`nest/inside` walked a row path only through instances. Every node has
the same two maps to its parent, so the walk now steps into any node:
inside an instance is the symbol it places, inside a shape is where its
points and keys are. The selected shape at any depth is `inside` over
its full path, which gives the stage editor its handles (through the
matrix, drags back through the inverse) and the inspector the shape's
own frame to key at, and the time map back for jumping to a key.
`inside` resolves only the node's lineage: where a node is depends on
its parents and nothing else, and resolving the whole symbol cost more
than a stage frame (7.9ms against 3ms on the swarm; now 0.09ms).
Checked equal to the whole-symbol resolve on every node and frame of
the swarm, two instances deep.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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