Escape carriage return as 
 in XML text content

Found while testing crates/pptx/src/xml.rs:363 (esc)

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

crates/pptx/src/xml.rs

@@ -367,6 +367,7 @@ pub fn esc(s: &str) -> String {
             '&' => o.push_str("&"),
             '<' => o.push_str("&lt;"),
             '>' => o.push_str("&gt;"),
+            '\r' => o.push_str("&#13;"),
             c if xml_char(c) => o.push(c),
             _ => {}
         }
@@ -506,6 +507,15 @@ mod tests {
         assert_eq!(t, vec!["one\ntwo\nthree\rfour".to_string(), "x\ny".to_string()]);
     }
 
+    #[test]
+    fn cr_in_text_survives_write_read() {
+        assert_eq!(esc("a\rb"), "a&#13;b");
+        let mut w = W::default();
+        w.elt("a:t", "one\rtwo\r\nthree");
+        let d = parse(w.s.as_bytes()).expect("parse");
+        assert_eq!(d.root.text(), "one\rtwo\r\nthree");
+    }
+
     #[test]
     fn parse_basic_and_entities() {
         let d = parse(b"<?xml version=\"1.0\"?><a:p xmlns:a=\"x\"><a:r><a:t>A &amp; B &#x41; &lt;</a:t></a:r><a:x r:id=\"rId1\" id=\"5\"/></a:p>")