feat(cli): determinism guard — reframe lint enforces scene purity (0.6.42)

[kiyeonjeon21]

What

OSS floor hardening for reframe-studio. Two audits this session (a fundamentals review + an agent-surface audit) converged on one confirmed crack in the determinism floor: scenes must be pure functions of time, but nothing enforced it. A scene using Math.random()/Date compiles and renders fine yet yields a different IR each compile, silently breaking the reproducibility the product's whole pitch rests on. The golden tests only cover IR→render; the source→IR step was unguarded.

How

reframe lint now verifies purity for .ts sources (the studio-readiness gate, alongside addressability):

• bundle the scene once, evaluate it twice, deep-compare the two IRs
• emit a non-deterministic-render finding pinned to the first differing address (e.g. nodes[0].props.x changed 0.42 → 0.97) plus a source-scan hint at the culprit construct
• same --strict exit-code gate

New in-process checkDeterminism(path) exported via reframe-video/compile so an embedder can verify a freshly generated scene before trusting it.

Load-bearing detail: loadScene imports a data:…base64 URL, and Node caches ESM by URL — so a naive double-load returns the same cached module and misses module-level nondeterminism. The two evals append distinct cache-busting comments so the module re-evaluates fresh. The test asserts the impure scene IS caught, guarding this.

Verification

• 395 tests pass (+4 determinism tests); typecheck clean; reframe-video build bundles checkDeterminism into dist/compile-api.js
• Goldens byte-identical (this only adds a check; no IR/eval-path change)
• reframe lint examples/scenes/photo-montage.ts → no determinism finding (pure); a temp scene with Math.random() → flagged with nodes[0].props.x, --strict exits 1

Scope

Focused on the one confirmed floor crack. Ranked follow-ups noted in the plan (not built): addressing-density lint, structured validation errors, renderFrameAt export, timing-walk unification. Version → 0.6.42.

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