Part of #1429: path, Pathfinder and live-object commands add and remove many objects in one pass

Offset Path, Outline Stroke, the Pathfinder panel, Clean Up, Make
Blend, Rasterize and the other commands that #1429's table marks 3,
except Split Into Grid, added, removed or replaced their objects one at
a time, and so did Remove Anchor Points, Redefine Symbol and the
removal of Shaper groups whose source art is gone. Each insertion or
removal moved the later objects of the layer or group. The lookups by
id that followed walked the tree, and every fourth walk rebuilt the
lookup cache. On 25,000 rectangles a release build of vectorcraft-cli
took 29.1 s for Offset Path.

These commands now make their edits with Document::wrap,
Document::insert_beside and Document::remove_many, in one pass over the
children of each layer or group, and Outline Stroke and Expand write
each new object into the place of the object it replaces. A list that
holds an object twice, or an object and another inside it, and that was
edited without an error before, is still edited one object at a time.
The documents, selections and undo steps are the same. On the same
rectangles Offset Path now takes 1.3 s.

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

crates/engine/src/cmd/patterncmds.rs

@@ -18,6 +18,7 @@ use vectorcraft_doc::{Document, Node, NodeId, NodeKind, Selection};
 use vectorcraft_geom::Rect;
 
 use super::edit::selected_roots;
+use super::pathops::Beside;
 use super::*;
 
 pub fn specs() -> Vec<CommandSpec> {
@@ -633,15 +634,12 @@ fn make_repeat(s: &mut Session, p: &Value, label: &str, make: impl Fn(Vec<Arc<No
         return Ok(json!({ "id": r.0 }));
     }
     let roots = roots(s, p)?;
-    let Some(&top) = roots.last() else { return Err(EngineError::Other("select the art to repeat".into())) };
+    if roots.is_empty() {
+        return Err(EngineError::Other("select the art to repeat".into()));
+    }
     let id = s.edit(label, |d, sel| {
-        let (par, idx, _) = d.position(top).ok_or(EngineError::NoNode(top))?;
-        let nodes: Vec<Arc<Node>> = roots.iter().filter_map(|id| d.node(*id).cloned()).map(Arc::new).collect();
         let id = d.alloc_id();
-        d.insert(par, idx + 1, Node::new(id, NodeKind::Repeat(make(nodes))))?;
-        for r in &roots {
-            d.remove(*r)?;
-        }
+        d.wrap(&roots, |nodes| Node::new(id, NodeKind::Repeat(make(nodes))))?;
         sel.set([id]);
         Ok(id)
     })?;
@@ -682,15 +680,14 @@ fn repeat_release(s: &mut Session, _: &Value) -> Result<Value> {
     let reps = selected_repeats(s);
     let ids = s.edit("Release Repeat", |d, sel| {
         let mut out = vec![];
+        let mut released = Beside::replacing(d, &reps);
         for r in &reps {
             let Some(n) = d.node(*r).cloned() else { continue };
-            let (par, idx, _) = d.position(*r).ok_or(EngineError::NoNode(*r))?;
-            d.remove(*r)?;
-            for (k, c) in n.children().into_iter().flatten().enumerate() {
-                out.push(c.id);
-                d.insert(par, idx + k, (**c).clone())?;
-            }
+            let art: Vec<Node> = n.children().into_iter().flatten().map(|c| (**c).clone()).collect();
+            out.extend(art.iter().map(|c| c.id));
+            released.put(d, *r, art)?;
         }
+        released.finish(d)?;
         sel.set(out.iter().copied());
         Ok(out)
     })?;