ADR-003: Pure render(t) and determinism rules

• Status: accepted · Date: 2026-10-15

Decision

The visual state is a pure function of (timeline, t):

• no wall clock, no CSS animations/transitions (forced off by the base stylesheet), no Math.random;
• randomness comes from seeded hashes (rnd(seed), mulberry32) keyed by element id and frame index;
• state changes are derived from states[] up to t (with $since times), never accumulated.

Consequences

• Any frame can be rendered in any order by any worker (NFR-4, tested by rendering frames {0, 90, 179} in different orders and comparing SHA-1s).
• Partial re-render and scrubbing in the studio are trivially correct.
• Components must be written as functions of time; a unit test renders the gallery forwards and backwards and compares the DOM.