MUI to BUI migration

Support two paths through the migration: run the published recipe (@backstage/mui4-to-bui-migration-recipe) and finish its leftovers, or migrate directly using the standalone guidance. Both paths include verification.

Workflow

1. Choose the path and target

Honor a path the user already specified. Otherwise, ask in plain language:

Would you like to run the codemod and then finish its leftovers, or migrate directly with the standalone guidance? I recommend the codemod because it handles mechanical changes deterministically and can reduce agent token usage.

Use ordinary conversation so the choice works across agents. Wait for the answer before migration edits or recipe commands; a recommendation is not a selection. For an unattended run, require the request to specify the path.