`circuit_t::timestamp_dirty` is used in multiple bizarre ways, which should be reverse-engineered, documented, and cleaned up (probably by replacing it with multiple fields, each with a name which reflects its actual meaning and/or purpose). See also the legacy/trac#7157 review discussion. Also, is there a good reason for it to be in `circuit_t`, not `origin_circuit_t`? (Any use of it on `or_circuit_t`s (or even on service-side rendezvous `origin_circuit_t`s) would have different semantics.)