otel/format-traceparent + otel/current-traceparent emit '00-<32hex>-<16hex>-01';
otel/parse-traceparent round-trips it (nil on malformed/bad-width). otel/-timed
now guards the thunk: success spans get :status ok, a raised error records a
span with :status error + an exception event then propagates. Error propagation
uses a false-returning guard clause test (an explicit (raise e) in a guard
handler re-enters the guard and hangs).