LogMessageFormat: Only relevant when action is `LOG`. Defines the message to log when the breakpoint hits. The message may include parameter placeholders `$0`, `$1`, etc. These placeholders are replaced with the evaluated value of the appropriate expression. Expressions not referenced in `log_message_format` are not logged. Example: `Message received, id = $0, count = $1` with `expressions` = `[ message.id, message.count ]`.