chat: harden peg-native tool call parsing (#24329)

* chat: harden peg-native tool call parsing

accept an optional leading type: function field in
build_json_tools_flat_keys so openai style tool calls parse on
templates whose serialization opens on the name field.

return a clean error and log the unparsed fragment on a final peg
parse failure instead of throwing the raw parser position and input.

keep the raw arguments string in func_args_not_string when it is not
valid json instead of aborting the prompt render.

* chat: surface peg-native parse failures

a final peg parse failure threw the raw parser position and input. log
the unparsed fragment and raise a clearer error instead, so a model
output that does not match the expected format no longer fails silently
with an empty assistant turn.

minimal change, no behavior change on successful parses.

* chat: handle openai style tool calls in peg-native

* nits

* common: scope OpenAI wrapper grammar trigger via autoparser flag

* chat: gate type:function parsing leniency on the analysis flag

Thread accept_openai_wrapper from the generator to build_json_tools_flat_keys
so the leading "type": "function" field is accepted only when openai_wrapper_trigger is set.

common/chat.cpp

@@ -2678,8 +2678,10 @@ common_chat_msg common_chat_peg_parse(const common_peg_arena &          src_pars
             }
             return msg;
         }
-        throw std::runtime_error(std::string("Failed to parse input at pos ") + std::to_string(result.end) + ": " +
-                                 effective_input.substr(result.end));
+        LOG_WRN("%s: unparsed %s output: %s\n", __func__, common_chat_format_name(params.format),
+                effective_input.substr(result.end).c_str());
+        throw std::runtime_error(std::string("The model produced output that does not match the expected ") +
+                                 common_chat_format_name(params.format) + " format");
     }
 
     common_chat_msg msg;