This paper establishes a sharp phase boundary for forced-prefix feasibility in the accelerated Collatz lift geometry under the rounded-critical regime a=round (p∗m), p∗=1log23. a = round (p^* m), p^* = 1₂ 3. a=round (p∗m), p∗=log231. We prove that the first infeasible prefix depth r∗r^*r∗ satisfies r∗m→2 (1−p∗) as m→∞, r^*m 2 (1 - p^*) as m, mr∗→2 (1−p∗) as m→∞, with fluctuations of order O (m−1/2) O (m^-1/2) O (m−1/2). The proof is entirely combinatorial and relies on: A triangular 2-adic prefix automorphism An odd-unit residue permutation induced by the OptA lift congruence Exact binomial prefix counting under the mathematical lift measure A saddle-point analysis of linear barrier crossing No stochastic independence assumptions are required at any stage. The limiting constant 2 (1−p∗) =2−2log23≈0. 738140492857…2 (1 - p^*) = 2 - 2₂ 3 0. 7381404928572 (1−p∗) =2−log232≈0. 738140492857… arises deterministically from feasibility geometry and entropy-neutral prefix density under the lift congruence. This result isolates the large-scale geometry governing forced-prefix survival depth and provides a structural constant for the lift process in the rounded-critical regime.
Lando Hiler (Sun,) studied this question.