proofsheet-core

Local-first browser control for two jobs that turn out to be the same job: producing store-ready screenshots at exact dimensions, and running deterministic tests against a real browser.

Both need the same three things — a driver, a way to make the page stop being nondeterministic, and a record of what happened that can be checked later. So they share one core.

Design commitments

• The model never authors code or selectors. Actions are typed; the runtime composes them. A free-text field in a tool schema is grammar-constrained to any text, so the field is removed rather than validated after the fact.
• Output pixels are the source of truth. Stores specify pixels; the viewport is derived. See [device].
• Determinism is injected, not hoped for. See [determinism].
• Nothing is claimed without a negative control. A check that cannot fail on correct input is not evidence.

Dependencies

Deliberately small. No async runtime, no browser automation framework: a tool people install should not drag a dependency tree behind it.