Closes #1767

Summary

• Materialize policy-authorized immutable public runtime source trees under a private OS temp root, outside the target workspace and artifacts directory.
• Support Git-pinned component, provider-plugin, and bundled-library sources plus HTTPS ZIP artifacts for component/provider roles.
• Authorize exact ZIP URLs independently in EXTERNAL_PACKAGE_SOURCE_POLICY; policy entries can pin the expected SHA-256 separately from caller descriptors.
• Verify HTTPS transport, exact allowlisting, same-host allowlisted redirects, bounded transfer/extraction, digest-before-extract, one archive root, and ZIP traversal/symlink/special-file/encryption/ZIP64/bomb defenses.
• Lower sources through existing component/provider/overlay primitives and preserve only compact provenance in uploaded artifacts.
• Remove private sources after execution, validation failure, process exit, and termination signals.

Compatibility

• Adds optional runtime_sources HTTPS ZIP descriptors; existing reusable-workflow callers and Git source descriptors remain unchanged.
• Extends the operator-controlled EXTERNAL_PACKAGE_SOURCE_POLICY v1 schema with optional runtime_artifacts; callers cannot self-authorize artifact URLs or expected digests.

Verified Playground Integration

The CI integration uses only a dummy OPENAI_API_KEY and makes no provider request:

• Agents API: automattic/agents-api@59d1e6b473f22498e40e279130bbb4f9bcde3b73
• OpenAI provider: https://downloads.wordpress.org/plugin/ai-provider-for-openai.1.0.3.zip with SHA-256 48f3c0c714b3164cda79d320829830d5a0ea1116e0b19653da8af898a22d3bb6 and archive root ai-provider-for-openai
• PHP AI Client: wordpress/php-ai-client@631704201d15ffeff7091ad3bc7156db74054956
• Confirmed WordPress boot, canonical flat agent import using exact slug flat-runtime-agent, Agents API registry, active and registered OpenAI provider, and initialized PHP AI Client.
• Confirmed private materialization cleanup and upload staging strips private paths while retaining source provenance.

How to test

1. Run npm run build.
2. Run npm run test:runtime-sources-materialization.
3. Run WP_CODEBOX_RUN_NETWORK_INTEGRATION=1 npm run test:runtime-sources-playground-integration.
4. Run npm run test:agent-task-contracts.
5. Run npm run test:production-boundary-enforcement.
6. Run npm run test:runtime-tool-policy.
7. Run actionlint .github/workflows/run-agent-task.yml .github/workflows/agent-task-contracts.yml.

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI gpt-5.6-terra and OpenCode
• Used for: Implemented and verified immutable runtime-source ZIP materialization, security controls, upload provenance handling, and the real Playground integration with Chris Huber.