Per review feedback on PR #364: the 'hero vanishes' failure has two
mechanisms. Primary: second tween's immediateRender overwrites the first
at construction time. Secondary: tl.from() resets to its declared from-
state when seeked past timeline end, which the capture engine triggers.
Both are now named so the rule has precise rationale, not just a pattern
to avoid.
Ref: https://github.com/heygen-com/hyperframes/pull/364#pullrequestreview-4167523103
Add five animation-authoring rules to step-6-build.md that the linter
cannot catch but that silently ship broken output. Surfaced from two
independent builds (2026-04-20) where compositions passed lint and
still rendered elements invisible / unscrubbing.
Rules added:
- No iframes for captured content (don't scrub)
- Never stack transform tweens on one element (entrance + Ken Burns
on same img silently kills it)
- Prefer tl.fromTo() over tl.from() inside .clip scenes
(immediateRender interacts badly with scene boundaries)
- Ambient pulses must attach to seekable tl, not standalone gsap.to()
- Generalize the caption hard-kill rule to every scene-boundary exit
Alex Coulombe