fix(dev): Gatsby HMR fails with ENOENT for missing node_modules files

[jimmyandrade]

Summary

Local gatsby develop / HMR stops serving a working app. The browser console reports:

[HMR] connected
[HMR] bundle has 26 errors

followed by many Webpack Module build failed: Error: ENOENT: no such file or directory, open '…/node_modules/…' errors, including:

• @hot-loader/react-dom/node_modules/scheduler/…
• axios/lib/defaults.js
• gatsby-link/index.js
• gatsby-react-router-scroll/index.js
• many gatsby/node_modules/@babel/runtime/helpers/** files

Likely cause

Corrupted or incomplete node_modules (often while gatsby develop is still running), plus npm hoisting that left gatsby-link / gatsby-react-router-scroll only nested under gatsby (develop SSR cannot resolve them from .cache).

Acceptance criteria

• Document recovery steps in TROUBLESHOOTING.md
• Clean reinstall restores a working module tree
• npm run develop on Node 18 serves without the 26 HMR ENOENT errors
• Site loads at http://localhost:8001 (verified HTTP 200)
• Durable deps: hoist gatsby-link / gatsby-react-router-scroll; override remark-mdx@1.6.22; ensure google-fonts dirs plugin

Resolution

Shipped in #452.

[jimmyandrade]

Fixed in #452: clean reinstall + direct gatsby-link / gatsby-react-router-scroll deps, remark-mdx@1.6.22 override, plugins/ensure-google-fonts-dirs, and TROUBLESHOOTING recovery steps. Local develop serves HTTP 200 on :8001.