fix(box): tighten sandbox exposure and restore box integration coverage

src/langbot/pkg/provider/tools/loader.py

@@ -2,12 +2,14 @@ from __future__ import annotations
 
 import abc
 import typing
+from typing import TYPE_CHECKING
 
 from langbot_plugin.api.entities.events import pipeline_query
-
-from ...core import app
 import langbot_plugin.api.entities.builtin.resource.tool as resource_tool
 
+if TYPE_CHECKING:
+    from ...core import app
+
 
 preregistered_loaders: list[typing.Type[ToolLoader]] = []
 
@@ -28,9 +30,9 @@ class ToolLoader(abc.ABC):
 
     name: str = None
 
-    ap: app.Application
+    ap: 'app.Application'
 
-    def __init__(self, ap: app.Application):
+    def __init__(self, ap: 'app.Application'):
         self.ap = ap
 
     async def initialize(self):