For AI agents: the complete documentation index is available at https://mfeflow.github.io/mfeflow/llms.txt, the full documentation bundle is available at https://mfeflow.github.io/mfeflow/llms-full.txt, and this page is available as Markdown at https://mfeflow.github.io/mfeflow/errors/E603.md.
mfeflow

    MFEFLOW_E603

    A feature migration could not be loaded or failed.

    Fix

    Nothing was written. Update mfeflow to a build that ships the migration, or report the feature and versions named above.