Enforce versioned artifact contract in exported study outputs

[cmccomb]

Summary

Turn the published artifact contract into an executable guarantee by enforcing schema-version fields and validating exported study outputs in tests.

Why

• The public contract page is only trustworthy if exported artifacts are checked against it.
• design-research-analysis and umbrella integration work need stable machine-validated fields.
• Versioned validation will make future schema evolution safer.

Proposed work

• Add explicit schema or version markers to exported artifacts where required by the public contract.
• Add validation helpers or fixtures for study.yaml, manifest.json, conditions.csv, runs.csv, events.csv, and evaluations.csv.
• Add regression tests that fail on missing required fields or unsupported version changes.
• Document how version changes are communicated to downstream packages.

Acceptance criteria

• Exported artifacts include documented version markers where the contract says they should.
• Tests cover the canonical artifact set and fail clearly on contract drift.
• Downstream adapter work can rely on the validated surface instead of internal serialization details.