(following discussion with Sophie on Weds, added myself as a reviewer) - this ticket looks great, adding nice gen3 functionality to SSI processing. I only have 1 minor comment on the pipe_tasks PR regarding the WCS pixel scale offset factor, and whether or not this factor should be configurable. If you think a factor of 2 will always be sufficient to catch this issue, then that looks fine to me, with no extra code required.
I think some amount (most?) of the obs_subaru code was already merged to master previously, so I haven't looked at that specifically here. However, as noted above, I have been using the pipeline on this ticket branch without issue, and the outputs look good to me. I note that ticket branch
DM-31491 in obs_subaru still has some additional differences to master in the pipelines/DRPFakes.yaml pipeline - should this also be in a PR?
Otherwise, this looks great. Assuming Jenkins doesn't complain, then this should be good to merge. Nicely done.