fix: protect special characters in math from markdown table parsers (#1462)

[hugogu]

Change Summary

Wiki.js uses markdown-it-attrs which interprets curly braces inside inline math ($...$) as attribute directives, stripping them from the formula. Additionally, markdown table parsers split cells at both | and & characters, breaking formulas containing those symbols.

This fix replaces {, }, |, and & inside math expressions with Unicode Private Use Area placeholders during markdown parsing, then restores them before passing to KaTeX/MathJax for rendering.

• <E000> / <E001>: temporary replacements for { / }
• <E002>: temporary replacement for | (table cell delimiter)
• <E003>: temporary replacement for & (table cell delimiter in multiline tables, used by LaTeX cases/arrays)

The placeholder approach was chosen over HTML escaping because it preserves LaTeX environments like \begin{array} that were broken by the previous {{}} escaping method.

Fixes #1581
Fixes #1462

Test

# Issue #1462 Test Cases

# Latex测试

## 特殊函数

| 符号 | 含义 | 定义/示例 |
|------|------|----------|
| $\zeta(s)$ | 黎曼ζ函数 | $\zeta(2) = \frac{\pi^2}{6}$ |
| $\Gamma(x)$ | 伽马函数 | $\Gamma(n) = (n-1)!$ |
| $\Gamma(z)$ | 伽马函数（复数） | $\Gamma(z) = \int_0^{\infty} t^{z-1}e^{-t}dt$ |
| $B(x, y)$ | 贝塔函数 | $B(x,y) = \frac{\Gamma(x)\Gamma(y)}{\Gamma(x+y)}$ |
| $\psi(x)$ | 双伽马函数 | $\psi(x) = \frac{\Gamma'(x)}{\Gamma(x)}$ |
| $\mathrm{Heaviside}(x)$ | 海维赛德阶跃 | $H(x) = \begin{cases} 1 & x \geq 0 \\ 0 & x < 0 \end{cases}$ |
| $\delta(x)$ | 狄拉克δ函数 | $\int_{-\infty}^{\infty} \delta(x)dx = 1$ |
| $\mathrm{sinc}(x)$ | sinc函数 | $\mathrm{sinc}(x) = \frac{\sin x}{x}$ |
| $\mathrm{rect}(x)$ | 矩形函数 | $\mathrm{rect}(x) = \begin{cases} 1 & |x| \leq 1/2 \\ 0 & \text{其他} \end{cases}$ |
| $\sigma_x, \sigma_y, \sigma_z$ | 泡利矩阵 | $\sigma_x = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$ |
| $\mathfrak{c}$ | 连续统基数 | $|\mathbb{R}| = \mathfrak{c}$ |
| $\sum_{n \in S}$ | 对集合求和 | $\sum_{n \in \mathbb{N}} \frac{1}{n^2}$ |

## Array Environment

$\begin{array}{lrc} 1 & 2 & 3 \\ 4 & 5 & 6 \end{array}$

text $\begin{array}{lrc} 1 & 2 & 3 \\ 4 & 5 & 6 \end{array}$ text

## Simple Fractions

$\frac{1}{3}$

text $\frac{1}{3}$ text

## Fractions with Superscripts

$\frac{1^{2}}{3^{4}}$

$\frac{1}{3^{4}}$

$\frac{1^{2}}{3}$

## Einstein Field Equation

$G_{\mu\nu} + \Lambda g_{\mu\nu} = \frac{8\pi G}{c^4} T_{\mu\nu}$

## Block Array

$$
\begin{array}{lrc}
1 & 2 & 3 \\
4 & 5 & 6
\end{array}
$$

The latest build by now (2.5.314) render it as

and

After the fix all latex text will be rendered correctly:

and

[vaagee]

Hi hugogu, thx for the PR! I implement it and it indeed solves the problem! But I found it also breaks the math rendering in preview. Now I can only see a bunch of latex syntex in preview, which makes latex debugging impossible until 'save and render'.
Do you have an idea how to make the rendering work again in preview?

[hugogu]

Hi hugogu, thx for the PR! I implement it and it indeed solves the problem! But I found it also breaks the math rendering in preview. Now I can only see a bunch of latex syntex in preview, which makes latex debugging impossible until 'save and render'. Do you have an idea how to make the rendering work again in preview?

Hi vaagee, I think the fix also works for the preview pane, I'll check it up later.

[vaagee]

Hi hugogu, thx for the PR! I implement it and it indeed solves the problem! But I found it also breaks the math rendering in preview. Now I can only see a bunch of latex syntex in preview, which makes latex debugging impossible until 'save and render'. Do you have an idea how to make the rendering work again in preview?

Hi vaagee, I think the fix also works for the preview pane, I'll check it up later.

HI hugogu, no worries. It's my own problem. The function "restoreBraces" was somehow lost when merging your code to mine, leading to the rendering bugs.