Artboards: copied artboards take a free id and keep their own guides

Duplicate Artboards, the Artboard tool's Alt-drag (artboard.move with
copy) and Paste of a copied artboard gave the new artboard the largest
artboard id plus one, saturating. In a document with an artboard id
of 4,294,967,295 (u32::MAX), which only a hand-made file has, the copy
got that same id. Artboard guides record the id of their artboard.
Deleting either of the two artboards with that id then deleted the
guides of both, and guide.list reported the copy's guides on the
other one.

push_artboard_copy now takes the id from Document::next_artboard_id,
as artboard.new and Convert to Artboards do. Since the #1718 fix, that
function returns the smallest free id when the largest is u32::MAX.
In a document whose artboard ids are all below u32::MAX, a copy gets
the same id as before.

Docs: docs/target-app-parity.md.

crates/engine/src/cmd/panelcmds.rs

@@ -166,7 +166,7 @@ pub(crate) fn copy_artboard(d: &mut vectorcraft_doc::Document, i: usize, dv: Vec
 /// (`<name> copy 2`…) when that is taken → its index.
 pub(crate) fn push_artboard_copy(d: &mut vectorcraft_doc::Document, src: &vectorcraft_doc::Artboard, rect: Rect) -> usize {
     let mut a = src.clone();
-    a.id = d.artboards.iter().map(|a| a.id).max().unwrap_or(0).saturating_add(1);
+    a.id = d.next_artboard_id();
     let taken = |name: &str| d.artboards.iter().any(|a| a.name == name);
     a.name = [src.name.clone(), format!("{} copy", src.name)]
         .into_iter()

crates/engine/src/tests_panelcmds.rs

@@ -197,6 +197,48 @@ fn artboard_tool_cut_removes_the_artboard_and_its_art() {
     assert_eq!((d.artboards.len(), d.node(r).is_some()), (2, true), "the cut is one undo step");
 }
 
+/// A copy of an artboard whose id is the largest there is (only a hand-made file has one, #1718)
+/// takes an id that no other artboard has, as a new artboard does, whether Duplicate Artboards, the
+/// Artboard tool's Alt-drag (`artboard.move` with `copy`) or Paste makes it. Deleting either
+/// artboard then leaves the other's guides.
+#[test]
+fn copied_artboards_take_a_free_id_and_keep_their_own_guides() {
+    let mut got = vec![];
+    for (cmd, p) in [
+        ("artboard.duplicate", json!({"index": 0})),
+        ("artboard.move", json!({"index": 0, "dx": 0, "dy": 900, "copy": true})),
+        ("edit.paste", json!({})),
+    ] {
+        let mut s = Session::new();
+        let mut d = vectorcraft_doc::Document::new(800.0, 600.0);
+        d.artboards[0].id = u32::MAX;
+        s.add_document(d, None);
+        s.execute("guide.add", &json!({"vertical": true, "pos": 100, "artboard": 0})).unwrap();
+        if cmd == "edit.paste" {
+            s.execute("artboard.copy", &json!({"index": 0})).unwrap();
+        }
+        s.execute(cmd, &p).unwrap();
+        // Each pass deletes one artboard (the copy, then the original), adds the artboard ids of
+        // the remaining guides to `kept`, and undoes the delete.
+        let mut kept = vec![];
+        for i in [1, 0] {
+            s.execute("artboard.delete", &json!({"index": i})).unwrap();
+            kept.push(s.doc().unwrap().doc.guides.iter().map(|g| g.artboard).collect::<Vec<_>>());
+            s.execute("edit.undo", &json!({})).unwrap();
+        }
+        got.push((cmd, s.doc().unwrap().doc.artboards.iter().map(|a| a.id).collect::<Vec<_>>(), kept));
+    }
+    let max = Some(u32::MAX);
+    assert_eq!(
+        got,
+        [
+            ("artboard.duplicate", vec![u32::MAX, 1], vec![vec![max], vec![Some(1)]]),
+            ("artboard.move", vec![u32::MAX, 1], vec![vec![max], vec![Some(1)]]),
+            ("edit.paste", vec![u32::MAX, 1], vec![vec![max], vec![]]),
+        ]
+    );
+}
+
 #[test]
 fn swatch_groups_duplicate_sort() {
     let mut s = session();

docs/target-app-parity.md

@@ -462,6 +462,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - **Path editing (#494):** the handles shown are the handles that drag: Direct Selection drags those of a path selected as a whole (as the Pen leaves it), the Anchor Point tool and Pen+Alt no longer grab handles that Show handles when multiple anchors are selected hides, a handle shorter than the tolerance leaves its anchor to be picked, and the anchor tools pick within Selection & Anchor Display › Tolerance. A dragged segment keeps a smooth anchor at either end smooth. With Direct Selection, the Pen, the Curvature and the anchor tools, a path selected as a whole shows all its anchors selected, and the Control bar and the Properties panel offer Convert (corner, smooth) for them too; Remove and Cut wait for anchors direct-selected (#504). A handle drag gathers its snap targets once per drag (it took 21 ms per pointer move on a 20,000-path document, now 1 ms; `vectorcraft-cli perf` measures handle and segment drags on a 5,000-anchor path). Join merges the selected anchor points that lie on one another, as after Average, into one anchor (#1582, fixes #1533); Average and Join in one step, with a corner or smooth choice for the joined anchor, is missing ([gap 1](gaps.md)).
   - **Graphs:** Column, Stacked Column, Bar, Stacked Bar, Line, Area, Scatter, Pie and Radar graph tools with Graph Data and Graph Type. A series starts in greyscale; Group Selection's fill and stroke are kept separately on the graph and reapplied when its data, type or size changes, and through save, open and undo. Graph Type's Override Calculated Values (both `axisMin` and `axisMax`) uses exactly that value-axis range, split into the tick count (5 when automatic). Line graphs take Edge-to-Edge Lines (off by default: the points sit at the centres of their categories; graphs saved before the option keep their edge-to-edge lines), and radar graphs follow Mark Data Points and Connect Data Points. Blank cells (an empty CSV cell or `null`) are values left out, not zeros: columns, bars and stacked segments skip them, lines and scatter lines break around them and the value axis ignores them, while area, pie and radar draw them as 0; a number in straight quotes is a label, and the data window writes it back quoted. Graph types combine: Graph Type on series picked with Group Selection (or `series` indexes) draws them as their own type, with column, stacked column, line and area mixing on the vertical value axis and bar and stacked bar on the horizontal one; stacked columns take one slot of the cluster, lines draw in front of columns and areas behind. The value axis goes on the left, the right or both sides (column, stacked column, line, area and scatter graphs; bar graphs keep theirs along the bottom), and Separate Scales gives the series assigned to the right axis a scale of their own with its own tick values. Each value axis takes tick marks of no, short or full (across the plot) length and a count per division, and a prefix and suffix for its numbers; the category axis takes tick marks too (none by default), at or between its labels. Graph designs: Object › Graph › Design lists the designs with a preview of the selected one, and New Design (the selected art), Rename, Delete Design, Paste Design (a copy back to edit) and Select Unused, and Marker draws the data points and legend swatches of line, scatter and radar series with a design, scaled so its backmost object fills the default marker's square. Graph Data transposes rows and columns and switches a scatter graph's x and y, and a `|` in a category or series label starts a new line. Pie graphs take Legends in Wedges, Position (Even, Ratio sized by area, Stacked on one centre) and Sort (None, All, First). Graph Type takes column and cluster widths up to 1000% (overlapping past 100%) with First Row and First Column in Front (First Row orders each series' categories; across series the series order decides, so series stay one group each for Group Selection), draws filled lines, adds drop shadows behind columns, bars, lines and wedges, and puts the legend in rows across the top. Text formatted with the Character or Appearance controls, on the whole graph or on labels picked with Group Selection, is kept per kind of label (value axis numbers, category labels, legend labels) through the graph being drawn again. Object › Graph › Data opens a worksheet: cells picked with a click and edited above the sheet (Tab moves right, Enter down, the arrows between cells), Import Data from a tab-separated text file, Transpose, Switch x/y, Cell Style (decimals shown, column width), Revert and Apply. Column designs remain open. `graph.setData` returns and takes the data as CSV with each value written exactly, not rounded to two decimals, so applying the returned CSV changes nothing (#1485).
   - **Other:** Eyedropper, Gradient annotator, Artboard (Alt-drag duplicates an artboard, and its art with Move/Copy Artwork with Artboard on; Copy, Cut and Paste take the artboard with its art, Paste right of the last artboard, Paste in Place where it was, into this or another document, #446; Object › Artboards › Rearrange All Artboards lays them out in a grid by row or by column, in one row or one column, left to right or right to left, from the menu, the Artboards panel or Properties' Rearrange All, #681; Scale Artwork with Artboard, in the Control bar and Properties beside Move Artwork with Artboard, resizes the artboard proportionally with the art fully inside it and its guides, strokes and corners per the Scale preferences, #602), Measure, Type, Hand, Zoom, Rotate View.
+    Duplicate Artboards, the Artboard tool's Alt-drag and Paste give the new artboard an id that no other artboard has, also when an artboard's id is the largest possible value (#1718). Deleting the copy or the original then leaves the other's guides.
   - **Editing type:** double-clicking type with a selection tool switches to the Type tool with the caret where it was clicked.
   - **Temporary tools:** Cmd with any other tool drags with the selection tool used last (Selection, Direct Selection or Group Selection). Held Space pans and Cmd+Space zooms (Cmd+Alt+Space out) whatever the tool.
   - **Panel drag and drop:** art dragged off the canvas onto the Symbols panel becomes a symbol, onto the Swatches panel a pattern swatch and onto the Brushes panel an Art brush; a symbol dragged onto the canvas places an instance where it is dropped, and a brush dragged onto a path is applied to it.