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/E123.md.
mfeflow

    MFEFLOW_E123

    This folder already has an mfeflow.json.

    Fix

    adopt only starts a project file; it never changes one. Use mfeflow add or mfeflow upgrade on this project, or run adopt in a folder that has no mfeflow.json.