  Multiple observational lines of evidence support a connection between
hydrogen-poor superluminous supernovae (SLSNe) and long duration gamma-ray
bursts (GRBs). Both events require a powerful central energy source, usually
attributed to a millisecond magnetar or an accreting black hole. The GRB-SLSN
link raises several theoretical questions: What distinguishes the engines
responsible for these different phenomena? Can a single engine power both a GRB
and a luminous SN in the same event? We propose a new unifying model for
magnetar thermalization and jet formation: misalignment between the rotation
(${\bf \Omega}$) and magnetic dipole (${\bf \mu}$) axes thermalizes a fraction
of the spindown power by reconnection in the striped equatorial wind, providing
a guaranteed source of "thermal" emission to power the supernova. The remaining
un-thermalized power energizes a relativistic jet. In this picture, the
GRB-SLSN dichotomy is directly linked to ${\bf \Omega \cdot \mu}$. We extend
earlier work to show that even weak relativistic jets of luminosity
$\sim10^{46}$ erg s$^{-1}$ can escape the expanding SN ejecta hours after the
explosion, implying that escaping relativistic jets may accompany many SLSNe.
We calculate the observational signature of these jets. We show that they may
produce transient UV cocoon emission lasting a few hours when the jet breaks
out of the ejecta surface. A longer-lived optical/UV signal may originate from
a mildly-relativistic wind driven from the interface between the jet and the
ejecta walls. This provides a new explanation for the secondary early-time
maximum observed in some SLSNe light curves, such as LSQ14bdq. This scenario
also predicts a population of GRB from on-axis jets with extremely long
durations, potentially similar to the population of "jetted tidal disruption
events", in coincidence with a small subset of SLSNe.
