diff --git a/hermes_cli/cli_model_switch_mixin.py b/hermes_cli/cli_model_switch_mixin.py
index 3bf94e06f4..d84cdc073b 100644
--- a/hermes_cli/cli_model_switch_mixin.py
+++ b/hermes_cli/cli_model_switch_mixin.py
@@ -517,6 +517,7 @@ class CLIModelSwitchMixin:
     def _snapshot_model_runtime(self) -> dict:
         """Capture current CLI and agent model runtime for one-turn restore."""
         agent = getattr(self, "agent", None)
+        # ``reasoning_config`` is a mutable dict: deepcopy it so a later in-place edit cannot alias the snapshot.
         return {
             **_runtime_fields(self),
             "reasoning_config": copy.deepcopy(getattr(self, "reasoning_config", None)),