From 360b755210d6e364c3d63a9bbad666f441401a6a Mon Sep 17 00:00:00 2001
From: Simone Checchia <62959575+simonechecchia@users.noreply.github.com>
Date: Wed, 8 Jul 2026 21:06:56 +0200
Subject: [PATCH] fix(app): render \[...\] LaTeX display math delimiters

Fixes #24426
---
 packages/ui/src/context/marked.test.ts | 84 ++++++++++++++++++++++++++
 packages/ui/src/context/marked.tsx     | 16 ++---
 2 files changed, 93 insertions(+), 7 deletions(-)
 create mode 100644 packages/ui/src/context/marked.test.ts

diff --git a/packages/ui/src/context/marked.test.ts b/packages/ui/src/context/marked.test.ts
new file mode 100644
index 000000000000..1e43de1a752f
--- /dev/null
+++ b/packages/ui/src/context/marked.test.ts
@@ -0,0 +1,84 @@
+import { describe, expect, test } from "bun:test"
+import { marked } from "marked"
+import { katexExtension, renderMathInText } from "./marked"
+
+describe("renderMathInText (native markdown parser path)", () => {
+  test("renders \\(...\\) inline math", () => {
+    const html = renderMathInText("A quantum state \\( \\rho \\) is normalized.")
+    expect(html).toContain("katex")
+    expect(html).not.toContain("\\(")
+    expect(html).not.toContain("\\)")
+  })
+
+  test("renders \\[...\\] display math", () => {
+    const html = renderMathInText("\\[\n\\langle O \\rangle = \\mathrm{Tr}(O\\rho)\n\\]")
+    expect(html).toContain("katex")
+    expect(html).toContain('class="katex-display"')
+    expect(html).not.toContain("\\[")
+    expect(html).not.toContain("\\]")
+  })
+
+  test("still renders $$...$$ display math", () => {
+    const html = renderMathInText("$$\nx^2\n$$")
+    expect(html).toContain("katex")
+    expect(html).toContain('class="katex-display"')
+  })
+})
+
+describe("katexExtension (marked tokenizer path)", () => {
+  const parser = marked.use(katexExtension)
+
+  test("renders \\(...\\) inline math", async () => {
+    const html = await parser.parse("A quantum state \\( \\rho \\) is normalized.")
+    expect(html).toContain("katex")
+    expect(html).not.toContain("\\(")
+  })
+
+  test("renders \\[...\\] display math on its own lines", async () => {
+    const html = await parser.parse("\\[\n\\langle O \\rangle = \\mathrm{Tr}(O\\rho)\n\\]")
+    expect(html).toContain("katex")
+    expect(html).toContain('class="katex-display"')
+  })
+
+  test("still renders $$...$$ display math", async () => {
+    const html = await parser.parse("$$\nx^2\n$$")
+    expect(html).toContain("katex")
+    expect(html).toContain('class="katex-display"')
+  })
+
+  test("does not mangle fenced code blocks containing backslash-bracket text", async () => {
+    const html = await parser.parse("```\n\\[ not math \\]\n```")
+    expect(html).toContain("\\[ not math \\]")
+    expect(html).not.toContain("katex")
+  })
+
+  test("renders \\(...\\) inside a markdown table cell without CommonMark eating the backslash", async () => {
+    const md = [
+      "| Fratto semplice | Antitrasformata |",
+      "|---|---|",
+      "| \\(\\frac{1}{s+a}\\) | \\(e^{-at}\\text{sca}(t)\\) |",
+    ].join("\n")
+    const html = await parser.parse(md)
+    expect(html).toContain("katex")
+    expect(html).not.toContain("\\(")
+    expect(html).not.toContain("\\)")
+  })
+})
+
+describe("issue #24426 repro", () => {
+  test("full snippet renders both delimiter styles without leaking raw LaTeX", () => {
+    const input = [
+      "A quantum state \\( \\rho \\) gives an observable expectation by",
+      "",
+      "\\[",
+      "\\langle O \\rangle = \\mathrm{Tr}(O\\rho)",
+      "\\]",
+    ].join("\n")
+
+    const html = renderMathInText(input)
+    expect(html).not.toContain("\\(")
+    expect(html).not.toContain("\\)")
+    expect(html).not.toContain("\\[")
+    expect(html).not.toContain("\\]")
+  })
+})
diff --git a/packages/ui/src/context/marked.tsx b/packages/ui/src/context/marked.tsx
index a4f264ac6720..abbde1006830 100644
--- a/packages/ui/src/context/marked.tsx
+++ b/packages/ui/src/context/marked.tsx
@@ -378,19 +378,20 @@ export const OpenCodeTheme = {
 
 registerCustomTheme("OpenCode", () => Promise.resolve(OpenCodeTheme))
 
-function renderMathInText(text: string): string {
+export function renderMathInText(text: string): string {
   let result = text
 
-  // Display math: $$...$$
-  const displayMathRegex = /\$\$([\s\S]*?)\$\$/g
-  result = result.replace(displayMathRegex, (_, math) => {
+  // Display math: $$...$$ or \[...\]
+  const displayMathRegex = /\$\$([\s\S]*?)\$\$|\\\[([\s\S]*?)\\\]/g
+  result = result.replace(displayMathRegex, (match, dollarMath, bracketMath) => {
+    const math = dollarMath ?? bracketMath
     try {
       return katex.renderToString(math, {
         displayMode: true,
         throwOnError: false,
       })
     } catch {
-      return `$$${math}$$`
+      return match
     }
   })
 
@@ -412,8 +413,9 @@ function renderMathInText(text: string): string {
 
 const inlineMathRegex = /^\\\(((?:\\.|[^\\\n])*?)\\\)/
 const blockMathRegex = /^\$\$\n([\s\S]+?)\n\$\$(?:\n|$)/
+const blockMathBracketRegex = /^\\\[\n([\s\S]+?)\n\\\](?:\n|$)/
 
-const katexExtension: MarkedExtension = {
+export const katexExtension: MarkedExtension = {
   extensions: [
     {
       name: "inlineKatex",
@@ -439,7 +441,7 @@ const katexExtension: MarkedExtension = {
       name: "blockKatex",
       level: "block",
       tokenizer(src) {
-        const match = src.match(blockMathRegex)
+        const match = src.match(blockMathRegex) ?? src.match(blockMathBracketRegex)
         if (!match) return
         return {
           type: "blockKatex",