read_accepted now distinguishes size==1 dangling orphans (warn+drop) from
structural corruption / role duplication (raise), and runs explicit binding
checks (video_id/task_type/flip_axis) that survive python -O. add() validates
before evicting the buffered partner so pending_orphans can recover it.
PairPendingBuffer collects pair members by pair_id and emits units;
write_accepted does tmp+os.replace atomic write; read_accepted rebuilds
units and drops disk-dangling orphans. Pure helper; on_accept wiring is
Phase 2 (real write point: adversarial_filter.write_final_bank).
iomgaa