Why: U0 (merged in RDM) rules that domain logic stays downstream and the base needs seven minimal generic capabilities; the formal four-element applications are the only legal path to base changes.
Evidence: All current-state citations re-verified at Dev 34a2bbe (backend fe7c245); RDM requirement source pinned at RDM main ca72cfc.
Impact: New proposal doc + one INDEX row; no code, no surface change in this PR.
Refs: RDM U0 proposal section 5 / ruling D1; extension-compat-policy; phase-plan section 3.3.