Tip: Datamimic makes a coding agent prove its test data model before the data exists

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Datamimic (MIT, Python, 96 stars, surfaced on HN 2026-09-16) generates byte-identical synthetic test data for the same seed, and its agent workflow is the interesting part: the agent preserves intent as JSON, submits a scaffolding request via CLI, gets machine-readable validation diagnostics back, and repairs the model until it reports `verified=true`. That is a concrete verification gate for the common failure where an agent writes tests against a fixture world it invented and the tests pass for the wrong reason. The determinism guarantee also makes the fixtures usable in CI and compliance audits.