Scenario: without this patch, if you fail a build, fix the code, let the thin build succeed, and then refresh the browser... then after reloading the browser page, it gets stuck on the "One sec" loader because the devserver status never clears the earlier BuildError.
- mark build status ready after sending hot patch messages so refreshes succeed
- reuse the same helper from reload command to avoid stale loading screens
- add set_ready() helper to avoid duplicate status broadcasts
