seam-craft

A white flash appears when the two overlapping scene wrappers' summed opacity drops below 1 and the #root element has no opaque background, so the renderer's default white page shows through. Fix it by setting #root background to var(--canvas-deep, var(--canvas, #000)) in the assembled index.html.

Paint the stage ground by ensuring the assembler emits an opaque #root background, which assemble-index.mjs now does automatically. Any other consumer of the transition templates must provide the same guarantee so opacity dips composite over the dark canvas instead of white.

The injector extends the outgoing wrapper's data-duration to hold its final frame, pulls the incoming wrapper's data-start earlier to create the overlap window, and reassigns clip data-track-index as a 0/1 ping-pong so the wrappers never share a track. It then stamps the gsap_template into window.__timelines["main"] at the overlap start time.

No, same-track overlap is illegal under the composition lint rules in core/src/lint/rules/composition.ts. The injector avoids this by ping-ponging all clip track indices between 0 and 1, with the higher track compositing on top.

Yes, filter, scaleX, and transformOrigin are lint-clean on the master timeline because the gsap lint rule has no per-property whitelist and scopes checks to data-composition-id ranges. The x/y/scale/rotation/opacity whitelist is only a scene-worker prompt rule and does not bind index.html.

No, this Skill covers only the render-correctness doctrine and master-timeline mechanics shared by all transitions. The per-transition catalog such as crossfade, push-slide, zoom-through, and cut-the-curve lives in the separate transition registry.