Continue PR #207 from 45b3d9b2625dcf7695a7fbc811e3e2678af6fb27. The height-kernel assignment is complete; do not minimize variance. Consume Fable's prefix-exchange construction from PR #208 at 3d8aa03034d5207cdab3129eb78534c0f77d2384 without changing its files.
Check the coordinator's direct-dual and variance-procedure deductions. Then test one explicit estimate for the capacity of the true integer prefix exchanges. Establish a substantive estimate or an exact counterexample, retaining zero-real-mass destinations and all prefix capacities. State precisely the prime-mass information used and the unproved estimate needed for a scalable family.
Ownership: new notes, checks and outputs here, one focused test, and regenerated CONTEXT.md. No greedy search, optimal-basis search, larger-N computation, general audit or variance optimization. Fable owns the construction; this continuation owns its analytic capacity conditions. Use one numerical thread. Commit and push to #207, leaving it open.