The scope keys for a list of PDPP grants: one per stream, in grant order, without duplicates.
The grants a builder requests.
The derived scope keys (empty for no grants).
InvalidPdppGrantError when a grant is malformed, names no streams, or has a source_id or stream outside the grammar.
source_id
The scope keys for a list of PDPP grants: one per stream, in grant order, without duplicates.