The store-to-preview sync no longer applies a partial selection: if a resolvable member's
DOM node is not ready yet it bails and retries on the next effect run, so the write-back can
never shrink the store's selection by dropping an unresolved member.
Marquee row hit-testing reuses shouldShowTimelineLayerGroupHeader instead of re-deriving
the group-header placement rule, keeping one owner for that predicate.
The DOM-selection to timeline sync routes through the canonical resolveTimelineIdForSelection
(source-file, ancestor, active-comp fallback) instead of a narrow domId/id match that
mismatched sub-composition clips.
The preview-sync equality check compares selection as sets both ways and includes the
anchor, so duplicate resolutions no longer mask an unsynced member.
Extract resolveTimelineIdForSelection so DOM-to-timeline id mapping lives in one place
with a single sourceFile / activeCompPath / index.html fallback, fixing a sub-composition
selection that previously diverged between callers.
Extract shared start-trim delta helpers used by both single-clip and group resize, and
remove the never-called refreshDomEditGroupSelectionsFromPreview.
Miguel Angel Simon Sierra