Generate completion reports deterministically

[chubes4]

Summary

• generate the completion artifact from caller inputs, Git state, writable scope, and bootstrap filesystem checks
• remove model-authored completion JSON and transcript parsing from the acceptance path
• retain only machine-observed report facts and harden canonical artifact staging against traversal, symlinks, and oversized output

Fixes #174

How to test

1. Run php tests/validate-docs-agent-packages.php.
2. Run php tests/validate-docs-agent-completion-contract.php.
3. Check out WP Codebox at a6fe2d208e990a8d04104aa74aacbb8d1539fbc1, then run WP_CODEBOX_DIR=/path/to/wp-codebox php tests/validate-wp-codebox-run-agent-task-contract.php.
4. Run php tests/validate-external-native-package-sources.php.
5. Run actionlint .github/workflows/*.yml and git diff --check.

Compatibility

This intentionally removes the unstable model-authored DOCS_AGENT_COMPLETION_REPORT response contract and revises docs-agent/completion-report/v1 to contain host-observed facts only. Accepted consumers will be repinned atomically; no backwards-compatibility parser is included.

Control-plane evidence

Homeboy Lab finalization was attempted but blocked before provider execution by Extra-Chill/homeboy#9115. Direct PR finalization was explicitly authorized after the committed candidate passed the checks above.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode with GPT-5.6-sol
• Used for: Implemented and reviewed the deterministic completion contract, schema, workflow integration, documentation, and tests with Chris reviewing and owning the change.