  We show that several models of interacting XXZ spin chains subject to
boundary driving and dissipation possess a subtle kind of time-reversal
symmetry, making their steady states exactly solvable. We focus on a model with
a coherent boundary drive, showing that it exhibits a unique continuous
dissipative phase transition as a function of the boundary drive amplitude.
This transition has no analogue in the bulk closed system, or in incoherently
driven models. We also show the steady state magnetization exhibits a
surprising fractal dependence on interaction strength, something previously
associated with less easily measured infinite-temperature transport quantities
(the Drude weight). Our exact solution also directly yields driven-dissipative
double-chain models that have pure, entangled steady states that are also
current carrying.
