When using geometries coming from externally-generated (using standalone GeoModel) SQLite files, we cannot rely on the Sensitive Detector volumes having their copy number correctly set to a valid SiHitIdentifier, as we do when running the Geometry building fully within Athena.
Instead, we use the name of the GeoFullPhysVol to contain and later extract the necessary indices for building an Identifier when creating the HITS.
This relies on updates to GeoModel in GeoModelDev/GeoModel!181 (merged) in order for the names to be written properly, this is not used in any production workflow, so does not need to wait for those developments to be merged and picked up in Athena via an update of the GeoModel tag.
This approach can be extended to other systems using GeoModelXml, such as the HGTD (FYI @dshope @aleopold @sridouan)
Adding also @boudreau @dellacqu @tsulaia @rbianchi @jmasik @sroe @hhayward for info.