Normalise CRLF in replace_text before computing the diff

Found while testing crates/model/src/edit.rs:420-439 (replace_text), reached from crates/engine/src/cmd/slide.rs:556 (notes)

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

crates/model/src/edit.rs

@@ -418,6 +418,8 @@ fn pos_of_char(body: &TextBody, mut n: usize) -> Pos {
 /// keeps its run and paragraph formatting and new text takes the formatting where it lands. Text
 /// that shares nothing with the old text replaces it as plain text.
 pub fn replace_text(body: &mut TextBody, text: &str) {
+    // Normalise line endings first so the common prefix/suffix cannot split a `\r\n` pair.
+    let text = &text.replace("\r\n", "\n").replace('\r', "\n");
     let old: Vec<char> = body.text().chars().collect();
     let new: Vec<char> = text.chars().collect();
     if old == new {
@@ -723,6 +725,22 @@ mod tests {
         b
     }
 
+    #[test]
+    fn replace_text_crlf_matches_from_text() {
+        // The kept suffix must not start inside a `\r\n` pair.
+        let mut b = TextBody::from_text("x\ny");
+        replace_text(&mut b, "z\r\ny");
+        assert_eq!(b.text(), "z\ny");
+        // CRLF in the kept prefix, and the same text with CRLF changes nothing.
+        let before = notes();
+        let mut b = before.clone();
+        replace_text(&mut b, "Overview\r\nFirst point\r\nSecond point");
+        assert_eq!(b, before);
+        replace_text(&mut b, "Overview\r\nFirst point\r\nSecond\rpoint");
+        assert_eq!(b.text(), "Overview\nFirst point\nSecond\npoint");
+        assert_eq!(b.paragraphs[0].runs[0].props.bold, Some(true));
+    }
+
     #[test]
     fn replace_text_keeps_formatting() {
         let before = notes();