Delete a whole grapheme cluster with the forward Delete key

Found while testing crates/engine/src/cmd/text/caret.rs:60 (delete_dir, forward) with crates/model/src/edit.rs:423 (char_move)

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

crates/engine/src/cmd/text/caret.rs

@@ -56,7 +56,7 @@ pub(crate) fn delete_dir(s: &mut Session, dir: &str) -> Result<Value> {
             ed::delete(body, a, b)
         } else {
             let other = match dir.as_str() {
-                "forward" => ed::char_move(body, a, true),
+                "forward" => ed::cluster_end(body, a),
                 _ => {
                     // Backspace at the start of an indented/bulleted paragraph outdents first.
                     if a.1 == 0

crates/engine/src/tests.rs

@@ -98,6 +98,22 @@ fn text_editing_flow() {
     assert_eq!(s.doc().unwrap().selection.shapes.len(), 1);
 }
 
+/// Forward Delete removes a whole grapheme cluster, not just its first scalar.
+#[test]
+fn forward_delete_removes_whole_grapheme_cluster() {
+    for (input, rest) in [("\u{1F44D}\u{1F3FD}y", "y"), ("e\u{301}x", "x")] {
+        let mut s = session();
+        let title = s.doc().unwrap().current_slide().unwrap().shapes[0].id.0;
+        s.execute("text.edit", &json!({"id": title})).unwrap();
+        s.execute("text.selectAll", &json!({})).unwrap();
+        s.execute("text.insert", &json!({"text": input})).unwrap();
+        s.execute("text.move", &json!({"to": "start"})).unwrap();
+        s.execute("text.delete", &json!({"dir": "forward"})).unwrap();
+        let t = s.execute("text.get", &json!({"id": title})).unwrap();
+        assert_eq!(t["text"], rest);
+    }
+}
+
 /// `text.set` treats CRLF (or a lone CR) as one paragraph break and keeps no `\r` in the text.
 #[test]
 fn text_set_crlf_makes_clean_paragraphs() {

crates/model/src/edit.rs

@@ -3,6 +3,7 @@
 
 use crate::text::{Paragraph, Run, RunKind, RunProps, TextBody};
 use crate::words;
+use unicode_segmentation::UnicodeSegmentation;
 
 /// (paragraph, char offset in the paragraph).
 pub type Pos = (usize, usize);
@@ -419,6 +420,20 @@ fn smart_space(body: &mut TextBody, at: Pos) -> Pos {
     at
 }
 
+/// The position after the grapheme cluster at `pos`, or the next paragraph's start at a paragraph end.
+pub fn cluster_end(body: &TextBody, pos: Pos) -> Pos {
+    let (pi, ch) = clamp(body, pos);
+    let text = body.paragraphs.get(pi).map(Paragraph::text).unwrap_or_default();
+    match text.chars().nth(ch) {
+        Some(_) => {
+            let rest: String = text.chars().skip(ch).collect();
+            let n = rest.graphemes(true).next().map_or(1, |g| g.chars().count());
+            (pi, ch + n)
+        }
+        None => char_move(body, pos, true),
+    }
+}
+
 /// One character left/right across paragraph boundaries.
 pub fn char_move(body: &TextBody, pos: Pos, forward: bool) -> Pos {
     let (pi, ch) = clamp(body, pos);