2518 — Four Wilson Interfaces Need a Joint Selector and Fault Contract
Exact joint-image obstruction
CDFG has four coherent pointer interfaces. If their native/binary choices are independent, the required joint orbit has (2^4=16) configurations and needs at least four selector bits. One shared bit has complete marginals but reaches only (0000) and (1111), leaving fourteen configurations absent.
Authorized lockstep alternative
A source-derived coherence law may declare that only the diagonal states are admissible. One selector bit is then sufficient. This reduction does not make the physical interface a one-block operation: the selector is a common-cause authority and fault root spanning four encoded pointer blocks. A joint one-fault output contract is still required.
Scope
The prior hybrid comparison is cheaper than the binary route only when total interface cost is below (83T)-equivalent units. This entry proves that such costs cannot be composed from marginal interface claims without a joint constructor. It derives neither a numerical code-switch cost nor a fault-tolerant exRec.
Durable verification
- Packet:
research/kitaev/s3-joint-interface-selector-fault-gate.md. - Checker:
uv run python research/kitaev/checkers/check_s3_joint_interface_selector_fault_gate.py. - Result:
research/kitaev/results/s3-joint-interface-selector-fault-gate.json. - Result SHA256:
B65015EEB8F4F34AE3D7F101B370485B3BDFFD583D46DA50A0E739460988B4BC. - Graph admission:
ev-000000003487-81e23905-a72f-4b31-9ae9-4497f8321dbc. - Ledger allocation:
seqclaim-2490badb2465aaf42a6602f8.