fix: treat inline equations as atomic tokens in word-level diff

src/diff.rs

@@ -180,6 +180,17 @@ fn tokenize_mixed(s: &str) -> Vec<&str> {
                 // Standalone '#'
                 tokens.push(&s[start..i]);
             }
+        } else if c == '$' && !s[..i].ends_with('\\') {
+            // Inline equation: keep `$...$` as one atomic token.
+            // A `$` preceded by a backslash is an escaped
+            // literal dollar sign in markup, not a math delimiter.
+            let start = i;
+            i += 1;
+            match s[i..].find('$') {
+                Some(off) => i += off + 1,
+                None => i = s.len(),
+            }
+            tokens.push(&s[start..i]);
         } else if c == '@' {
             // Typst reference: @label (alphanumeric, hyphens, underscores, colons, periods)
             let start = i;
@@ -543,6 +554,19 @@ mod tests {
         assert_eq!(tokens, vec!["<sample-widget_anchor>"]);
     }
 
+    #[test]
+    fn test_tokenize_inline_equation_is_atomic() {
+        let tokens = tokenize_mixed("is $t = 12.4 \"hour\"$ for");
+        assert_eq!(tokens, vec!["is", " ", "$t = 12.4 \"hour\"$", " ", "for"]);
+    }
+
+    #[test]
+    fn test_tokenize_escaped_dollar_is_not_equation() {
+        let tokens = tokenize_mixed("\\$5 and $x$");
+        assert!(tokens.contains(&"$x$"));
+        assert!(!tokens.iter().any(|t| t.starts_with("$5")));
+    }
+
     #[test]
     fn test_tokenize_cjk_char_level() {
         // CJK characters should be tokenized individually (no whitespace boundaries).