G1: Remove Anchor Points selects the next anchor (#2241)

After Object › Path › Remove Anchor Points the anchor that follows each
removed one is selected: round the end of a closed subpath, or the one
before it at an open subpath's end. Running the command again goes on
along the path, without picking each anchor first. Several anchors,
subpaths and paths each get their own next anchor; a path that goes
leaves nothing selected; one undo step restores the anchors and the
selection.

The Delete key still selects the remainder whole so a second Delete
removes it, and the Delete Anchor Point tool still leaves the path
selected whole.

Fixes #2241

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/draw2.rs

@@ -1,6 +1,7 @@
 //! Commands backing the drawing tools (pencil, curvature, anchor tools, scissors, knife, eraser,
 //! blob brush, smooth, path eraser, join).
 
+use std::collections::BTreeSet;
 use std::sync::Arc;
 
 use kurbo::{CubicBez, ParamCurve, ParamCurveNearest};
@@ -60,7 +61,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Remove Anchor Points",
             ["Object", "Path"],
             None,
-            "{} remove the direct-selected anchors without opening their paths, refitting the curve round each → {removedObjects}",
+            "{} remove the direct-selected anchors without opening their paths, refitting the curve round each; the anchor after each removed one is selected, so running it again goes on along the path → {removedObjects}",
             has_anchors,
             remove_anchors
         ),
@@ -772,7 +773,16 @@ fn remove_anchors(s: &mut Session, _: &Value) -> Result<Value> {
         let mut removed = 0;
         let mut emptied = Beside::replacing(d, &jobs.iter().map(|(id, _)| *id).collect::<Vec<_>>());
         for (id, anchors) in jobs {
-            removed += usize::from(remove_anchors_of(d, sel, &mut emptied, id, anchors)?);
+            let shape: Vec<(usize, bool)> =
+                d.node(id).and_then(Node::path_data).map(|p| p.subpaths.iter().map(|sp| (sp.anchors.len(), sp.closed)).collect()).unwrap_or_default();
+            let next = following_anchors(&shape, &anchors);
+            if remove_anchors_of(d, sel, &mut emptied, id, anchors)? {
+                removed += 1;
+            } else if !next.is_empty() {
+                // The next anchor along is selected, so the next Remove Anchor Points goes on from
+                // there without picking it first (#2241).
+                sel.anchors.insert(id, next);
+            }
         }
         emptied.finish(d)?;
         Ok(removed)
@@ -780,6 +790,30 @@ fn remove_anchors(s: &mut Session, _: &Value) -> Result<Value> {
     Ok(json!({ "removedObjects": removed }))
 }
 
+/// Where the selection goes once Remove Anchor Points takes `removed` (subpath, anchor) out of a
+/// path whose subpaths have `shape` (anchor count, closed): in each subpath, the anchor after its
+/// last removed one, round the end of a closed subpath, or the one before it at an open subpath's
+/// end. Indexes are those after the removal, without the subpaths left with fewer than two anchors.
+fn following_anchors(shape: &[(usize, bool)], removed: &[(usize, usize)]) -> BTreeSet<(usize, usize)> {
+    let mut next = BTreeSet::new();
+    let mut kept = 0;
+    for (si, &(n, closed)) in shape.iter().enumerate() {
+        let gone: BTreeSet<usize> = removed.iter().filter(|&&(s, a)| s == si && a < n).map(|&(_, a)| a).collect();
+        if n - gone.len() < 2 {
+            continue;
+        }
+        if let Some(&last) = gone.last() {
+            let wrap = if closed { 0..last } else { 0..0 };
+            let after = (last + 1..n).chain(wrap).find(|a| !gone.contains(a));
+            if let Some(a) = after.or_else(|| (0..last).rev().find(|a| !gone.contains(a))) {
+                next.insert((kept, a - gone.range(..a).count()));
+            }
+        }
+        kept += 1;
+    }
+    next
+}
+
 /// Remove `anchors` (subpath, anchor) of path `id` without opening it, refitting the curve round
 /// each one. A subpath left with one anchor is removed, and a path left with no subpath is removed
 /// through `emptied`. True when the path went.