feat: adds subdirectory agent md files

[marissahuysentruyt]

Description

⚠️ NICE-TO-HAVE PARALLEL MERGE ⚠️
Can be merged directly into feat-agnostic-ai-folder-stuff before or after the washing machine skills PR #6127 or the skills mindset PR #6139

Adds scoped AGENTS.md files under 1st-gen/ and 2nd-gen/ so coding agents (and/or humans) get short, navigational context before diving into code. Each file is intentionally an index: a brief generation/package role, a small directory structure sketch, “where to look next” links to child AGENTS.md files or migration docs - not a full duplicate of CONTRIBUTOR-DOCS.

New files

Path	Role
1st-gen/AGENTS.md	Past vs future, migration-only changes, link to packages/tools/projects + 2nd-gen
1st-gen/packages/AGENTS.md	Component vs tool packages layout, link back to parent + tools/
1st-gen/tools/AGENTS.md	Shared tooling bucket
1st-gen/projects/AGENTS.md	Non-component workspaces
2nd-gen/AGENTS.md	Core vs swc split, build order, links into packages
2nd-gen/packages/core/AGENTS.md	Core package: bases, types, what does not belong
2nd-gen/packages/swc/AGENTS.md	SWC package: rendering, CSS, stories, tests, what does not belong

Motivation and context

Repo-root AGENTS.md points agents at .ai/, but 1st-gen vs 2nd-gen structure and "core vs swc" boundaries are easy to get wrong without local breadcrumbs. These new files give agents the right mental model in the directory they’re editing and link outward instead of duplicating long guides.

Related issue(s)

• fixes swc-1893

Screenshots (if appropriate)

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Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

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Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

1. Confirm relative links resolve properly

• From repo root, open AGENTS.md, then follow into 2nd-gen/AGENTS.md.
• Continue to follow links into packages/core/AGENTS.md or packages/swc/AGENTS.md
• Repeat from 1st-gen/AGENTS.md. Go topackages/AGENTS.md, tools/AGENTS.md, projects/AGENTS.md.

2. Confirm statements match current architecture (package counts, core-before-swc build order, “no new features in 1st-gen” policy).

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

Accessibility testing checklist

Required: Complete each applicable item and document your testing steps (replace the placeholders with your component-specific instructions).

Accessibility testing checklist

• Keyboard
  Documentation only.

• Screen reader
  Documentation only.

[changeset-bot]

⚠️ No Changeset found

Latest commit: dc3bf33

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[github-actions]

📚 Branch Preview Links

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• Storybook (second-gen)

🔍 First Generation Visual Regression Test Results

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

Deployed to Azure Blob Storage: pr-6137

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.