Composite-System Corridor: Independent Ledger Composition, Tensor-Class Product, and the Entanglement Slot

This paper extends the Forced Sequence / Corridor program to composite systems. After deriving the Born slot, local linear norm-preserving closed evolution (Schrodinger-class slot), and interface-cut conditioning (collapse-class slot), the next forced step is composition: how two subsystem ledgers combine without introducing forbidden tie-break structure. The paper shows that subsystem superposition compatibility, composite superposition closure over product generators, and Born-consistent factorization on product states force a tensor-class product slot for the composite carrier. This yields an entanglement slot: composite summaries need not factor into a single product, and non-factorability is the corridor definition of entanglement. The paper also derives the corridor form of local conditioning in composites: a local outcome registration updates the joint ledger by normalized filtering, changing conditional predictions for the other subsystem as bookkeeping rather than superluminal dynamics. Open-system reductions, density-matrix style bookkeeping, and interaction-generator selection are deferred to the next forced corridors.