Apply review fixes

- crates/model/src/edit.rs
- crates/engine/src/tests.rs

crates/engine/src/tests.rs

@@ -112,6 +112,17 @@ fn forward_delete_removes_whole_grapheme_cluster() {
         let t = s.execute("text.get", &json!({"id": title})).unwrap();
         assert_eq!(t["text"], rest);
     }
+    // Inside a cluster, Delete stops at that cluster's end and leaves the next flag intact.
+    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": "\u{1F1FA}\u{1F1F8}\u{1F1E8}\u{1F1E6}"})).unwrap();
+    s.execute("text.move", &json!({"to": "start"})).unwrap();
+    s.execute("text.move", &json!({"to": "right"})).unwrap();
+    s.execute("text.delete", &json!({"dir": "forward"})).unwrap();
+    let t = s.execute("text.get", &json!({"id": title})).unwrap();
+    assert_eq!(t["text"], "\u{1F1FA}\u{1F1E8}\u{1F1E6}");
 }
 
 /// `text.set` treats CRLF (or a lone CR) as one paragraph break and keeps no `\r` in the text.

crates/model/src/edit.rs

@@ -424,14 +424,15 @@ fn smart_space(body: &mut TextBody, at: Pos) -> Pos {
 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)
+    // Boundaries come from the whole paragraph, so a caret inside a cluster deletes only to its end.
+    let mut end = 0;
+    for g in text.graphemes(true) {
+        end += g.chars().count();
+        if end > ch {
+            return (pi, end);
         }
-        None => char_move(body, pos, true),
     }
+    char_move(body, pos, true)
 }
 
 /// One character left/right across paragraph boundaries.