Document Figma handoff diagnostics

[chubes4]

Summary

• document the Figma source payload, deterministic debug summary, Studio request/response contract, and correlated failure logging
• retain the hosted Docs Agent index update while completing its reviewer-insufficient output from source evidence
• mark the bounded PR Improve Figma Studio handoff diagnostics #100 documentation drift as satisfied and move future publication off the branch affected by WP Codebox #1894

Replaces #129.

How to test

1. Run pnpm install --frozen-lockfile.
2. Run pnpm test.
3. Run pnpm build.
4. Run pnpm verify.
5. Check out Docs Agent 7b67d341eea16b75b8e055507d36a8d8e69a1fe3 and WP Codebox a6fe2d208e990a8d04104aa74aacbb8d1539fbc1.
6. Run DOCS_AGENT_DIR=/path/to/docs-agent WP_CODEBOX_DIR=/path/to/wp-codebox pnpm test.
7. Run actionlint .github/workflows/*.yml and git diff --check.

Hosted deterministic execution proof: https://github.com/Automattic/build-with-wordpress/actions/runs/29745216730

Compatibility

Documentation and workflow policy only. Generated plugins and runtime APIs are unchanged. The publication branch changes because stale post-squash branch reuse is tracked in Automattic/wp-codebox#1894.

AI assistance

• AI assistance: Yes
• Tool(s): Native Docs Agent with OpenAI GPT-5.5; OpenCode with GPT-5.6-sol
• Used for: The hosted Docs Agent drafted the index update; OpenCode reviewed it against source, completed the payload and diagnostics documentation, updated lifecycle policy, and verified the result with Chris reviewing and owning the change.