The eye on an expanded sub-composition child always rendered as "Hide",
whatever the source said. One click hid the element and every click after
that rewrote the same attribute, so the row could never be shown again,
not even after a reload, since data-hidden is in the file.
buildChildElements synthesizes a child row from a manifest clip with no
element to read, and compensated by inheriting hidden/timelineLocked/
timelineRole/fxChain/automation from the child's flat store twin. That
twin does not exist for a real sub-composition: processTimelineMessage
drops any clip whose parent composition is itself in the manifest before
building the flat store, so the lookup always missed and the inheritance
was dead code for the one case it was written for. It worked only for a
phantom-wrapper parent, where the child does keep a store entry.
Read the state off the live element instead. collectSubCompositionHostState
walks each sub-composition host in the preview document and records the
data-* state of every id'd descendant, keyed by dom id. The existing
sibling walk cannot serve this: it defines which rows exist and writes
parentMap, and it stops at the first id'd descendant, so scene footage
sitting one level below an id'd region wrapper is never reached. The new
walk descends the whole subtree and touches neither rows nor parentage.
Reproduced on a 9-scene storyboard project where every scene is a
sub-composition. Before: a scene video and title carrying data-hidden both
announced "Hide track N", and clicking left the file byte-identical. After:
both announce "Show track N", and hide/show round-trips the attribute.
A top-level clip with the same attribute always announced "Show", which is
what made the gap specific to expanded child rows.
The existing regression test passed throughout because its fixture hands
the child a flat twin with hidden: true and gives the host no
compositionSrc, so the child key falls back to the index.html scope and a
twin can exist. The added test models a real sub-composition instead.
