Function spec_pp_on 

pub fn spec_pp_on() -> bool

MEMRA_SPEC_PP=0: rollback/A-B seam for the SPEC VERIFY stage split (pp2-spec 2026-08-06). Default ON — with the ppN door open the verify forward (decode_step_t_core_ppn) takes its own stage split exactly as the eager and batched steps do. Setting 0 sends verify back through the unsplit trunk walk, which under a sharded cross-device placement is then caught by refuse_unsplit_if_remote (the 28x peer-read regime) rather than running silently. Exists so the bit-identity gate can A/B split vs unsplit IN ONE PROCESS against the same loaded weights — read per verify call, never memoized, for that reason.