the recorded rate-limit cooldown before trying. That
+   * deadline is the app's own 24h guess, not something Garmin stated, so the
+   * user must be able to overrule it — but only deliberately: attempting a
+   * login inside Garmin's real window extends the window.
+   */
+  async syncGarminData(days?: number, garminPassword?: string, force?: boolean) {
     const { data } = await this.client.post<{
       status: string; days?: number; message?: string; retryAfterSeconds?: number;
     }>(
       '/garmin/sync',
       {
+        ...(force ? { force: true } : {}),
         // `days` must survive being 0 — that is "全部历史", not "unset".
         // `days ? …` dropped it, so the backend fell back to its 7-day
         // default and a full backfill silently pulled a week.