  We present the first JWST observations of the $z=4.11$ luminous radio galaxy
TN J1338-1942, obtained as part of the ``Prime Extragalactic Areas for
Reionization and Lensing Science'' (``PEARLS'') project. Our NIRCam
observations, designed to probe the key rest-frame optical continuum and
emission line features at this redshift, enable resolved spectral energy
distribution modelling that incorporates both a range of stellar population
assumptions and radiative shock models. With an estimated stellar mass of
$\log_{10}(M/\text{M}_{\odot}) \sim 10.9$, TN J1338--1942 is confirmed to be
one of the most massive galaxies known at this epoch. Our observations also
reveal extremely high equivalent-width nebular emission coincident with the
luminous AGN jets that is best fit by radiative shocks surrounded by extensive
recent star-formation. We estimate the total star-formation rate (SFR) could be
as high as $\sim1600\,\text{M}_{\odot}\,\text{yr}^{-1}$, with the SFR that we
attribute to the jet induced burst conservatively
$\gtrsim500\,\text{M}_{\odot}\,\text{yr}^{-1}$. The mass-weighted age of the
star-formation, $t_{\text{mass}} <4$ Myr, is consistent with the likely age of
the jets responsible for the triggered activity and significantly younger than
that measured in the core of the host galaxy. The extreme scale of the
potential jet-triggered star-formation activity indicates the potential
importance of positive AGN feedback in the earliest stages of massive galaxy
formation, with our observations also illustrating the extraordinary prospects
for detailed studies of high-redshift galaxies with JWST.
