Function objects_list_flat 

pub async fn objects_list_flat(
    profile_id: ProfileId,
    bucket: BucketId,
    prefix: String,
    continuation_token: Option<String>,
    force: Option<bool>,
    store: State<'_, ProfileStoreHandle>,
    pool: State<'_, S3ClientPoolHandle>,
    cache: State<'_, CacheHandle>,
    _channel: AppHandle,
) -> Result<ListPage, AppError>

List all objects under prefix without a delimiter (flat key tree).

Uses the same validation gate and first-page caching as objects_list, but with a distinct cache-key suffix ("__FLAT__") to avoid collision.