Function backfill_sfx_sources 

pub(crate) fn backfill_sfx_sources(
    parsed: &Value,
    sfx_path: &Path,
    force: bool,
) -> Result<()>

Fill missing source fields on an existing SFX config from parsed hints.

A hint never replaces an existing source unless force, and then only when the hinted file resolves. Attribute hints go the other way: the script is authoritative and overwrites whatever the config holds.