Per DM with ebellm, our source count metrics should be agnostic to whether or not we are running fakes processing. However, the pipeline does not distinguish between fake and natural sources; even ProcessCcdWithFakesTask forgets this information as soon as it modifies the image. There is a FAKE mask plane and corresponding catalog flags, but these flags are not suitable for source filtering.
The current best way to identify fake sources is to cross-match them to the original fakes catalog, as is done for the existing fakes metrics. This is adds a dependency on a dataset that does not exist in non-fakes pipelines, though this can be turned on and off in pipeline configurations at the ap_verify level. Add support for such cross-matching to the existing metrics, preferably in a way that leaves the Diffim and SFP metrics portable across pipelines.