Function detect_duplication 

pub fn detect_duplication(
    options: &DuplicationOptions,
) -> Result<Value, ProgrammaticError>

Run duplication analysis and return the JSON output contract.

This is the first runtime path owned by fallow-api instead of the CLI crate. It intentionally returns the same root JSON shape that embedders already receive from fallow-node.

Errors

Returns a structured programmatic error for invalid options, config load failures, git changed-file failures, or serialization failures.