{
  "experiment": "SRP-RIGIDITY-01",
  "james_message": "996d837f-0c33-4d66-9d14-849cef60e1e2",
  "locked_at": "2026-09-10T19:10:00Z",
  "support_rule": {
    "joint_share_ge_0_5_plus_six_sign": "WITHDRAWN_AS_CONFIRMATORY",
    "retained_in_history": true,
    "descriptive_label": "SUPPORTED_DESCRIPTIVELY",
    "scope": "HOUSE_ENDPOINT_TREND_ONLY",
    "senate": "MIXED",
    "general_elite_rigidity": "NOT_ESTABLISHED"
  },
  "measurement_families": {
    "nominate_geometry": [
      "N1",
      "N3"
    ],
    "brookings_party_unity": [
      "N2"
    ],
    "independent_family_count_claim": "TWO_LINES_NOT_THREE"
  },
  "alternatives": [
    {
      "id": "A",
      "name": "NOMINATE scaling/career-score artifact",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Recompute N1/N3 with session-only or freshman-only scores vs career NOMINATE"
    },
    {
      "id": "B",
      "name": "Party sorting/realignment composition change",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Recompute N1 after party-affiliation-change adjustment (Southern realignment)"
    },
    {
      "id": "C",
      "name": "Roll-call agenda selection",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Fixed vote-type subsample; procedural vs substantive split"
    },
    {
      "id": "D",
      "name": "Chamber rules/institutional differences",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Senate contrary N1 as primary chamber-asymmetry construct (not nuisance)"
    },
    {
      "id": "E",
      "name": "Shared roll-call provenance / Brookings continuity",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Map 8-4 vintage/normalization lineage by year; keep frozen hashes; no splice"
    },
    {
      "id": "F",
      "name": "Two-party sorting without broader system rigidity",
      "disposition": "PLAUSIBLE",
      "discriminating_test": "Cross-system non-elite measures (out of RIGIDITY-01 scope); do not escalate here"
    }
  ],
  "rigidity_02_execution": "NOT_AUTHORIZED",
  "theory_exposure": "INDEPENDENT_BUT_THEORY_EXPOSED_REVIEW",
  "refs": {
    "claude_adjudication": "39ca9ed4",
    "astra_provenance": "cbf82874 / astra:bc41c8a0",
    "astra_synthesis_relay": "14d6c891",
    "brookings_audit": "41ae1339"
  }
}