It's really only used by the GUI, but engine states are part of
ARDOUR::Config::extra_xml so this is at least similarly inconsistent.
/* miscellany */
+CONFIG_VARIABLE (bool, try_autostart_engine, "try-autostart-engine,", false)
CONFIG_VARIABLE (std::string, auditioner_output_left, "auditioner-output-left", "default")
CONFIG_VARIABLE (std::string, auditioner_output_right, "auditioner-output-right", "default")
CONFIG_VARIABLE (bool, replicate_missing_region_channels, "replicate-missing-region-channels", false)