cce887d69b
The --parallel worker did a full 7-party phaser barrier + kernel-lock dance around every single ~13-instruction interpreter block, making it 20x SLOWER than lockstep (2.7 vs 55 MIPS at n=400M) and JIT-less. Replace the single-block unlocked window with run_superblock_parallel_unlocked: a whole straight-line region on the extracted ctx + per-worker caches (block + JIT), stopping at the first import/halt/mmio/sync/budget boundary for the locked epilogue to handle. Touches zero KernelState in the lock-free window (thunk band cached once under the lock via new KernelState::thunk_addr_band). Same JIT seam as run_superblock, so XENIA_JIT unset = interp, set = JIT — one driver covers Phase A and B. Measured (--gpu-inline): - recovered the parallel path 16-30x (2.7 -> 43-95 MIPS) - video-phase n=2B parallel-JIT budget=8192: 21.0s vs lockstep-JIT 23.8s (+13%), but violently budget-fragile (4096 = 79.9s) -> the hard per-round barrier + load imbalance caps it well below the 4.3x runnable-width ceiling. Phase C (free-running workers) needed for the real multiplier. Determinism: lockstep path untouched; 6-config n=200M golden byte-identical (incl. config6 JIT+chain+budget=1 == interp+budget=1). xenia-jit 24 tests green; parallel_stress_short 20/20 ok. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>