{
  "design_status": "Specified before executing the benchmark; designed mechanical counterexample, not an external validation dataset.",
  "seed": 20260910,
  "units": {"displacement":"mm", "force":"N", "stiffness":"N/mm"},
  "members": [[12.0,1.2,0.6],[4.0,2.0,0.4]],
  "parameter_order": ["k", "Y", "H"],
  "preload": 0.8,
  "gains": [1.0,2.0],
  "frame_stiffness": 20.0,
  "probe_displacement": 0.45,
  "probe_noise_sd": 0.15,
  "target_legs": [[0.0,1.2,241],[1.2,0.15,211],[0.15,0.9,151]],
  "virtual_records": 512,
  "sweep": {"stiffness_ratios":[2.0,3.0,4.0], "target_gains":[1.5,2.0,3.0], "preloads":[0.65,0.8,0.95]},
  "noise_sensitivity": [0.05,0.15,0.30],
  "methods": {
    "point": "Posterior mean parameters, with the entire common loading history replayed. Strong point control.",
    "parameter_only": "Exact joint parameter posterior, but virgin states at transfer. Explicit history-removal ablation, not all Bayesian methods.",
    "unpaired": "Exact parameter and state marginals, independently recombined at transfer. Removes persistent parameter-state association.",
    "pact": "Exact joint parameter-state law, with each realization continued from its committed state.",
    "bayes_replay": "Exact joint parameter posterior plus full deterministic history replay. Equivalence control."
  },
  "conditioning": "All methods receive the identical posterior weights computed with one common physical observation operator, prior and Gaussian likelihood. No method-specific fit. Before the probe the weights are exactly one half by permutation symmetry.",
  "scores": ["trajectory_RMSE_N", "trajectory_energy_score_N", "90_percent_marginal_coverage", "90_percent_marginal_width_N", "distance_to_exact_conditional_mean_N"],
  "evaluation": "Initial transfer predicts the full target. After one probe, score only later target increments; the probe is excluded. Virtual truths are independent branch draws and probe noise. No experimental accuracy claim.",
  "verification": ["independent piecewise-linear equilibrium oracle", "committed-state immutability", "algorithmic tangent finite differences away from switches", "exact work/storage/dissipation by event splitting", "increment halving", "exact Bayesian replay equivalence", "symmetry and virgin controls"]
}