Form D build agent discovered: our point-add circuit contains no
Hadamard or S gates (only X/CX/CCX/CZ/CCZ/SWAP/R/HMR/Z/NEG).
State never leaves the computational basis. Aaronson-Gottesman
tableau compression buys nothing when superposition does not
exist; reduces to exactly what sim_gpu.cu already does at one
bit per qubit per shot.
Toffoli fraction measured 13.87% (well under the 40% threshold
the planner flagged). The 1.07x cuda-sim-ops-bin ceiling traces
to memory-bandwidth on per-shot striped state — not algorithm.
STABSim-class wins remain valid for QEC / surface-code work where
H + S exist; that's a future workload.
Two replacement directions queued:
1. axis-flip sim_gpu.cu — per-candidate parallelism over per-shot.
~3 days. Reuses BSHK new op_id; no AG tableau.
2. ops.bin packing — 56→16 B per op halves global-memory traffic.
Addresses the actual bottleneck.
Catalog + public bend.html both updated. Form D progress doc at
examples/cuda-fanout/plans/form-D-build-progress.md documents the
structural reasoning in full.
russell@unturf.com
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