Running ONNX Runtime transformers GPU pytest (dispatch-verified)

Reusable, hard-won knowledge for running the Python transformers tests under onnxruntime/test/python/transformers/ against a GPU-built wheel, on a box where torch is also installed. Three gotchas below will each cost you an hour if rediscovered. See the ort-test skill for the general test taxonomy and the false-green modes; this skill is the GPU + transformers + SDPA-dispatch specialization.

1. NEUTRAL-CWD gotcha — never run pytest from the repo root

Symptom:

ModuleNotFoundError: No module named 'onnxruntime.capi'
# or an AttributeError deep inside onnxruntime import