修改了nanobot，往Hermes agent的风格走，进度1/3

app-instance/backend/beaver/engine/__init__.py

@@ -0,0 +1,31 @@
+"""Unified Beaver agent engine.
+
+这里不做顶层 eager import，避免子模块导入时触发循环依赖。
+对外仍然保留同样的导出名称，但改成按需加载。
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+__all__ = ["AgentLoop", "AgentProfile", "AgentRunResult", "EngineLoader", "EngineLoadResult"]
+
+
+def __getattr__(name: str) -> Any:
+    if name == "EngineLoader":
+        from .loader import EngineLoader
+
+        return EngineLoader
+    if name == "EngineLoadResult":
+        from .loader import EngineLoadResult
+
+        return EngineLoadResult
+    if name in {"AgentLoop", "AgentProfile", "AgentRunResult"}:
+        from .loop import AgentLoop, AgentProfile, AgentRunResult
+
+        return {
+            "AgentLoop": AgentLoop,
+            "AgentProfile": AgentProfile,
+            "AgentRunResult": AgentRunResult,
+        }[name]
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")