desktop_notification: Fix bad rendering of math formulas.

Earlier, for the desktop notifications having latex math
like "$$1 \oplus 0 = 1$$, the notification had the math
included multiple times.

This commit fixes the incorrect behavior by replacing
the KaTeX with the raw LaTeX source.

Fixes #25289.

web/src/message_notifications.js

@@ -19,6 +19,7 @@ function get_notification_content(message) {
     // Convert the content to plain text, replacing emoji with their alt text
     const $content = $("<div>").html(message.content);
     ui_util.replace_emoji_with_text($content);
+    ui_util.change_katex_to_raw_latex($content);
     spoilers.hide_spoilers_in_notification($content);
 
     if (

web/src/ui_util.ts

@@ -30,6 +30,20 @@ export function replace_emoji_with_text($element: JQuery): void {
     });
 }
 
+export function change_katex_to_raw_latex($element: JQuery): void {
+    // Find all the span elements with the class "katex"
+    $element.find("span.katex").each(function () {
+        // Find the text within the <annotation> tag
+        const latex_text = $(this).find('annotation[encoding="application/x-tex"]').text();
+
+        // Create a new <span> element with the raw latex wrapped in $$
+        const $latex_span = $("<span>").text("$$" + latex_text + "$$");
+
+        // Replace the current .katex element with the new <span> containing the text
+        $(this).replaceWith($latex_span);
+    });
+}
+
 export function blur_active_element(): void {
     // this blurs anything that may perhaps be actively focused on.
     if (document.activeElement instanceof HTMLElement) {

web/tests/notifications.test.js

@@ -340,6 +340,7 @@ test("message_is_notifiable", () => {
 
 test("basic_notifications", () => {
     $("<div>").set_find_results(".emoji", {replaceWith() {}});
+    $("<div>").set_find_results("span.katex", {each() {}});
 
     let n; // Object for storing all notification data for assertions.
     let last_closed_message_id = null;