Function require_share_reader 

pub async fn require_share_reader(
    app: &App,
    tn_id: TnId,
    file_id: &str,
    auth: &AuthCtx,
    tenant_id_tag: &str,
) -> ClResult<ShareAuthority>

Authorize listing a file’s share entries or share links.

Weaker than require_share_manager: any Write-access caller — including a plain FSHR-W grantee — may see who the file is shared with, since enumeration is not part of the re-share escalation that gate defends against. Scoped tokens are still rejected. Managers always pass, even at AccessLevel::Read — a creator who may mint and revoke links must be able to list them.