Symbols: same-edge 9-slice art shrinks when the instance is smaller

With both guides of an axis past the same edge, the art keeps its size
from the other edge of the instance, or shrinks to the instance's width
or height when the instance is smaller than the art. The module doc,
AxisMap::new and the docs/target-app-parity.md entry now say so.

crates/doc/src/symbol_nine_slice.rs

@@ -15,7 +15,8 @@
 //! Use 9-slice scaling section). VectorCraft's own rules for that: a guide past an edge of the art
 //! cuts the art at that edge, so the outer cell on its side holds no art; with both guides of an
 //! axis past opposite edges the art scales as a whole along it; with both past the same edge the
-//! art lies in the outer cell at the other edge and keeps its size, from that edge of the instance.
+//! art lies in the outer cell at the other edge and keeps its size, from that edge of the instance,
+//! or shrinks to the instance's width or height when the instance is smaller than the art.
 //!
 //! The guides are stored as fractions of the symbol's natural size, measured from the left and top
 //! edges and from the right and bottom edges, so they survive resizing the art. A fraction below 0
@@ -212,7 +213,8 @@ impl AxisMap {
     /// The axis from `lo` to `hi` (`lo < hi`) with guides `near` and `far` (fractions of its
     /// length in from each end, `near + far < 1`; either may lie past an end), scaled by `k`
     /// (above 0). With both guides past the far end the art keeps its length from the scaled
-    /// start, and with both past the near end it keeps its length up to the scaled end.
+    /// start, and with both past the near end it keeps its length up to the scaled end; when the
+    /// scaled length is shorter than the art, the art shrinks to the scaled length.
     fn new(lo: f64, hi: f64, near: f64, far: f64, k: f64) -> Self {
         let len = hi - lo;
         let c1 = (lo + near * len).clamp(lo, hi);

docs/target-app-parity.md

@@ -876,7 +876,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - Symbol editing mode keeps every instance in step: instances of a dynamic symbol inside other symbols' art, pattern tiles, graph designs, stored brushes and opacity masks keep their appearance changes on the objects an edit reorders and drop the changes to objects it deletes. The view does not draw the instance the edit was entered from. Area type in the symbol's art takes the text wrap that moving a wrap object gives it. Editing another symbol at a place that fails keeps the current edit open, and only the editing layer or art on it can be isolated. Tests: `crates/engine/src/tests/symboledit.rs`, `isolation::symbol_editing_does_not_draw_the_instance_it_was_entered_from`, `panels::symbols::tests::double_clicking_a_symbol_in_the_panel_edits_it_in_either_view`, `the_panel_menus_edit_symbol_edits_the_instances_symbol_or_the_panels`, `the_control_bars_edit_symbol_edits_the_selected_instances_symbol`, `chrome::tests::the_control_bar_exits_symbol_editing_mode`.
   - **Dynamic symbol instances on the canvas** ([Symbols, archived copy](https://web.archive.org/web/20240206075757/https://helpx.adobe.com/illustrator/using/symbols.html)): each instance of a dynamic symbol can have an appearance of its own while it shares the symbol's shape. The rest of this entry is VectorCraft's own rules. A Direct Selection click on an instance of a dynamic symbol selects the path, compound path or type object of the symbol's art under the pointer and outlines it (`symbol.instance.selectPart`); the Swatches and Color panels, the Control bar, the Eyedropper and the other fill and stroke controls then change that object's fill or stroke (solid, none, gradient or pattern) for this instance only, each as one undo step, and `transparency.set` changes its opacity and blend the same way; the symbol's art and its other instances stay as they were. Alt or Shift picks the instance whole. An Eyedropper source that is not a path, compound path or type, a click on any other object of the art (a group, image, blend or nested instance) and the commands that change the selected objects (moving, Delete, Group, Hide, Lock, Arrange, Expand, the gradient annotator, isolate/knockout on Transparency, the Appearance panel's rows and others) are refused with a status message. Copy, Export Selection, Fit to Selection, Liquify, Isolate, Add to Library and Save Selection use the whole instance (`docs/mcp.md`), and another selection tool selects the instance whole again. Tests: `crates/engine/src/tests/dynamic_symbols.rs` (`gradients_and_patterns_on_a_picked_object_are_taken`, `opacity_and_blend_on_a_picked_object_go_through_transparency_set`), `direct::tests::a_click_on_a_dynamic_instance_picks_the_object_under_the_pointer`.
   - **9-slice guides on the canvas** ([public source](https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/maintain-proportions-while-scaling-symbols.html)): while a symbol with Enable Guides for 9-Slice Scaling on is edited in symbol editing mode, the canvas draws its two horizontal and two vertical guides as dotted lines across its art, with any tool and with ruler guides hidden. With the Selection tool the pointer near a guide shows the Move cursor, and dragging the guide moves it (`symbol.options`'s `nineSliceGuides`) as one undo step; Escape during the drag puts it back. VectorCraft's own rules: a guide within 4 screen pixels takes the press before the art and the bounding box; it may pass the art's edges (see the next entry) and stops short of the opposite guide; the drag does not snap. Tests: `nineslice::tests`, `symbol_nine_slice::tests::the_edited_symbols_guides_cross_its_art_where_the_editing_layer_shows_it`, `a_moved_guide_passes_the_arts_edges_and_stops_short_of_the_opposite_guide`, `canvas::tests::the_edited_symbols_nine_slice_guides_are_drawn_and_dragged_on_the_canvas`.
-  - **9-slice guides outside the art** ([the help page](https://help.adobe.com/archive/en/illustrator/cs6/illustrator_reference.pdf), Use 9-slice scaling section): a guide may lie outside the symbol's art, set by dragging it past the art's edge in symbol editing mode, by `symbol.options`'s `nineSliceGuides` or by a Symbol Options field below 0% or above 100%, and a scaled instance still scales, by the cells its art falls in. VectorCraft's own rules: each guide lies within 16 times the art's width or height of its edge (`-16..16` as a fraction, `-1600..1600` in percent) and the two guides of an axis keep their order; a guide past an edge of the art cuts the art at that edge, so the outer cell on its side holds no art; with both guides of an axis past opposite edges the art scales as a whole along it; with both past the same edge the art lies in the outer cell at the other edge and keeps its size, from that edge of the instance; Symbol Options shows and keeps the guides unrounded. Native files keep the guides exactly; SVG and `.ai` write such an instance as its placed art and keep no guides. Tests: `symbol_nine_slice::tests::guides_outside_the_art_are_accepted_in_order_and_within_the_limit`, `art_scales_by_the_cells_it_falls_in_when_guides_lie_outside_it`, `the_map_with_guides_outside_the_art_is_continuous_and_monotone` in `crates/doc`, `guides_outside_the_art_are_set_by_command_and_scale_by_the_cells_that_hold_art`, `a_guide_dragged_past_the_arts_edge_lies_outside_it`, `guides_outside_the_art_survive_saving_and_reopening_a_native_file` in `crates/engine`, `nineslice::tests::a_guide_outside_the_art_is_taken_and_dragged_past_the_arts_edge`, `a_nine_slice_instance_with_a_guide_outside_its_art_is_written_as_drawn` (SVG and `.ai`).
+  - **9-slice guides outside the art** ([the help page](https://help.adobe.com/archive/en/illustrator/cs6/illustrator_reference.pdf), Use 9-slice scaling section): a guide may lie outside the symbol's art, set by dragging it past the art's edge in symbol editing mode, by `symbol.options`'s `nineSliceGuides` or by a Symbol Options field below 0% or above 100%, and a scaled instance still scales, by the cells its art falls in. VectorCraft's own rules: each guide lies within 16 times the art's width or height of its edge (`-16..16` as a fraction, `-1600..1600` in percent) and the two guides of an axis keep their order; a guide past an edge of the art cuts the art at that edge, so the outer cell on its side holds no art; with both guides of an axis past opposite edges the art scales as a whole along it; with both past the same edge the art lies in the outer cell at the other edge and keeps its size, from that edge of the instance, or shrinks to the instance's width or height when the instance is smaller than the art; Symbol Options shows and keeps the guides unrounded. Native files keep the guides exactly; SVG and `.ai` write such an instance as its placed art and keep no guides. Tests: `symbol_nine_slice::tests::guides_outside_the_art_are_accepted_in_order_and_within_the_limit`, `art_scales_by_the_cells_it_falls_in_when_guides_lie_outside_it`, `the_map_with_guides_outside_the_art_is_continuous_and_monotone` in `crates/doc`, `guides_outside_the_art_are_set_by_command_and_scale_by_the_cells_that_hold_art`, `a_guide_dragged_past_the_arts_edge_lies_outside_it`, `guides_outside_the_art_survive_saving_and_reopening_a_native_file` in `crates/engine`, `nineslice::tests::a_guide_outside_the_art_is_taken_and_dragged_past_the_arts_edge`, `a_nine_slice_instance_with_a_guide_outside_its_art_is_written_as_drawn` (SVG and `.ai`).
   - **Delete Symbol asks first** ([Symbols panel](https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/symbols-panel-options.html), [symbol libraries](https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/create-or-import-symbol-libraries.html), [Alt-click Delete](https://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html)): the Symbols panel's Delete Symbol button and menu item ask "Delete the selected symbol?" with Yes and No for a symbol no instance uses. For a symbol with placed instances they ask with Expand Instances (the instances become ordinary art), Delete Instances and Cancel; either Instances button deletes the symbol in one undo step. Alt-click on the button deletes an unused symbol without asking and still asks about one with instances. A question left open while another document became active deletes nothing. `symbol.delete` itself does not ask. Tests: `panels::symbols::tests::delete_symbol_asks_first_and_alt_click_deletes_an_unused_symbol_at_once`, `the_in_use_question_expands_or_deletes_the_instances`, `a_stale_delete_symbol_question_deletes_nothing`, `the_delete_symbol_questions_show_their_buttons`.
   - **Symbols › Select All Unused** ([Symbols panel](https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/symbols-panel-options.html), #4918): the Symbols panel menu's Select All Unused shows the symbols nothing places selected (`symbol.unused`): instances in the art (opacity masks included), graph designs, pattern tiles and brush art count, and so do instances in a used symbol's art. Delete Symbol, the button or the menu item, then asks "Delete the selected symbols?" once and deletes those still unused in one undo step (`symbol.delete {names}`); Alt-click on the button deletes them without asking, and a click on a symbol picks just it again. Tests: `tests::brushsym::symbol_unused_lists_the_symbols_nothing_places_and_delete_takes_several`, `panels::symbols::tests::select_all_unused_picks_the_unused_symbols_and_delete_deletes_them`, `dialogs::symbol_delete::tests::several_symbols_get_the_plural_question`.
   - **Symbols › Sort by Name and the list views** ([the help page](https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/symbols-panel-options.html)): the Symbols panel menu's Sort by Name puts the symbols in alphabetical order (`symbol.sortByName`), and its Thumbnail View, Small List View and Large List View show them as thumbnails, in a compact list or in a list with larger thumbnails. VectorCraft's own rules: the sort ignores case and keeps names that differ only in case in their order; it changes the document's order, which `symbol.list` reports, as one undo step, keeps the current symbol and adds no undo step when the symbols are already in order; Thumbnail View is the default, Small List View has 18-point rows with 14-point thumbnails and Large List View 26-point rows with 22-point thumbnails, and a click or double-click on a symbol does the same in every view. Tests: `tests::brushsym::symbol_sort_by_name_orders_the_symbols_in_one_undo_step`, `panels::symbols::tests::sort_by_name_and_the_small_and_large_list_views`.