Now that a lane is generic, the obvious next move is to read a clip dropped on
another clip as "put it inside that symbol". It cannot mean that: dropping a
clip on occupied lane time already means it claims that time and trims the
incumbent. Structural nesting therefore needs an explicit affordance -- a grab
handle with `grab`/`grabbing` cursors, distinct from the body's temporal move
and the edges' trims -- and its drop must route through `nest/move-node`, which
preserves world transform and root timing, rather than through a weaker
`:parent` assignment that would make a drawing jump when it is rehoused.
The second half of the note is what expansion should be. One permanently
expanded row per lane clip is the vertical growth the one-row lane exists to
avoid, so an expanded lane shows exactly one portal: the currently selected
clip, swapped in place when the selection changes, not following the playhead.
The portal header is the structural drop target, sub-expanding it walks the
source symbol's lanes through the existing recursive root-time mapping, and
collapsed clips carry their instance-level keys as ticks. The cost of
inspection stays constant.
No lane-as-symbol type and no second ownership edge: the hierarchy is still
symbol, lane, clip, source symbol, its nodes. Lane membership owns time; a
symbol instance owns composition. Written before the interaction is built,
because the capability it protects is easy to lose by accident.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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