Preserve live API additions when replacing a shared runtime image

When a shared service has live API additions from an unmerged branch, a newer image built from the target branch can silently remove those routes while passing health checks. Before replacing that runtime, reconcile its source with the live API contract and test authenticated reads used by dependent clients. To recover without reverting unrelated worker improvements, rebase the API additions onto current source and overlay only the changed API module onto the current immutable runtime. This requires compatible module dependencies; deployment success alone does not prove the recovered client flow.

Applies when: Multiple branches release changes to the same shared backend service. Keywords: unmerged branch missing endpoint image replacement health check contract