common : gpt-oss handle builtin and unsolicited tool calls (#21213)

common/chat.cpp

@@ -989,6 +989,10 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
         auto analysis = p.ref("analysis");
         auto preamble = p.rule("preamble", p.literal("<|channel|>commentary<|message|>") + p.content(content) + end);
         auto final_msg = p.rule("final", p.literal("<|channel|>final<|message|>") + p.content(content));
+
+        // Consume any unsolicited tool calls, e.g. builtin functions
+        auto unsolicited = p.rule("unsolicited", p.atomic(p.optional(channel) + p.literal(" to=") + content + end));
+
         auto any = p.rule("any", preamble | analysis);
 
         if (has_response_format) {
@@ -1032,7 +1036,7 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
             return p.zero_or_more(start + any) + start + (tool_call | final_msg);
         }
 
-        return p.zero_or_more(start + any) + start + final_msg;
+        return p.zero_or_more(start + any) + start + (final_msg | unsolicited);
     });
 
     data.parser = parser.save();