Create a test fixture and publish nightly Host artifact for integration testing

Prepare a test fixture which takes the nightly artifact of Host. The integration tests to validate the contract between Host and Workers will be written using this fixture. Also, publish the nightly artifact of Host to a feed.

Start by locating the existing integration-test fixtures and the workflow or packaging entry point that publishes Host artifacts. Trace how Workers consume test artifacts and how nightly builds publish to a feed. Done means a fixture can consume the nightly Host artifact and the artifact is available from the feed for Host–Workers contract tests.

Written by the indexing model from the issue text.