Problem

KaTeXs aligned/gatheredenvironments treat the entire block as one equation and only permit a single\tagper block (parse error "Multiple \tag"). When LLMs emit\tag{...}insidealigned` — as in:

$$
\boxed{\begin{aligned}
r_A E_\pi(k;0) &= B(k^2) \tag{10}\\
F_R(k;0) + 2r_A F_\pi(k;0) &= A(k^2) \tag{11}
\end{aligned}}
$$

KaTeX throws KaTeX parse error: Multiple \tag, which rehype-katex
renders as <span class="katex-error" style="color:#cc0000"> —
showing red error text in the web UI.

Fix

Instead of stripping \tag commands (which loses equation numbers),
convert the environments when \tag is present:

• \begin{aligned} → \begin{align}
• \begin{gathered} → \begin{gather}
• \begin{alignedat}{N} → \begin{alignat}{N}

KaTeX's align/gather/alignat support \tag on every row
natively. Plain aligned blocks without \tag are left unchanged
so they keep their un-numbered behaviour. The conversion is only
applied when \tag is detected in the math source.

if (/\\tag\*?\s*\{/.test(source)) {
  source = source
    .replace(/\\begin\{alignedat\}\{(\d+)\}/g, "\\begin{alignat}{$1}")
    .replace(/\\end\{alignedat\}/g, "\\end{alignat}")
    .replace(/\\begin\{aligned\}/g, "\\begin{align}")
    .replace(/\\end\{aligned\}/g, "\\end{align}")
    .replace(/\\begin\{gathered\}/g, "\\begin{gather}")
    .replace(/\\end\{gathered\}/g, "\\end{gather}");
}

Files changed

• desktop/frontend/src/components/latexNormalize.ts — aligned→align
  conversion when \tag is present
• desktop/frontend/src/__tests__/math-golden.test.ts — 6 new unit
  tests + 1 updated e2e test

Testing

All 99 golden tests pass (npx tsx src/__tests__/math-golden.test.ts).