Shiki warning: StorySourceCode creates a new highlighter on every mount

[earthabledev]

Describe the bug

Opening / switching stories with the Source panel active repeatedly creates new Shiki highlighter instances. After enough navigations the browser console warns:

[Shiki] 10 instances have been created. Shiki is supposed to be used as a singleton, consider refactoring your code to cache your highlighter instance; Or call `highlighter.dispose()` to release unused instances.

This is more noticeable in projects with many stories (e.g. browsing a large story tree), but it is not project-specific.

Root cause: @histoire/app StorySourceCode.vue calls createHighlighter() inside onMounted and neither reuses a shared instance nor calls dispose() on unmount:

https://github.com/histoire-dev/histoire/blob/main/packages/histoire-app/src/app/components/panel/StorySourceCode.vue#L89-L100

Shiki documents that highlighters should be singletons (warns every 10 instances). Related Shiki discussion: shikijs/shiki#756

Suggested fix: cache a module-level Promise<Highlighter> (same langs/themes) and reuse it across remounts. Optionally also share/dispose the Node-side highlighters created in packages/histoire/src/node/markdown.ts (createMarkdownRenderer is invoked from both the Vite markdown plugin and the markdown file watcher without reuse).

I do not plan to open a PR unless maintainers want one.

Reproduction

1. Open the Vue 3 Histoire starter: https://stackblitz.com/edit/histoire-vue3-starter
2. Run Histoire (pnpm run story:dev / the StackBlitz Histoire script).
3. Open any story so the Source panel is visible.
4. Switch between stories (or variants that remount the source panel) 10+ times.
5. Observe the Shiki singleton warning in the browser console.

No custom app code is required; the default starter is enough. The same path still exists on main as linked above.

System Info

  System:
    OS: macOS 26.5.2
    CPU: (10) arm64 Apple M1 Max
    Memory: 4.86 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.14.0 - …/bin/node
    npm: 11.9.0 - …/bin/npm
    pnpm: 10.30.3 - …/bin/pnpm
    bun: 1.3.11 - …/bin/bun
  Browsers:
    Chrome: 151.0.7922.71
    Edge: 150.0.4078.105
    Firefox: 152.0.6
    Safari: 26.5.2
  npmPackages:
    @histoire/plugin-vue: 1.0.0-beta.1 => 1.0.0-beta.1
    @vitejs/plugin-vue: ^6.0.8 => 6.0.8
    histoire: 1.0.0-beta.1 => 1.0.0-beta.1
    vite: ^8.1.5 => 8.1.5

Used Package Manager

pnpm

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Start a new pull request in StackBlitz Codeflow.

• histoire-vue3-starter (Open reproduction)