fix: preserve file tool toggle for subagents

Maintainer edit: subagents rebuilt their scoped ToolsConfig without carrying tools.file, which re-enabled built-in file tools after the parent agent disabled them. Preserve the file config and add loader/subagent coverage for the disabled path.

tests/test_file_tool_toggle.py

@@ -1,7 +1,21 @@
 from types import SimpleNamespace
 
-from nanobot.config.schema import Config, ToolsConfig
+from nanobot.agent.tools.context import ToolContext
+from nanobot.agent.tools.file_state import FileStates
 from nanobot.agent.tools.filesystem import FileToolsConfig, ReadFileTool
+from nanobot.agent.tools.loader import ToolLoader
+from nanobot.agent.tools.registry import ToolRegistry
+from nanobot.config.schema import Config, ToolsConfig
+
+FILE_TOOL_NAMES = {
+    "apply_patch",
+    "edit_file",
+    "find_files",
+    "grep",
+    "list_dir",
+    "read_file",
+    "write_file",
+}
 
 
 def test_file_tools_enabled_by_default():
@@ -14,3 +28,17 @@ def test_file_tool_gate_follows_flag():
     cfg.file.enable = False
     assert ReadFileTool.enabled(SimpleNamespace(config=cfg)) is False
     assert ReadFileTool.enabled(SimpleNamespace(config=ToolsConfig())) is True
+
+
+def test_file_tool_loader_skips_all_builtin_file_tools_when_disabled(tmp_path):
+    cfg = ToolsConfig(file=FileToolsConfig(enable=False))
+    ctx = ToolContext(
+        config=cfg,
+        workspace=str(tmp_path),
+        file_state_store=FileStates(),
+    )
+    registry = ToolRegistry()
+
+    ToolLoader().load(ctx, registry)
+
+    assert FILE_TOOL_NAMES.isdisjoint(registry.tool_names)