Collider in RCT Subgroup Analysis

I have ceased to understand what we are discussing in this thread. I thought we were discussing how DAGs could assist in helping us examine whether there is potentially a differential effect of treatment within subgroup and whether there are potential confounders U that would also need adjusting for to identify this. You have written a paper that shows problems with this framework if the subgroup is defined by a pos-randomization variable but most of us were considering pre-randomization subgroups. I understand this comment to mean that you do not believe these DAGs or the resulting adjustment sets are beneficial to find treatment effect heterogeneity? This seems to go against the thesis of this thread. Care to elaborate?