diff --git a/modules/usage_tracker.py b/modules/usage_tracker.py
index 14a2770..a1f8c60 100644
--- a/modules/usage_tracker.py
+++ b/modules/usage_tracker.py
@@ -90,35 +90,58 @@ class UsageTracker:
             return QUOTA_DEFAULTS["search_daily"]
         return QUOTA_DEFAULTS["default"][metric]
 
-    def _ensure_window(self, metric: QuotaKey) -> Tuple[int, Optional[str], datetime, datetime]:
+    def _ensure_window(
+        self,
+        metric: QuotaKey,
+        init_if_missing: bool = False,
+    ) -> Tuple[int, Optional[str], Optional[datetime], Optional[datetime]]:
         """Returns tuple(count, window_start_iso, window_start_dt, reset_at_dt)."""
         config = self._get_quota_config(metric)
         window_hours = config["window_hours"]
         window_delta = timedelta(hours=window_hours)
         window_data = self._state["windows"].setdefault(metric, {"count": 0, "window_start": None})
+        count = int(window_data.get("count", 0))
         window_start_iso = window_data.get("window_start")
         now = datetime.utcnow()
+        window_start_dt: Optional[datetime] = None
 
         if window_start_iso:
             try:
                 parsed = datetime.fromisoformat(window_start_iso.replace("Z", ""))
                 window_start_dt = floor_to_hour(parsed)
             except ValueError:
-                window_start_dt = floor_to_hour(now)
-        else:
-            window_start_dt = floor_to_hour(now)
-            window_data["window_start"] = frame_iso(window_start_dt)
+                window_start_dt = None
 
-        reset_at_dt = window_start_dt + window_delta
-        if now >= reset_at_dt and window_data.get("window_start"):
-            window_data["count"] = 0
-            window_start_dt = floor_to_hour(now)
+        reset_at_dt: Optional[datetime] = None
+        if window_start_dt:
             reset_at_dt = window_start_dt + window_delta
+            if now >= reset_at_dt:
+                window_data["count"] = 0
+                count = 0
+                if init_if_missing:
+                    window_start_dt = floor_to_hour(now)
+                    window_data["window_start"] = frame_iso(window_start_dt)
+                    reset_at_dt = window_start_dt + window_delta
+                else:
+                    window_start_dt = None
+                    window_data["window_start"] = None
+                    reset_at_dt = None
+
+        if window_start_dt is None and init_if_missing:
+            window_start_dt = floor_to_hour(now)
             window_data["window_start"] = frame_iso(window_start_dt)
+            reset_at_dt = window_start_dt + window_delta
+        elif count == 0 and window_data.get("window_start") and not init_if_missing:
+            # 没有真实用量时清理遗留的窗口起点，使下一次调用时重新计窗。
+            window_data["window_start"] = None
+            window_start_iso = None
+
+        if window_start_dt and not reset_at_dt:
+            reset_at_dt = window_start_dt + window_delta
 
         return (
-            int(window_data.get("count", 0)),
-            window_data["window_start"],
+            count,
+            window_data.get("window_start"),
             window_start_dt,
             reset_at_dt,
         )
@@ -126,7 +149,9 @@ class UsageTracker:
     def check_and_increment(self, metric: QuotaKey) -> Tuple[bool, Dict[str, str]]:
         """Check quota and increment if allowed. Returns (allowed, info)."""
         with self._lock:
-            count, window_start_iso, window_start_dt, reset_at_dt = self._ensure_window(metric)
+            count, window_start_iso, window_start_dt, reset_at_dt = self._ensure_window(
+                metric, init_if_missing=True
+            )
             quota = self._get_quota_config(metric)["limit"]
             if count >= quota:
                 reset_at_iso = frame_iso(reset_at_dt)
@@ -139,8 +164,6 @@ class UsageTracker:
 
             new_count = count + 1
             self._state["windows"][metric]["count"] = new_count
-            if not window_start_iso:
-                self._state["windows"][metric]["window_start"] = frame_iso(window_start_dt)
             self._state["updated_at"] = self._now_iso()
             self._save()