From 33d8320ce8c26948aeefe4bbc3c4c247cc939179 Mon Sep 17 00:00:00 2001
From: Vivek Dubey <viveksantoshkumardubey@gmail.com>
Date: Wed, 6 May 2026 16:44:34 +0530
Subject: [PATCH] fix: normalize double-escaped LaTeX backslashes and HTML
 entities (#14564)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Fixes #14562

## Problem
LLMs like DeepSeek V4 Flash and Qwen3-MAX return \\( and \\[
(double backslash) in LaTeX output. The preprocessLaTeX() function
only handled single backslash delimiters, so equations showed as raw
text.
HTML entities like &lt; and &gt; were also not decoded.

## Solution
Added normalization step before existing delimiter conversion:
- \\( → \(  and  \\[ → \[
- &lt; → <  and  &gt; → >  and  &amp; → &

---------

Co-authored-by: Vivek <viveksantoshkumardubey@email.com>
---
 web/src/utils/chat.ts            | 13 ++++++++++++-
 web/src/utils/tests/chat.test.ts | 26 ++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 web/src/utils/tests/chat.test.ts

diff --git a/web/src/utils/chat.ts b/web/src/utils/chat.ts
index cc0024950..879289d3b 100644
--- a/web/src/utils/chat.ts
+++ b/web/src/utils/chat.ts
@@ -56,14 +56,25 @@ const BLOCK_MATH_RE = /\\\[([\s\S]*?)(?<![a-zA-Z])\\\]/g;
 const INLINE_MATH_RE = /\\\(([\s\S]*?)(?<![a-zA-Z])\\\)/g;
 
 export const preprocessLaTeX = (content: string) => {
-  const blockProcessedContent = content.replace(
+  const normalizedContent = content
+    .replace(/\\\\\[/g, '\\[')
+    .replace(/\\\\\(/g, '\\(')
+    .replace(/\\\\\]/g, '\\]')
+    .replace(/\\\\\)/g, '\\)')
+    .replace(/&lt;/g, '<')
+    .replace(/&gt;/g, '>')
+    .replace(/&amp;/g, '&');
+
+  const blockProcessedContent = normalizedContent.replace(
     BLOCK_MATH_RE,
     (_, equation) => `$$${equation}$$`,
   );
+
   const inlineProcessedContent = blockProcessedContent.replace(
     INLINE_MATH_RE,
     (_, equation) => `$${equation}$`,
   );
+
   return inlineProcessedContent;
 };
 
diff --git a/web/src/utils/tests/chat.test.ts b/web/src/utils/tests/chat.test.ts
new file mode 100644
index 000000000..82b478071
--- /dev/null
+++ b/web/src/utils/tests/chat.test.ts
@@ -0,0 +1,26 @@
+import { preprocessLaTeX } from '../chat';
+
+test('handles double-escaped inline LaTeX', () => {
+  const result = preprocessLaTeX('\\\\(\\\\Delta = b^2\\\\)');
+  expect(result).toBe('$\\Delta = b^2$');
+});
+
+test('handles double-escaped block LaTeX', () => {
+  const result = preprocessLaTeX('\\\\[E = mc^2\\\\]');
+  expect(result).toBe('$$E = mc^2$$');
+});
+
+test('decodes HTML entities', () => {
+  const result = preprocessLaTeX('a &lt; b &amp; c &gt; d');
+  expect(result).toBe('a < b & c > d');
+});
+
+test('handles mixed double-escaped delimiters with HTML entities', () => {
+  const result = preprocessLaTeX('\\\\(x &lt; y\\\\)');
+  expect(result).toBe('$x < y$');
+});
+
+test('passes through already correct single-escaped delimiters unchanged', () => {
+  const result = preprocessLaTeX('\\(x = 1\\)');
+  expect(result).toBe('$x = 1$');
+});
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