ember-cli-update interrupted upgrade leaves half-applied files and no rollback path

Ember projects are typically upgraded with ember-cli-update, which offers a dry-run preview and an interactive mode that pauses whenever a file such as ember-cli-build.js conflicts with the incoming blueprint. The prompt shows old and new content side by side and leaves the merge decision entirely to the developer.

The open question is what the tool guarantees if an upgrade is abandoned partway through. There is no built-in rollback flag, so files touched before the interruption stay in a partially applied state, and new dependency entries in package.json can end up mismatched with node_modules when the install step never completes. Manual conflict resolution also risks dropping addon imports, which would only surface as missing modules at runtime. Recovery appears to rest entirely on external version control rather than on the tool itself.

1. What is the supported way to restore a project after an interrupted ember-cli-update run?
2. Does the tool document any expectations about repository state before upgrading, or is clean recovery purely a version-control concern?
3. Are the conflict prompts stable enough for scripted handling across releases, or should they be treated as interactive-only?