diff --git a/src/ai_client.py b/src/ai_client.py
index 0db21274..83603196 100644
--- a/src/ai_client.py
+++ b/src/ai_client.py
@@ -524,7 +524,12 @@ def _set_tool_preset_result(preset_name: Optional[str]) -> Result[None]:
  capturing the original exception. The legacy caller (set_tool_preset)
  calls this helper for the load step; on Result errors, the caller still
  completes (state remains partially-set; the cache invalidation runs).
+
+ IMPORTANT: This function MODIFIES module-level globals (_active_tool_preset,
+ _tool_approval_modes, _agent_tools). Without 'global' declarations, the
+ assignments would create local variables that are discarded on return.
  """
+ global _active_tool_preset, _tool_approval_modes, _agent_tools
  if not preset_name or preset_name == "None":
   return Result(data=None)
  try: