fix: scope preserve_thinking to tool-call turns only

chat_template.jinja

@@ -230,7 +230,7 @@
 
     {#- Render reasoning/reasoning_content as thinking channel -#}
     {%- set thinking_text = message.get('reasoning') or message.get('reasoning_content') -%}
-    {%- set thinking_gate = (loop.index0 > ns_turn.last_user_idx) or preserve_thinking -%}
+    {%- set thinking_gate = (loop.index0 > ns_turn.last_user_idx) or (preserve_thinking and message.get('tool_calls')) -%}
     {%- if thinking_text and thinking_gate -%}
         {{- '<|channel>thought\n' + thinking_text + '\n<channel|>' -}}
     {%- endif -%}