Add-ons: Arrange Tools — Arrange in Grid, Swap, Replace with Top Object, Set Size of Each, Zoom to Selection

A built-in add-on in Object › Plug-ins › Arrange Tools (#4830, #4831, #4832, #4833, #4834):

- addon.arrange.grid lays the top-level selected objects out in rows and
  columns, a row or a column (stacking order from the back, visual bounds,
  each object centred in its cell), from the selection's top-left or
  centred on the artboard.
- addon.arrange.swap swaps two objects' bounds centres, and with `size`
  their widths and heights.
- addon.arrange.replace puts a copy of the topmost selected object centred
  on each of the others, in its stacking place, kept, stretched or fitted
  in proportion; the replaced objects are deleted unless `keep`.
- addon.arrange.size gives each selected object an exact width and/or
  height about a reference point.
- addon.arrange.zoomSelection (a UI command) fits the active view to the
  selection.

Places and sizes are measured as object.setBounds measures them (its
transform, now also available per object), strokes scale as Scale Strokes
& Effects says, each command is one undo step, and Arrange in Grid,
Replace with Top Object and Set Size of Each open previewed dialogs.
Catalog rows, command sweep cases, docs/mcp.md, parity docs and the
ROADMAP progress log.

crates/engine/src/cmd/object/bounds.rs

@@ -6,7 +6,7 @@ use super::{
 };
 
 pub(super) fn set_bounds(s: &mut Session, p: &Value) -> Result<Value> {
-    match bounds_transform(s, p, selected_roots_to_transform(s)?, 0.0)? {
+    match bounds_transform(s, p, selected_roots_to_transform(s)?, 0.0, true)? {
         Bounds::Anchors(ids, b) => set_anchor_bounds(s, p, ids, b),
         Bounds::Objects(ids, xf) => apply_transform(s, "Transform", ids, xf, p, false),
     }
@@ -32,7 +32,7 @@ pub(crate) fn bounds_rewrite(s: &Session, cmd: &str, params: &Value) -> Option<(
     if cmd != "object.setBounds" {
         return None;
     }
-    let Ok(Bounds::Objects(_, xf)) = bounds_transform(s, params, selected_roots_to_transform(s).ok()?, 1e-4) else { return None };
+    let Ok(Bounds::Objects(_, xf)) = bounds_transform(s, params, selected_roots_to_transform(s).ok()?, 1e-4, true) else { return None };
     let mut p = params.as_object().cloned().unwrap_or_default();
     for k in ["x", "y", "width", "height", "reference", "proportional"] {
         p.remove(k);
@@ -41,14 +41,26 @@ pub(crate) fn bounds_rewrite(s: &Session, cmd: &str, params: &Value) -> Option<(
     Some(("object.transform".to_string(), Value::Object(p)))
 }
 
+/// The transform that gives object `id` on its own the place and size `p` asks for, as
+/// `object.setBounds` measures them (Use Preview Bounds, `strokes`, `reference`, `proportional`),
+/// whatever anchors are direct-selected. The art keeps at least 1e-4 of its width and height.
+pub(crate) fn object_bounds_transform(s: &Session, p: &Value, id: NodeId) -> Result<Affine> {
+    match bounds_transform(s, p, vec![id], 1e-4, false)? {
+        Bounds::Objects(_, xf) => Ok(xf),
+        Bounds::Anchors(..) => Err(EngineError::Other("no bounds".into())),
+    }
+}
+
 /// How `object.setBounds` with params `p` changes the objects `ids`. A scale that would leave the
-/// art with a width or height below `least` of the one it has keeps `least` of it.
-fn bounds_transform(s: &Session, p: &Value, ids: Vec<NodeId>, least: f64) -> Result<Bounds> {
+/// art with a width or height below `least` of the one it has keeps `least` of it. With `anchors`,
+/// direct-selected anchors are what changes ([`Bounds::Anchors`]).
+fn bounds_transform(s: &Session, p: &Value, ids: Vec<NodeId>, least: f64, anchors: bool) -> Result<Bounds> {
     check_numbers(p, &["x", "y", "width", "height", "reference"], "object.setBounds")?;
     let st = s.doc()?;
     check_switches(p, &TRANSFORM_SWITCHES, "object.setBounds")?;
     check_switches(p, &["proportional"], "object.setBounds")?;
-    if transforms_objects(p)
+    if anchors
+        && transforms_objects(p)
         && !bool_or(p, "copy", false)
         && let Some(b) = effects::preview::anchor_bounds(&st.selection, &st.doc, s.prefs.use_preview_bounds)
     {