Based on what you're doing, I think this is going to break here:
https://github.com/tjwebb/xtuple/blob/c113689b222cc2531d59396ec5e5fb17928b599e/lib/orm/source/xt/javascript/schema.sql#L366
https://github.com/tjwebb/xtuple/blob/c113689b222cc2531d59396ec5e5fb17928b599e/lib/orm/source/xt/javascript/schema.sql#L454
https://github.com/tjwebb/xtuple/blob/c113689b222cc2531d59396ec5e5fb17928b599e/lib/orm/source/xt/javascript/schema.sql#L470

XT.Schema.columnInfo(schemaTable, columns); will not know about your function column.