Cover repeated DOCX style replacement across saves (#2469)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/docx/tests/it/fixtures.rs

@@ -48,6 +48,40 @@ fn read_body(body: &str) -> Document {
     wordcraft_docx::read(&docx(body, &[], &[])).unwrap()
 }
 
+#[test]
+fn repeated_style_ids_use_last() {
+    let styles = format!(
+        r#"<w:styles {W_NS}>
+        <w:style w:type="paragraph" w:styleId="Repeated"><w:name w:val="First"/>
+          <w:pPr><w:spacing w:after="240"/></w:pPr><w:rPr><w:b/><w:smallCaps/><w:sz w:val="28"/></w:rPr>
+        </w:style>
+        <w:style w:type="paragraph" w:styleId="Repeated"><w:name w:val="Last"/>
+          <w:pPr><w:spacing w:before="120"/></w:pPr><w:rPr><w:i/><w:caps/><w:sz w:val="20"/></w:rPr>
+        </w:style></w:styles>"#
+    );
+    let bytes = docx(
+        r#"<w:p><w:pPr><w:pStyle w:val="Repeated"/></w:pPr><w:r><w:t>Original style probe</w:t></w:r></w:p>"#,
+        &[("styles", "styles", "styles.xml")],
+        &[("word/styles.xml", &styles)],
+    );
+    let mut document = wordcraft_docx::read(&bytes).unwrap();
+    for round in 0..=2 {
+        let style = document.styles.get("Repeated").unwrap();
+        assert_eq!(style.name, "Last");
+        assert_eq!(style.chr.size, Some(10.0));
+        assert_eq!(style.chr.italic, Some(true));
+        assert_eq!(style.chr.bold, None);
+        assert_eq!(style.chr.caps, Some(true));
+        assert_eq!(style.chr.small_caps, None);
+        assert_eq!(style.para.space_before, Some(6.0));
+        assert_eq!(style.para.space_after, None);
+        assert_eq!(document.styles.styles.iter().filter(|style| style.id == "Repeated").count(), 1);
+        if round < 2 {
+            document = wordcraft_docx::read(&wordcraft_docx::write(&document).unwrap()).unwrap();
+        }
+    }
+}
+
 #[test]
 fn paragraph_default_presence_survives_repeated_saves() {
     // Omission leaves paragraph defaults application-defined (ISO 29500 pPrDefault).