[miguel-heygen]

What

Opening a new track while moving clips in Studio no longer writes data-start / data-track-index onto untimed wrapper elements around those clips.

Why

Inside Studio, the preview runtime gives an id'd or animated untimed element a timing so the timeline can show it as a row. Opening a new track (dropping in the gap above or below the rows) renumbered every row of the file, so those wrappers were saved with data-start="0" and a track. The project then failed hyperframes check with video_nested_in_timed_element, which means a render with wrong frames. A drop onto an existing row writes only the dragged clip and was never affected. The same renumber also serves the z-order menu's "new track" move and asset drops into a new track, and the asset drop could fail outright next to such a wrapper.

Related work

The runtime marks the elements it times for discovery with data-hf-autostamped; its tests pin that stamping, so the runtime is unchanged. Editing such a row directly still makes its timing part of the file, as before.

How

Rows are tagged runtimeStamped where they are created from the manifest. The shared new-track layout (layoutAfterTrackInsert, used by all three paths) leaves those rows out of the renumber unless they are the dragged clip or part of the selection.

Test plan

• Unit tests added/updated. New pipeline tests go from a manifest row through the drag commit to the saved HTML: wrappers stay untimed, a selected wrapper is still renumbered, and an asset drop renumbers no wrapper. 3 of the 5 tests in the file fail without the fix; 5/5 three runs in a row. Studio player and hooks suites (3884 tests) pass.
• Manual testing performed. A wrapper fixture moved to a new track through the real commit path passes hyperframes check; before the fix it failed with three video_nested_in_timed_element errors. I did not drive a real browser.
• Documentation updated (not applicable).
• Comments follow CONTRIBUTING.md "Comments".

Before

main: one clip dragged to a new track, with three wrapper divs around clips. The saved index.html gains data-start="0" and a track on every wrapper, and hyperframes check fails with three video_nested_in_timed_element errors. This is the saved file and the check output, not a Studio screen: the browser harness available here shows no timeline rows.

After

This branch, the same move: only the dragged video's track changes, the wrappers are untouched, and hyperframes check passes (0 errors, 0 warnings).

[github-actions]

Edit accuracy: accurate 271 (base branch 271), smooth 127 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)

Unstable (1)

• seqplainkeys-none-pct-r0-root-z100: tracking 0.06, pressJump 0, drop 0, reload 0, render 0.03, renderKey -, undo false, teleport true / tracking 0.06, pressJump 0, drop 0, reload 0, render 0.03, renderKey -, undo true, teleport true / tracking 0.06, pressJump 0, drop 0, reload 0, render 0.03, renderKey -, undo true, teleport true