Artboard tool: buttons on the selected artboard's edges add an artboard beside it

Squashed from #6111 onto main.

docs/mcp.md

@@ -4186,6 +4186,15 @@ selects them. `edit.paste {artboardsAt: [x, y]}` instead centers the copied artb
 value that is not `[x, y]` fails with `` `artboardsAt` must be [x, y] ``. `artboard.duplicate {index? | indices?, art?}` does the same in one step → `{index, indices, ids}`.
 Window › Artboards › Duplicate Artboards passes the selected artboards (those the Artboard tool has selected, else the
 active one) as `indices`, and a row dragged onto New Artboard passes its artboard as `index`.
+`artboard.new {beside?, side}` adds an empty artboard the size of artboard `beside` (default: the last), 20 pt from
+that side of it, and `artboard.duplicate {index, side}` puts the copies there instead, together as they lay on that side
+of the artboards they copy; `side` is `"left"`, `"right"`, `"top"` or `"bottom"`. Another `side` fails with
+`` `side` must be "left", "right", "top" or "bottom" ``, `beside` without `side` fails with `` `beside` needs `side` ``,
+and `artboard.new` refuses `side` given with `x`, `y`, `width` or `height`; each leaves the document and its undo
+history as they were. With the Artboard tool and one artboard selected, a button with a plus shows just outside the
+middle of each edge where an artboard of the same size fits on that side (within the canvas and overlapping no other
+artboard): a click runs `artboard.new {beside, side}`, an Alt-click `artboard.duplicate {index, side, art: true}`, and
+the new artboard becomes the active one. An Alt-click on a locked artboard's button does nothing.
 `artboard.move {copy: true, moveArt: true}` is the Artboard tool's Alt-drag. `artboard.duplicate` and `artboard.move`
 also move the pattern tiles of the copies when `patterns` is true (default: prefs `transformPatternTiles`);
 `edit.paste` leaves the tiles of a pasted artboard's art where they were.

docs/target-app-parity.md

@@ -620,6 +620,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Artboard Escape routing:** Escape leaves Artboard editing for Selection; during a drag it first cancels the gesture. Headless egui key events cover idle Escape, active-drag cancellation and a subsequent Escape in `tests/distortkeys.rs`.
 - **Escape in the distort tools:** Escape during a Puppet Warp pin drag or turn, a Perspective Grid tool handle or plane widget drag, a Perspective Selection move, resize or plane widget drag, or a Liquify stroke cancels it: the art goes back to how the press found it, no undo step is added, and the tool stays chosen. Puppet Warp also selects again the pins selected before the press, and Escape during a Liquify Alt-drag puts the brush size back. Regression tests: `escape_cancels_*` in `crates/tools/src/distort/puppet.rs`, `perspective.rs` and `liquify.rs`, and `escape_cancels_a_puppet_warp_perspective_or_liquify_drag` in `tests/distortkeys.rs`.
 - **Shift with the Artboard tool:** a Shift-click adds an artboard to the selection or takes it out when the button comes up. A Shift-drag inside an artboard draws a new artboard there, and a Shift-drag on the pasteboard is a marquee that toggles the artboards it touches, as the [default keyboard shortcuts](https://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html) (a Shift-drag draws an artboard within an existing one) and [Using multiple artboards](https://web.archive.org/web/20210925094818/https://helpx.adobe.com/illustrator/using/using-multiple-artboards.html) (archived copy) describe. Shift no longer keeps an artboard move at 45° steps or a drawn artboard square. Escape during a marquee or while a new artboard is being drawn cancels it and keeps the Artboard tool. Pointer and key tests in `crates/tools/src/xform/artboard.rs` cover the four gestures and Escape.
+- **Artboard edge buttons:** with the Artboard tool and one artboard selected, a button with a plus shows just outside the middle of each edge where an artboard of the same size fits on that side; clicking it adds an empty artboard of that size there (`artboard.new {beside, side}`), and Alt-clicking duplicates the artboard with its art there (`artboard.duplicate {index, side}`), each in one undo step, with the new artboard active. An Alt-click on a locked artboard's button does nothing, as the tool doesn't copy a locked artboard. The 20 pt gap and the room rule (within the canvas, overlapping no other artboard) are VectorCraft's own. Pointer tests in `crates/tools/src/xform/artboard/tests.rs` and an engine test in `tests/panelcmds.rs` cover it. Public references: [Add artboards instantly](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/add-edit-artboards/add-new-artboards.html) and [Duplicate artboards instantly](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/add-edit-artboards/duplicate-artboards.html).
 - **Artboard deletion keys:** Delete/Backspace delete selected boards in one Undo step, retaining the original first board in the current order when all are selected, as in the public [Delete artboards guide](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/add-edit-artboards/delete-artboards.html). The last board and active drags stay protected; neither key clears selected artwork. Headless shortcut regressions in `tests/distortkeys.rs` cover reordered boards, artwork, saved state and Undo/Redo.
 - **Locked artboards:** a click in the Artboards panel's lock column locks or unlocks an artboard in one undo step (`artboard.setProps {index, locked}`), and the native format saves the lock. The Artboard tool doesn't move, copy, resize or delete a locked artboard, Rearrange and Fit to Artwork Bounds leave it as it is, and its name isn't edited on the canvas. The art on it (each object whose bounds overlap it, a group as one object) acts as locked art until it is unlocked: clicks, marquees, `select.set`, `select.all` and the tools pass over it, and commands that act on the selection leave it; art drawn or pasted onto it stays selected and editable until the selection leaves it out. Tests in `crates/doc/src/lib.rs`, `tests/panelcmds.rs`, `xform/artboard.rs`, `panels/artboards.rs` and `canvas.rs` cover them. Public references: [Lock artboards](https://helpx.adobe.com/illustrator/desktop/create-manage-artboards/organize-manage-artboards/lock-artboards.html) and [Managing Artboards in Illustrator](https://creativepro.com/managing-artboards-in-illustrator/).
 - **Linux RPM packaging:** 64-bit runtime capabilities replace Fedora-specific required package names (#1275); glibc 2.35, libm and libgcc_s are declared alongside dynamically loaded xkbcommon and Vulkan/EGL. Generated x86_64/aarch64 metadata and isolated synthetic-provider resolution checked; real-distro install/start-up QA remains pending.