Function parse_read_scopes 

pub fn parse_read_scopes(s: &str) -> Result<ReadScopes, String>

Parses a comma-separated list of shared (case-insensitive) or scope ULIDs. Whitespace around each entry is ignored. Order and duplicates are preserved. Rejects an empty list ("", " , "). Each token is parsed via resolve_scope — the default passed there is never used because every token is required.