fix(dom): mask AX password values per UTF-16 code unit

Count UTF-16 code units when masking password values to match Chromium.
Cover initial and live values across ASCII, BMP, supplementary characters,
combining sequences, ZWJ emoji, and empty passwords, verified against
Chromium 145 in 14 cases.

moli-dom/src/accessibility/ax_properties.rs

@@ -403,9 +403,10 @@ pub(super) fn ax_value(document: &NativeDom, node_id: NodeId, node: &Node) -> Op
                     | InputType::Submit
             ) =>
         {
-            // Chromium exposes a password value only as one bullet per character.
+            // Chromium exposes a password value as one bullet per UTF-16 code unit.
             if element.input_type() == InputType::Password {
-                "\u{2022}".repeat(element.input_value().chars().count())
+                let value = element.input_value();
+                "\u{2022}".repeat(value.encode_utf16().count())
             } else {
                 element.input_value()
             }
@@ -939,22 +940,48 @@ mod tests {
     }
 
     #[test]
-    fn password_value_is_exposed_as_bullets_only() {
-        let (mut document, root) = document_with_root();
-        let input = document.create_element("input");
-        assert!(document.set_attribute(input, "type", "password"));
-        assert!(document.set_attribute(input, "value", "secret"));
-        assert!(document.append_child(root, input));
+    fn password_value_is_masked_per_utf16_code_unit() {
+        // Chromium's Accessibility.getFullAXTree masks both initial and live values.
+        for (password, bullet_count) in [
+            ("secret", 6),
+            ("密码", 2),
+            ("😀", 2),
+            ("a😀密", 4),
+            ("e\u{301}", 2),
+            ("👩\u{200d}💻", 5),
+            ("", 0),
+        ] {
+            for live_value in [false, true] {
+                let (mut document, root) = document_with_root();
+                let input = document.create_element("input");
+                assert!(document.set_attribute(input, "type", "password"));
+                assert!(document.append_child(root, input));
+                if live_value {
+                    assert!(document.set_attribute(input, "value", "initial"));
+                    let element = document
+                        .node_mut(input)
+                        .expect("password input")
+                        .data_mut()
+                        .as_element_mut()
+                        .expect("password input element");
+                    assert!(element.set_input_value(password));
+                } else {
+                    assert!(document.set_attribute(input, "value", password));
+                }
 
-        let value = ax_value(
-            &document,
-            input,
-            document.node(input).expect("password input"),
-        )
-        .expect("password input has an AX value");
-        assert_eq!(
-            value["value"],
-            "\u{2022}\u{2022}\u{2022}\u{2022}\u{2022}\u{2022}"
-        );
+                let value = ax_value(
+                    &document,
+                    input,
+                    document.node(input).expect("password input"),
+                );
+                let expected = (bullet_count > 0).then(|| {
+                    json!({
+                        "type": "string",
+                        "value": "\u{2022}".repeat(bullet_count),
+                    })
+                });
+                assert_eq!(value, expected, "password={password:?}, live={live_value}");
+            }
+        }
     }
 }