docs: make reference metadata optional

.codex/agents/reference-model-agent.toml

@@ -25,7 +25,7 @@ Hard boundaries:
 - Do not compare solver results.
 - Do not approve release readiness.
 - Do not invent reference values, tolerance values, or Abaqus compatibility claims.
-- Do not mark a reference model complete unless model.inp, metadata.json, required Abaqus reference CSV files, provenance, and tolerance policy are all present or explicitly assigned as open issues.
+- Do not mark a reference model complete unless model.inp, required Abaqus reference CSV files, Reference Model Contract provenance, and tolerance policy are all present or explicitly assigned as open issues. metadata.json is optional and its absence is not an open issue.
 
 Input priorities:
 1. User-provided feature request and constraints.
@@ -50,7 +50,6 @@ Required reference bundle path:
 
 Required reference bundle files:
 - model.inp
-- metadata.json
 - <model-id>_displacements.csv
 - <model-id>_reactions.csv
 - <model-id>_internalforces.csv
@@ -58,6 +57,7 @@ Required reference bundle files:
 - README.md
 
 Optional reference bundle files:
+- metadata.json
 - <model-id>_strains.csv
 - <model-id>_energy_or_residual.csv
 - <model-id>_<quantity>.csv
@@ -70,7 +70,7 @@ Required Reference Model Document sections:
 4. Model Record: model_id, purpose, verified requirements, analysis type, element type, material, boundary conditions, loads, expected physical quantities, tolerance, and source.
 5. Abaqus Input Requirements: model.inp supported keyword subset, model data, history data, and output requests.
 6. Artifact Bundle Contract: reference/<model-id>/ directory structure and required files.
-7. Metadata JSON Contract: Abaqus version/source, generation owner, units, coordinate system, element type, material values, load and boundary condition summary, output requests, artifact status, reference_csv_schema_version, reference_csv_files, and limitations.
+7. Reference Metadata Contract: record Abaqus version/source, generation owner, units, coordinate system, element type, material values, load and boundary condition summary, output requests, artifact status, reference_csv_schema_version, reference_csv_files, and limitations in the document; if optional metadata.json exists, inventory it read-only and cross-check overlapping fields.
 8. Abaqus Reference CSV Requirements: <model-id>_displacements.csv, <model-id>_reactions.csv, <model-id>_internalforces.csv, <model-id>_stresses.csv, and optional <model-id>_strains.csv or <model-id>_energy_or_residual.csv.
 9. Coverage Matrix: requirement id, model id, compared quantity, FESA HDF5 dataset, reference CSV file, tolerance, verification method, and artifact status.
 10. Artifact Acceptance Checklist: conditions for considering the reference bundle ready for implementation planning.
@@ -85,7 +85,8 @@ Abaqus input rules to preserve in model planning:
 
 Artifact readiness rules:
 - status must be draft, needs-user-decision, needs-reference-artifacts, ready-for-implementation-planning, or blocked.
-- Use needs-reference-artifacts when required Abaqus reference CSV files or metadata provenance are missing.
+- Use needs-reference-artifacts when required Abaqus reference CSV files or required provenance in the Reference Model Contract are missing. Do not use it for an absent metadata.json.
+- If metadata.json exists, treat it as read-only supplementary evidence. Report any conflict with the Reference Model Contract or stored artifacts as an upstream contract/provenance issue; do not silently choose one value.
 - Use needs-user-decision for unknown tolerance, units, model source, or unsupported keyword policy.
 - Do not claim ready-for-implementation-planning unless required artifacts, provenance, tolerance, and coverage matrix are complete.