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/E509.md.
mfeflow

    MFEFLOW_E509

    Files of the target version are missing on the host.

    Fix

    Deploy that version again from its build, or pick another version with --to. The index was not changed. See https://mfeflow.github.io/mfeflow/guide/deploy-and-rollback.