The `website` prebuild (`optimize-images.mjs` + `sync:sponsors`) downloads avatars, out-sourced static assets and the sponsors SVG from GitHub. The cloud-hosted Claude Code sandbox (claude.ai/code) blocks those outbound calls, so the whole `pnpm --filter website build` aborts before `docusaurus build` can even run — preventing MDX content from being validated in that environment. Gate every remote fetch on `process.env.CLAUDE_CODE_REMOTE === 'true'`: when set (cloud Claude Code only), write small placeholder files at the expected output paths instead of calling the network. Local Claude Code CLI, developer machines and CI are unaffected — `CLAUDE_CODE_REMOTE` is not set there, so the original fetch-and-SHA1-verify path still runs byte-for-byte. The local MDX validation in `assessMissingSocialImage()` is preserved unchanged in both modes. Also inline the former `sync:sponsors` bash one-liner into `optimize-images.mjs` so a single env-var gate covers all remote fetching and the build pipeline has one fewer hop. https://claude.ai/code/session_01GfRHx2CMQy1iXJAS27HAyk Co-authored-by: Claude <noreply@anthropic.com>