docs: ESLint 10 upgrade investigation and compatibility analysis

[Copilot]

What

Comprehensive investigation into ESLint 10 upgrade feasibility. Created ESLINT-10-UPGRADE-INVESTIGATION.md documenting breaking changes, plugin compatibility matrix, and upgrade blockers.

Decision: Remain on ESLint 9.39.2 due to critical plugin incompatibilities.

Why

ESLint 10 released with breaking API changes. Investigation needed to assess upgrade path and breaking changes impact on the codebase.

How

Breaking Changes Analysis:

• Removed deprecated context methods (context.getFilename() → context.filename)
• eslint-env comments now errors (1 instance found: packages/react/jest.config.mjs)
• Node.js requirement >=24 ✓ met
• eslintrc removal ✓ not applicable (using flat config)

Plugin Compatibility:

• ❌ BLOCKER: eslint-plugin-react@7.37.5 - uses removed APIs
• ❌ BLOCKER: eslint-plugin-mdx@3.6.2 - uses removed APIs (104 MDX files affected)
• ⚠️ eslint-plugin-import@2.32.0, eslint-plugin-baseline-js@0.5.0 - unclear/explicit exclusion
• ✅ typescript-eslint, eslint-plugin-jest, eslint-plugin-perfectionist - compatible

Documentation includes:

• Breaking changes with migration paths
• Plugin compatibility status and error examples
• Package update requirements for future upgrade
• Monitoring links: eslint-plugin-react#3979, eslint-plugin-mdx#604

Checklist

• Add or update unit tests
• Add or update documentation
• Add or update stories
• Add or update exports in index.* files
• Start the PR title with a Conventional Commit prefix, as explained here.

Additional notes

No code changes made. Upgrade blocked until eslint-plugin-react and eslint-plugin-mdx release ESLint 10-compatible versions. When unblocked, upgrade requires 6 package updates and removing 1 eslint-env comment.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• eslint.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
• storybook.js.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/design-system/design-system/storybook/node_modules/.bin/../../../node_modules/.pnpm/storybook@10.2.7_@testing-library+dom@10.4.1_prettier@3.8.1_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/storybook/dist/bin/dispatcher.js build --output-dir dist/ --config-dir config/ --quiet (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/design-system/design-system/storybook/node_modules/.bin/../../../node_modules/.pnpm/storybook@10.2.7_@testing-library+dom@10.4.1_prettier@3.8.1_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/storybook/dist/bin/dispatcher.js build --output-dir dist/ --config-dir config/ --quiet user.name (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[VincentSmedinga]

Cool, let’s wait a bit until the packages we use have been made compatible with ESLint 10.