fix(pdf-import): take a group's knockout and isolate flags from the interpreter

The import read each form's /Group /I and /K from the file in order and
matched them to the transparency groups the interpreter pushed. The
interpreter draws a group that adds nothing (full opacity, Normal, no
mask, neither flag) straight onto its parent without pushing it, so every
group after one took another group's flags. Blend steps written as a
knockout group of falling opacity then painted over each other and drew
as solid dark shapes instead of light rings.

The interpreter already reports the flags right after pushing a group
(set_knockout, set_isolated); the import now uses those and drops the
file-order list. That list was capped at 10,000 entries, past which a page
failed to import; that limit goes with it.

docs/file-format-parity.md

@@ -1,6 +1,6 @@
 # File format parity
 
-> **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)
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-31 · **Change:** minor (PDF import: knockout and isolated groups keep their flags after a group drawn straight onto its parent) · **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 import (and a `.ai`'s PDF part): a transparency group's knockout and isolate flags (`/K`, `/I`; ISO 32000-1, 11.4.6.3) come from the interpreter as it pushes the group. They were read from the file in order and matched to the groups pushed, but a group that adds nothing (full opacity, Normal, no mask, neither flag) is drawn straight onto its parent without being pushed, so every group after one lost its own flags and took another's; and a page drawing form groups more than 10,000 times failed to import (the list of their flags was capped), which it no longer does. A blend's steps written as a knockout group of falling opacity drew as solid dark shapes: a user's `.ai` with 143 such bubbles now draws them as light rings, as poppler does (its bubble area 4.9% → 1.2% of pixels off from poppler's render); 16 other users' PDFs with transparency groups (44 pages) draw the same. Test `tests::import_fidelity::knockout_groups_after_a_group_drawn_straight_keep_their_flag`; 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. When a blend is the layer's last object and the layer's own state block (`7 () XW`, then `LB`) follows, the state is the layer's and the blend keeps its own, as for meshes (#4748); scores unchanged |
 | 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 |