fix(agent): bound per-session file state

nanobot/agent/loop.py

@@ -76,6 +76,7 @@ from nanobot.session.goal_state import (
 from nanobot.session.history_visibility import HIDDEN_HISTORY_META
 from nanobot.session.keys import UNIFIED_SESSION_KEY, remember_last_channel
 from nanobot.session.manager import (
+    SESSION_CACHE_MAX_SIZE,
     Session,
     SessionManager,
     replay_max_messages_for_context,
@@ -380,7 +381,7 @@ class AgentLoop:
         self.tools = tool_registry if tool_registry is not None else ToolRegistry()
         # One file-read/write tracker per logical session. The tool registry is
         # shared by this loop, so tools resolve the active state via contextvars.
-        self._file_state_store = FileStateStore()
+        self._file_state_store = FileStateStore(max_sessions=SESSION_CACHE_MAX_SIZE)
         self._exec_session_manager = ExecSessionManager()
         self.runner = AgentRunner()
         self.subagents = SubagentManager(
@@ -818,8 +819,13 @@ class AgentLoop:
             self.sessions.invalidate(key)
             await self._cancel_active_tasks(key)
         finally:
+            self.discard_session_file_state(key)
             self._discarding_sessions.discard(key)
 
+    def discard_session_file_state(self, key: str) -> None:
+        """Forget ephemeral file-read state for a reset or removed session."""
+        self._file_state_store.discard(key)
+
     def _effective_session_key(self, msg: InboundMessage) -> str:
         """Return the session key used for task routing and mid-turn injections."""
         if self._unified_session and not msg.session_key_override:

nanobot/agent/tools/file_state.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import hashlib
 import os
+from collections import OrderedDict
 from contextvars import ContextVar, Token
 from dataclasses import dataclass
 from pathlib import Path
@@ -135,21 +136,30 @@ class FileStates:
 
 
 class FileStateStore:
-    """Lookup table for per-session file read/write state."""
+    """Bounded lookup table for per-session file read/write state."""
 
-    __slots__ = ("_states_by_key",)
+    __slots__ = ("_max_sessions", "_states_by_key")
 
-    def __init__(self) -> None:
-        self._states_by_key: dict[str, FileStates] = {}
+    def __init__(self, *, max_sessions: int = 128) -> None:
+        if max_sessions <= 0:
+            raise ValueError("max_sessions must be positive")
+        self._max_sessions = max_sessions
+        self._states_by_key: OrderedDict[str, FileStates] = OrderedDict()
 
     def for_session(self, session_key: str | None) -> FileStates:
         key = session_key or "__default__"
-        states = self._states_by_key.get(key)
+        states = self._states_by_key.pop(key, None)
         if states is None:
             states = FileStates()
-            self._states_by_key[key] = states
+        self._states_by_key[key] = states
+        while len(self._states_by_key) > self._max_sessions:
+            self._states_by_key.popitem(last=False)
         return states
 
+    def discard(self, session_key: str | None) -> None:
+        """Forget file state when a session is reset or removed."""
+        self._states_by_key.pop(session_key or "__default__", None)
+
     def clear(self) -> None:
         self._states_by_key.clear()