client/src/marp/render.ts

import { Marp } from '@marp-team/marp-core'

// One reusable Marp instance. inlineSVG is disabled so the rendered output is a
// predictable `<div class="marpit"><section>…</section>…</div>` structure that we
// can slice into a single-slide stage and a thumbnail rail.
const marp = new Marp({ inlineSVG: false })

export interface RenderResult {
  html: string
  css: string
  count: number
}

export function renderMarp(markdown: string): RenderResult {
  const { html, css } = marp.render(markdown)
  const count = (html.match(/<section[\s>]/g) || []).length
  return { html, css, count }
}