[miguel-heygen]

What

runtimeElementWindow looks up the root composition only for elements that carry data-composition-id. Every other timed node skips the lookup.

Why

#6354 made the root's clip window open-ended and decided "is this the root" with findRootCompositionElement. That lookup ran for every timed node, and for every timed ancestor clipChainVisibleAt walks, on every visibility pass. Each call is one or two document-wide querySelectors, and without [data-root="true"] the first one scans the whole document. So a full pass (every renderSeek frame) grew roughly as timed nodes × DOM size. Only a data-composition-id element can be the root, so other nodes never need the query. Raised in review of #6354 after it had been queued.

How

const isRoot = compId !== null && rawNode === findRootCompositionElement(rawNode.ownerDocument); Same result for every node, with no query for the non-composition ones.

Test plan

• Unit tests added/updated

• Manual testing performed

• Documentation updated (if applicable)

• Comments follow CONTRIBUTING.md "Comments": they say why, not what, and a bug fix says what the code must do and how to reproduce the bug

• timeline.test.ts 72/72, including fix(core): a root without data-duration stays on screen after its GSAP timeline ends #6354's root-vs-nested-scene window test.

• fix(core): a root without data-duration stays on screen after its GSAP timeline ends #6354's two browser tests in coreRuntimeBrowser.test.ts (root with no data-duration, clip inside a discovery-stamped wrapper) pass 3 runs in a row with this change.

• Pre-commit lint, format, typecheck and fallow pass.

Small on purpose: a one-line follow-up to #6354's review, kept apart so it lands on its own.

[github-actions]

Edit accuracy: accurate 271 (base branch 271), smooth 132 of those

The gate passes.
Smoothness is reported in the artifact, not gated. A case fails only if it fails 2 of 3 runs.

Quarantined, measured but not gated (0)

[heygengenesis]

Verdict: APPROVE · 0 blocker · 0 important · 0 nits · head 5de45c8a

This is exactly equivalent to the old check. findRootCompositionElement only returns elements that match [data-composition-id], so a node without that attribute could never equal it. !== null (rather than a truthy check) keeps an empty data-composition-id="" root working. CI is green.