The Studio stack rebuild (#2291) landed the remaining NLE layers but dropped
or regressed several final-wave behaviors from the reviewed studio-dnd stack,
and never repaired the stale timelineZones.ts that #2279 introduced. Restores:
- TimelineRuler: sticky under vertical scroll, full-height gridlines removed
(beat lines only), frame-number tick labels via a persisted timeDisplayMode
store preference (PlayerControls toggle now store-backed)
- timelineZones: stable track lanes — lane = authored data-track-index
ascending; z is paint order only (replaces the stale z-driven lane pack,
which broke track insert-band commits that contractually depend on it)
- persistTimelineBatchEdit: a batch member whose patch is a no-op (attributes
already at target values, e.g. in a track-insert renumber) is skipped
instead of aborting and rolling back the whole batch — this alone made
new-track creation (incl. the top insert band) fail silently
- useTimelineStackingSync: unresolvable clips read as NaN again so
timelineStackingSync's Number.isFinite exclusion contract holds (z=0
fabrications skewed stacking boundaries)
- timelineAssetDrop: drops land on the drop track (no overlap bump to
max-track+1), data-hf-id stamped, audio gets data-volume
- timing edits: soft-reload the server's rewritten GSAP script instead of a
full iframe remount (no all-clips flash on move/resize); full reload only
when no scriptText or the soft path can't apply, and one full reload when a
group edit touches non-active files (new hooks/timelineTimingSync.ts)
- duration: content-driven grow-AND-shrink on move/resize/delete, synced
optimistically to the store and the live root data-duration at release
(was a grow-only ratchet; shrink never updated the readout)
New UX: sidebar asset click opens a compact non-modal preview over the canvas
(dismiss on outside click, Escape, playback, or seek), and clicking an
already-added asset reveals its clip in the timeline (smooth minimal scroll
to its time and lane; vertical-only in fit zoom).
Verified by pointer-driving a real project: sticky ruler + gridline removal,
no iframe remount on move/resize (marker survives, GSAP tween positions
rewritten in place), duration readout 40->37->40 on shrink/stretch, and
top-insert-band track creation renumbering lanes correctly on disk.
