* fix(fig): give every layer on an exported canvas its own order key
Figma orders siblings by `parentIndex.position`. Shared styles, the
variable records and a canvas's own layers are written in three passes,
all landing on the internal canvas, and each numbered from the first
key — so up to five siblings claimed `!`. Exporting gold-preview left
402 records under one canvas with keys repeating up to five times.
Each pass now continues the keys already written for that canvas.
Counting them per canvas also covers the ordinary pages, whose layers
are written after the internal resources.
* fix(fig): keep the order keys a layer was imported with
Saving a document renumbered every sibling from the first key, so a
round trip rewrote positions Figma had assigned even where nothing
moved. A layer now keeps its imported key where that still orders it
after the previous sibling, and takes a key between its neighbours
otherwise.
Canvas children are excluded: shared styles and variable records are
written to the internal canvas by other passes that continue the keys
already there, so an imported key could collide with one of theirs.
Co-authored-by: mrhard9090 <74858909+mrhard9090@users.noreply.github.com>
* refactor(fig): look a sibling's order key up by id
`exportOrderKey` runs once per child and scanned the sibling list for
the node, so a parent with many layers cost O(n²) to export. The cached
entry now maps id to key directly.
Covers all three writers in the canvas test as well: an internal canvas
with its own layers, a shared style, and two variable collections, so
the pass boundaries that restarted a sequence are exercised rather than
only the page and variable passes.
* refactor(core): name the GUID type in the canvas order key test
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Co-authored-by: mrhard9090 <74858909+mrhard9090@users.noreply.github.com>
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