Advance Docs Agent drift audit contract

[chubes4]

Summary

• advance the pinned Docs Agent reusable workflow and CI producer checkout to merge 21dbeeddea7ae29efa68bb1c0590a00bbed93f3d from Require drift audit before maintenance no-op docs-agent#161
• advance the independently verified native package provenance assertion to 85443eb91c12b2759d8e207f1ae4421407b4cc5e
• retain WP Codebox v0.12.27 / 65cc5fb4699cb7c2df13d04b4715c97097ac7565

This enables the bounded source-vs-document drift audit before technical maintenance can return no_changes.

How to test

1. Check out Docs Agent at 21dbeeddea7ae29efa68bb1c0590a00bbed93f3d.
2. Check out WP Codebox at 65cc5fb4699cb7c2df13d04b4715c97097ac7565.
3. Run pnpm install --frozen-lockfile.
4. Run DOCS_AGENT_DIR=/path/to/docs-agent WP_CODEBOX_DIR=/path/to/wp-codebox pnpm test.
5. Run pnpm build && pnpm verify.
6. Run actionlint .github/workflows/*.yml.
7. Run git diff --check origin/trunk...HEAD.

All commands pass locally.

Compatibility

No extension-path or backwards-compatibility impact. This advances immutable producer revisions without changing the Build with WordPress workflow inputs, writable paths, WP Codebox version, or generated plugin outputs.

Source relationships

• Require source-vs-document drift audit before maintenance no-op docs-agent#160
• Require drift audit before maintenance no-op docs-agent#161

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode with OpenAI GPT-5.6 Sol
• Used for: Updated the immutable producer pins, verified the complete consumer contract, and drafted this PR description. Chris reviewed and owns the change.