fix: keep deleted equations out of the numbering

src/render.rs

@@ -141,6 +141,17 @@ fn render_added_or_deleted(block: &Block, tag: DiffTag, out: &mut String) {
             )
             .unwrap();
         }
+        // A deleted equation must not take a number, or every later number
+        // shifts by one. The set rule is scoped to the wrapper.
+        Block::Equation { content, .. } if tag == DiffTag::Deleted => {
+            write!(
+                out,
+                "#{}[#set math.equation(numbering: none)\n{}]",
+                func,
+                escape_content(content, escape_refs)
+            )
+            .unwrap();
+        }
         // Raw blocks and equations are content-mode; they can be wrapped.
         Block::RawBlock { content } | Block::Equation { content, .. } => {
             write!(out, "#{}[{}]", func, escape_content(content, escape_refs)).unwrap();

tests/integration.rs

@@ -209,3 +209,13 @@ fn test_indented_line_comment_does_not_split_paragraph() {
     // A whitespace-only line would be treated as a paragraph break by Typst.
     assert!(!output.contains("\n  \n"));
 }
+
+#[test]
+fn test_deleted_equation_takes_no_number() {
+    let old = "#set math.equation(numbering: \"(1)\")\n\n$ y $\n\n$ z $ <eq-z>\n\nSee @eq-z.\n";
+    let new = "#set math.equation(numbering: \"(1)\")\n\n$ z $ <eq-z>\n\nSee @eq-z.\n";
+    let output = run_diff(old, new);
+
+    // Numbered, the deleted equation would push `@eq-z` from (1) to (2).
+    assert!(output.contains("#diff-deleted[#set math.equation(numbering: none)\n$ y $]"));
+}