is still an open matter of debate. In certain situations, however, the mechanism responsible for launching the jet operates simultaneously with the release of a large amount of energy in the form of radiation, making it likely that photons dominate the bulk energetics. This scenario occurs, for example, during the super-Eddington phase of jetted tidal disruption events (TDEs), such as *Swift* J1644+57 [@bur11; @zau11] and *Swift* J2058+05 [@cen12]. Radiation-dominated jets should also be present in the collapsar picture of long gamma-ray bursts (GRBs; @ree92 [@woo93; @mes93; @mac99; @pir04]), where the energy released in the form of gamma-rays is ultimately derived from accretion onto a black hole, the associated accretion luminosity exceeding the Eddington limit of the hole by more than ten orders of magnitude. In both of these cases, the propagation of the radiation-dominated jet is modulated by the presence of a radiation pressure-supported environment; for super-Eddington TDEs, this environment is in the form of a highly inflated, quasi-spherical torus of fallback debris [@cou14a], while a “cocoon” of shocked jet material [@mor07; @lop13] and the overlying stellar envelope itself [@mat03; @woo06] serve as the confining medium for GRBs.

In a companion paper (@cou15, hereafter Paper I), we presented a model 