Use deterministic Docs Agent completion

[chubes4]

Summary

• pin Docs Agent 7b67d341, which generates completion artifacts from host-observed facts
• remove model response formatting from the effective acceptance path without changing maintenance or bootstrap inputs

How to test

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

Compatibility

The completion artifact is now host-generated and its v1 shape contains machine-observed facts only. Consumer inputs, writable paths, and bootstrap criteria are unchanged.

Depends on Automattic/docs-agent#176

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode with GPT-5.6-sol
• Used for: Updated immutable producer provenance and assertions with Chris reviewing and owning the change.