I am proposing here a fix to keep working with the current sim structures to have RDO identifiers after full digi being usable for reco. This way we can keep using the produced HITS files and keep working in R21, while it should be cleaned up in master.
I ran on 500 single muons to check if the chi2 I get from the extension look good (so the HGTD_Cluster are in the right position after retrieving the RDOs), and that worked fine as far as I can tell. More in depth validation is still needed.
In addition, I am adding a couple of fixes to have everything running (similar to what was in MR 46526.
Tagging @tadej @ncalace @nstyles @cohm @dshope for feedback.