Hi @Asterix ,
Probably you might be able to achieve this with a xml business rule with the usage of validation xml, and valid if found outputs. In this case, in your validation xml you can simply add a hierarchy select query to check the matching candidates with the given constraints( skill and product skill and availability). If this returns at least one row, then you can set valid_if_found output property to ‘Y’. Finally in the xml output you can have the same validation query and through the xpath, you can assign the first candidate(technician) on the filtered list.
Also you can try out a client script to assign the technician to check the constraints and then set the matching technician on the field.
BR,
SAAALK