Handling of ISO_STREAM is bogus
connection_edge_compatible_with_circuit prevents a stream with ISO_STREAM set from being associated to any circuit to which a stream (not necessarily a different stream) has already been associated. Nothing else looks at ISO_STREAM. (In other news, connection_edge_streams_are_compatible is dead code.)
This treatment of ISO_STREAM should cause excess circuit creation (legacy/trac#3632 (moved)) during anonymous directory operations, and it does not (explicitly) prevent a circuit which has had an ISO_STREAM stream attached to it from having a non-ISO_STREAM stream attached to it later.