fix(ai-import): compare a PDF of some artboards on the artboard its page shows

A PDF saved with Illustrator editing data for only some of its artboards
has pages for those artboards, while the editing data keeps them all. The
layers were compared with the first page on the first artboard, so a page
showing a later artboard never matched and the file came in as its PDF
part, without its layers.

With fewer pages than artboards, the first page is now taken to be the
artboard of its size whose art draws most like it (up to 16 weighed), and
the pages' type goes to that artboard and the ones after it. All the
artboards still come in, and the comparison still decides whether the
layers are used.

docs/file-format-parity.md

@@ -1,6 +1,6 @@
 # File format parity
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-30 · **Change:** minor (`.ai`/EPS editing data: a blend takes the transparency written after its record) · **Target:** Adobe Illustrator 2026 (30.x)
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-31 · **Change:** minor (PDF with editing data saved for some of its artboards: the layers are compared on the artboard its page shows) · **Target:** Adobe Illustrator 2026 (30.x)
 
 Every format Illustrator opens, places, saves or exports, against VectorCraft's format table (`FORMATS`,
 `OPEN_EXTS`, `PLACE_EXTS` in `crates/engine/src/cmd/fileio/formats.rs`). Illustrator's list comes from its public
@@ -132,6 +132,7 @@ the app's own editing copy of a file (an EPS after its `%%EOF`, a `.ai`'s `AIPri
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-31 | minor | PDF (and `.ai`) with Illustrator editing data saved with only some of its artboards: its pages are those artboards, while the editing data keeps them all, and the layers were compared with the first page on the first artboard, so a page of the second artboard came in as the PDF part, without its layers. With fewer pages than artboards, the first page is now taken to be the artboard of its size whose art draws most like it (up to 16 weighed), and the pages' type goes to that artboard and the ones after it. All artboards come in, as before. Test `import::tests_native::a_pdf_of_its_second_artboard_is_compared_on_that_artboard`; scores unchanged |
 | 2026-10-30 | minor | `.ai`/EPS editing data: a blend takes the transparency (opacity, blend mode, knockout; blends are written with knockout on) in the state block after its record, as a group takes the one after its end; it was left for the next object, so a blend's steps of falling opacity drew over each other instead of knocking each other out, and every such blend came in too dark (a user's file has 143, its bubbles came in as dark rings). Both a live blend and drawn steps kept as a group take it. Test `import::ai::tests::a_blends_transparency_follows_its_record`; checked locally against that file: it comes 1.3% → 0.6% nearer its page, though a mesh seen through a mesh-shaped opacity mask still keeps it just over the limit; scores unchanged |
 | 2026-10-30 | minor | `.ai`/EPS editing data: a gradient mesh with an opacity mask takes the transparency (`Xy`) written after the mask's dictionary, as one without a mask takes the one right after its `/End X!`; the operators of the mask's art (on `%_` lines) hid it, so the state was read as the next object's and each masked mesh in a run drew with the blend mode of the one before it (a Multiply shading drawn Normal, an Overlay tint drawn Multiply over the art below). Test `import::ai::tests::a_masked_gradient_mesh_takes_the_transparency_written_after_its_mask`; checked locally against a user's files: one opens from its layers 0.1% from its page (it was 0.6%, just inside the limit), another comes 1.6% → 1.3% nearer; scores unchanged |
 | 2026-10-30 | minor | `.ai`/EPS editing data: a layer's own state block (`Xy`, `Xd`, `7 () XW` before `LB`) can have the stroke style (`J`, `j`, `w`, `M`, `d`, `XR`) between its `Xy` and `Xd`; read as the art moving on, it lost the layer's opacity, so a layer at 17% drew opaque over the art under it and the file came in as its page. When the layer's last object is a gradient mesh, the mesh keeps its own state through the stroke style too (#4748). An object's own state block (`6 () XW`) still isn't the layer's. Of 408 users' files whose editing data was checked, 3 have such a block: an EPS that now opens from its layers 0.5% from its page (it was 18.8%), one whose layer now draws at 85% as its page does, and one whose layers are all at 100%; the others draw as before. Test `import::ai::tests::a_layers_state_keeps_through_the_stroke_style_written_in_it`; scores unchanged |