Advance Docs Agent to WP Codebox v0.12.26

[chubes4]

Summary

• advance the reusable Docs Agent workflow and validation checkout to WP Codebox v0.12.26
• record immutable release commit and published asset digests
• declare the restored .codebox runtime-control exclusion added by Exclude Codebox control files from publication snapshots wp-codebox#1848

Why

Build with WordPress acceptance run https://github.com/Automattic/build-with-wordpress/actions/runs/29627878516 proved the v0.12.25 dependency-artifact fix, then exposed mutable .codebox state entering publication integrity snapshots. WP Codebox v0.12.26 fixes that release regression.

How to test

1. Check out WP Codebox at tag v0.12.26.
2. Run php tests/validate-docs-agent-packages.php.
3. Run php tests/validate-external-native-package-sources.php.
4. Run WP_CODEBOX_DIR=/path/to/wp-codebox php tests/validate-wp-codebox-run-agent-task-contract.php.
5. Run php tests/repair-docs-links-smoke.php.

Compatibility

• Existing reusable-workflow inputs and outputs are unchanged.
• Runtime-owned .codebox files are excluded from publication snapshots; Git-aware checks for publishable workspace files remain intact.

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI GPT-5.6 Sol via OpenCode
• Used for: Advanced immutable release pins and fixtures, documented the runtime-control exclusion, and ran verification with Chris reviewing and owning the change.