Function prune_pretend 

pub async fn prune_pretend(
    pool: &Pool,
    opts: &PruneOptions,
) -> Result<Vec<PruneReport>, ExecError>

--pretend companion to prune_all. Walks the same registry but invokes each entry’s count thunk instead of prune — no rows are deleted. Useful for previewing the impact of a prune against production data before committing.

Errors

Same shape as prune_all — first error short-circuits.