common : gpt-oss handle builtins and unsolicited tool calls

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();

tests/test-chat.cpp

@@ -3077,6 +3077,27 @@ static void test_template_output_peg_parsers(bool detailed_debug) {
             .expect_reasoning("I need to output the invoice details in JSON")
             .expect_content(R"({"amount": 123.45, "date": "2025-12-03"})")
             .run();
+
+
+        // Unsolicited tool calls. There is no good way to handle these, so we return empty content.
+
+        // Builtin function - recipient in role
+        tst.test(
+               "<|channel|>analysis<|message|>I will execute python to say hello<|end|>"
+               "<|start|>assistant to=container.exec<|channel|>commentary<|message|>python3 -c 'print(\"hello\")'")
+            .reasoning_format(COMMON_REASONING_FORMAT_AUTO)
+            .expect_reasoning("I will execute python to say hello")
+            .expect_content("")
+            .run();
+
+        // Builtin function - recipient in channel
+        tst.test(
+               "<|channel|>analysis<|message|>I will execute python to say hello<|end|>"
+               "<|start|>assistant<|channel|>commentary to=python <|constrain|>code<|message|>print(\"hello\")")
+            .reasoning_format(COMMON_REASONING_FORMAT_AUTO)
+            .expect_reasoning("I will execute python to say hello")
+            .expect_content("")
+            .run();
     }
 
     {