feat(generation): worker孤儿任务自动恢复 + 429限流结构化提示 (#1677) (#1710)

Co-authored-by: xiaoxia <dev@xiaoxiajianji.com>
Co-committed-by: xiaoxia <dev@xiaoxiajianji.com>

packages/adapters/sqlalchemy_impl/generation_task_repository.py

@@ -138,6 +138,52 @@ class SQLAlchemyGenerationTaskRepository:
             .count()
         )
 
+    def count_running_by_user(self, user_id: str) -> int:
+        """统计指定用户处于 running 状态的任务数（用于限流提示展示）。"""
+        return (
+            self.session.query(GenerationTaskModel)
+            .filter(
+                GenerationTaskModel.created_by_user_id == user_id,
+                GenerationTaskModel.status == GenerationTaskStatus.RUNNING.value,
+            )
+            .count()
+        )
+
+    def count_running_total(self) -> int:
+        """统计全局处于 running 状态的任务数（worker 实际在执行的任务数）。"""
+        return (
+            self.session.query(GenerationTaskModel)
+            .filter(GenerationTaskModel.status == GenerationTaskStatus.RUNNING.value)
+            .count()
+        )
+
+    def estimate_avg_duration_seconds(self, limit: int = 20, default_seconds: float = 120.0) -> float:
+        """估算最近完成任务的平均耗时（秒），用于 429 限流提示的等待预估。
+
+        取最近 N 条 completed 任务的 (completed_at - started_at) 平均值；
+        无足够历史数据时返回 default_seconds。
+        用 Python 侧计算差值，避免 SQLite/PostgreSQL 方言差异。
+        """
+        rows = (
+            self.session.query(GenerationTaskModel.started_at, GenerationTaskModel.completed_at)
+            .filter(
+                GenerationTaskModel.status == GenerationTaskStatus.COMPLETED.value,
+                GenerationTaskModel.started_at.isnot(None),
+                GenerationTaskModel.completed_at.isnot(None),
+            )
+            .order_by(GenerationTaskModel.completed_at.desc())
+            .limit(limit)
+            .all()
+        )
+        durations = [
+            (completed - started).total_seconds()
+            for started, completed in rows
+            if completed and started and (completed - started).total_seconds() > 0
+        ]
+        if not durations:
+            return default_seconds
+        return sum(durations) / len(durations)
+
     def list_recent_by_user(self, user_id: str, limit: int = 5) -> list[GenerationTask]:
         models = (
             self.session.query(GenerationTaskModel)