Integrate reviewed test changes from 7c1517de819741907fb945ea0ab7864734fa3856 and 340ba4e1dc6386581839c0b28c8fe8a1f4aeb70b unchanged. Document bounded 2D implementation, evidence and open gates; production source and historical manifests are unchanged.
Schedule test drives _pairs[i].explode/coalesce and patches _advance(index,
buffer) for the stale L1->L2 feed mutant; remap rejection test patches
_boundary_hosts entries and hierarchy.pairs instead of the read-only views;
the GPU launch-failure test patches _pairs[0].explode. Assertions unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>