Simulation.get_ddf() is flat (9*ny*nx); view it as (Q, cells) before applying the fluid mask, with a flat-DDF regression. Label A/E as runner-like force-read workloads (values discarded, no aggregation or validation; no macro/probe/CSV cost; not benchmark throughput) and split status lines into CONSTRUCTED and WARM_READY. Test/doc only. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>