`pnpm docs:dev` rendered a blank page with `does not provide an
export named 'default'` thrown from dayjs.min.js. Mermaid 11 ships
its `dayjs`, `cytoscape`, `debug` and `@braintree/sanitize-url`
dependencies with a CommonJS `main` field but no `default` ESM
export. Vite's dev server resolves those modules eagerly as ESM
and the browser throws on the first navigation.
The production build (`docs:build`) was unaffected — Rollup's
plugin pipeline already applies the CJS→ESM interop wrapper. This
fix is exclusively for the dev happy path: `optimizeDeps.include`
forces Vite to pre-bundle the Mermaid dependency tree, which
applies the same interop shim at dev-server boot.
Caught by manual smoke of the merged docs-site chantier — the
build-time Mermaid-rendering fence in `.gitea/workflows/docs-site.yml`
didn't catch this because it only inspects production HTML.
Julien Gautier