Make <|constrain|> optional

Author: aldehir

common/parsers/harmony.cpp

@@ -63,7 +63,7 @@ void harmony_msg_parser::commentary() {
 
 void harmony_msg_parser::user_function() {
     static const common_regex tool_call_regex(
-        "functions\\.([a-zA-Z_][a-zA-Z0-9_]*)\\s*(<\\|constrain\\|>([a-z]+))?<\\|message\\|>"
+        "functions\\.([a-zA-Z_][a-zA-Z0-9_]*)\\s*(<\\|constrain\\|>)?([a-z]+)<\\|message\\|>"
     );
     if (auto res = builder.try_consume_regex(tool_call_regex)) {
         auto name = builder.str(res->groups[1]);