修改了nanobot，往Hermes agent的风格走，进度1/3

app-instance/backend/beaver/engine/session/manager.py

@@ -0,0 +1,143 @@
+"""Beaver session 子系统对 runtime 暴露的统一门面。"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any
+
+from .models import MessageRecord
+from .search import SessionSearchService
+from .store import SessionStore
+
+
+class SessionManager:
+    """供 AgentLoop / services / MCP tools 使用的统一 session facade。"""
+
+    def __init__(self, workspace: str | Path, db_path: str | Path | None = None) -> None:
+        self.workspace = Path(workspace)
+        self.sessions_dir = self.workspace / "sessions"
+        self.sessions_dir.mkdir(parents=True, exist_ok=True)
+        self.db_path = Path(db_path) if db_path is not None else self.sessions_dir / "state.db"
+        self.store = SessionStore(self.db_path)
+        self.search = SessionSearchService(self.store)
+
+    def close(self) -> None:
+        self.store.close()
+
+    def ensure_session(
+        self,
+        session_id: str,
+        *,
+        source: str = "unknown",
+        model: str | None = None,
+        title: str | None = None,
+        user_id: str | None = None,
+        parent_session_id: str | None = None,
+    ) -> str:
+        return self.store.ensure_session(
+            session_id,
+            source=source,
+            model=model,
+            title=title,
+            user_id=user_id,
+            parent_session_id=parent_session_id,
+        )
+
+    def get_session(self, session_id: str) -> dict[str, Any] | None:
+        record = self.store.get_session_record(session_id)
+        return record.to_dict() if record is not None else None
+
+    def get_or_create(
+        self,
+        session_id: str,
+        *,
+        source: str = "unknown",
+        model: str | None = None,
+        title: str | None = None,
+        user_id: str | None = None,
+        parent_session_id: str | None = None,
+    ) -> dict[str, Any]:
+        self.ensure_session(
+            session_id,
+            source=source,
+            model=model,
+            title=title,
+            user_id=user_id,
+            parent_session_id=parent_session_id,
+        )
+        session = self.get_session(session_id)
+        if session is None:
+            raise RuntimeError(f"Failed to create session {session_id!r}")
+        return session
+
+    def append_message(self, session_id: str, **kwargs: Any) -> int:
+        return self.store.append_message(session_id, **kwargs)
+
+    def get_event_records(self, session_id: str) -> list[MessageRecord]:
+        """返回当前 session 的完整事件流。
+
+        这里和 `get_messages_as_conversation()` 的区别很关键：
+        - `get_event_records()` 面向 runtime / replay / audit，保留隐藏系统事件
+        - `get_messages_as_conversation()` 面向 prompt builder，只暴露可进上下文的事件
+
+        第 6 阶段开始后，session 已不再只是“聊天消息存储”，而是在逐步收敛成
+        “外部事件流 + 上层投影视图”。
+        """
+
+        return self.store.get_event_records(session_id)
+
+    def get_run_event_records(self, session_id: str, run_id: str) -> list[MessageRecord]:
+        """返回某一次 direct run / future bus run 对应的事件片段。"""
+
+        return self.store.get_run_event_records(session_id, run_id)
+
+    def list_run_ids(self, session_id: str) -> list[str]:
+        """按出现顺序列出当前 session 的所有 run_id。"""
+
+        return self.store.list_run_ids(session_id)
+
+    def get_messages_as_conversation(self, session_id: str) -> list[dict[str, Any]]:
+        return self.store.get_messages_as_conversation(session_id)
+
+    def get_visible_history(self, session_id: str, max_messages: int = 500) -> list[dict[str, Any]]:
+        """返回适合注入 prompt 的可见历史切片。
+
+        这里故意不直接暴露完整事件流，而是继续提供“模型可消费历史”这个投影视图：
+        1. 只包含 `context_visible=True` 的事件
+        2. 继续保留旧式窗口裁剪逻辑，避免当前主链行为突然变化
+        3. 让 `ContextBuilder` 明确消费的是“上游裁剪后的可见片段”
+        """
+
+        history = self.get_messages_as_conversation(session_id)
+        sliced = history[-max_messages:]
+        for index, message in enumerate(sliced):
+            if message.get("role") == "user":
+                sliced = sliced[index:]
+                break
+        return sliced
+
+    def get_history(self, session_id: str, max_messages: int = 500) -> list[dict[str, Any]]:
+        """兼容旧名称，实际返回可见历史切片。"""
+
+        return self.get_visible_history(session_id, max_messages=max_messages)
+
+    def update_system_prompt(self, session_id: str, system_prompt: str) -> None:
+        self.store.update_system_prompt(session_id, system_prompt)
+
+    def update_usage(self, session_id: str, **kwargs: Any) -> None:
+        self.store.update_usage(session_id, **kwargs)
+
+    def end_session(self, session_id: str, end_reason: str) -> None:
+        self.store.end_session(session_id, end_reason)
+
+    def reopen_session(self, session_id: str) -> None:
+        self.store.reopen_session(session_id)
+
+    def list_sessions_rich(self, **kwargs: Any) -> list[dict[str, Any]]:
+        return self.search.list_sessions_rich(**kwargs)
+
+    def search_messages(self, **kwargs: Any) -> list[dict[str, Any]]:
+        return self.search.search_messages(**kwargs)
+
+    def resolve_session_id(self, session_id_or_prefix: str) -> str | None:
+        return self.search.resolve_session_id(session_id_or_prefix)