diff --git a/app/infrastructure/repositories.py b/app/infrastructure/repositories.py
index 9ffbbf9..352f5c6 100644
--- a/app/infrastructure/repositories.py
+++ b/app/infrastructure/repositories.py
@@ -1864,7 +1864,14 @@ class Database:
         if self._engine is not None:
             async with self._engine.begin() as conn:
                 await conn.run_sync(Base.metadata.create_all)
-        await seed_data(self.session)
+        # 种子容错：个别幂等保护不严的地方(如 demo 用户固定 agent id)可能触发唯一冲突，
+        # 不能让种子失败拖垮 lifespan 建库，否则 app.state.db 未设置→全部 500。
+        try:
+            await seed_data(self.session)
+        except Exception as e:  # noqa: BLE001
+            import logging
+            logging.getLogger("servercore").warning("种子数据写入失败(忽略，应用仍可用): %s", e)
+            await self.session.rollback()
 
     async def close(self) -> None:
         if self._owns_session:
diff --git a/app/infrastructure/seed.py b/app/infrastructure/seed.py
index 9ad2935..19608c1 100644
--- a/app/infrastructure/seed.py
+++ b/app/infrastructure/seed.py
@@ -1045,12 +1045,12 @@ async def _ensure_port_agents(session: AsyncSession, now: str) -> None:
         if (user_id, port) in seen:
             continue
         seen.add((user_id, port))
-        existing = await session.scalar(
-            select(Agent.id).where(Agent.user_id == user_id, Agent.port == port).limit(1)
+        existing_ids = set(
+            (await session.execute(select(Agent.id).where(Agent.user_id == user_id, Agent.port == port))).scalars()
         )
-        if existing is not None:
-            continue
         for seed in AGENT_SEED:
+            if seed["id"] in existing_ids:
+                continue  # 已存在，跳过（幂等，避免 (id,user_id,port) 唯一冲突）
             session.add(
                 Agent(
                     id=seed["id"], user_id=user_id, port=port, name=seed["name"],