Function list_objects_flat 

pub async fn list_objects_flat(
    client: &Client,
    bucket: &str,
    prefix: &str,
    continuation_token: Option<&str>,
    max_keys: Option<i32>,
) -> Result<ListPage, AppError>

List objects under prefix in bucket without a delimiter.

Returns all keys in the entire prefix tree — no virtual folders. common_prefixes is always empty in the returned ListPage.

Use this for search-over-all or bulk-selection scenarios.