Composition constraint: LoungeMixin requires WarrenMemberMixin on
the chain (it reads/writes the back-ref via getWarren). The TS
bound documents it; this runtime check enforces it the first time
an instance registers (mirrors GlobbableMixin's opt-in).
Declared-warren seed. Consumed once by Phase 2 of the Hydrator — an instruction field, not a stored property (no paired getter; the live affiliation is
WarrenMember.getWarren()).