pimsim-nn Oracle Invariant

backend-simulators/pim/pimsim-nn is the performance oracle. Its simulation behavior defines the hardware model used for Raptor/PIMCOMP comparisons.

Required invariant

Do not add instruction or operator support to pimsim-nn.
Changes to pimsim-nn must preserve simulation behavior exactly. Acceptable changes are limited to behavior-neutral maintenance proven not to alter simulated timing, scheduling, power, energy, or supported input programs.
Unsupported pimsim-nn operations must remain unsupported; do not approximate their timing or map them onto another operation.
Adapt compiler inputs to the oracle instead. For YOLO, use validation/networks/pimcomp_models/yolo11n/yolo11n-pimsim-nn.onnx, the dedicated pimsim-ready performance artifact with Softmax operations removed. Use validation/networks/yolo11n/depth_51/yolo11n_depth_51.onnx for YOLO functional validation; removing Softmax changes the model's numerical behavior, so the pimsim-ready artifact is not a correctness reference.

Any proposed pimsim-nn behavior change requires explicit user authorization and must not be introduced as part of a compiler optimization.