Use WP Codebox v0.12.10 release

[chubes4]

Summary

• Advance the reusable workflow and validation producer pin to WP Codebox v0.12.10.
• Record regression run 29305012941 and document private runtime-path sanitization.
• Validate the producer sanitizer, regression fixture, and provenance boundary.

Testing

1. php tests/validate-docs-agent-bundle.php
2. php tests/validate-external-native-package-sources.php
3. WP_CODEBOX_DIR=<v0.12.10 checkout> php tests/validate-wp-codebox-run-agent-task-contract.php
4. php tests/repair-docs-links-smoke.php
5. AGENTS_API_DIR=<Agents API checkout> php tests/native-agent-import.php
6. actionlint .github/workflows/*.yml
7. git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI gpt-5.6-terra via OpenCode
• Used for: Updated the release pin, regression contract assertions, documentation, and validation with Chris Huber.