When relations-api calls spicedb, it turns out that we always specify a limit for the number of subjects we pull back from spicedb (see code), but this limit is not currently supported in spicedb (see ref):
// optional_concrete_limit is currently unimplemented for LookupSubjects
// and will return an error as of SpiceDB version 1.40.1. This will
// be implemented in a future version of SpiceDB.
uint32 optional_concrete_limit = 7 [
(validate.rules) = {
uint32:

},
(buf.validate.field).uint32.gte = 0
];
 
Therefore LookupSubjects will never work (with spicedb). We need to stop sending this limit, at least as a default, until the feature is added in spicedb.

Error:

 gRPC error: <_MultiThreadedRendezvous of RPC that terminated with:
        status = StatusCode.UNIMPLEMENTED
        details = "error received while streaming subjects from Zanzibar backend: error receiving subject from SpiceDB: rpc error: code = Unimplemented desc = concrete limit is not yet supported"
        debug_error_string = "UNKNOWN:Error received from peer  {created_time:"2025-07-02T11:39:37.077453307+00:00", grpc_status:12, grpc_message:"error received while streaming subjects from Zanzibar backend: error receiving subject from SpiceDB: rpc error: code = Unimplemented desc = concrete limit is not yet supported"}"