  Nearly a decade ago, we began to see indications that reionization-era
galaxies power hard radiation fields rarely seen at lower redshift. Most
striking were detections of nebular CIV emission in what appeared to be typical
low mass galaxies, requiring an ample supply of 48 eV photons to triply ionize
carbon. The nature of this population has long remained unclear owing to
limitations of ground-based spectroscopy. We have obtained deep JWST/NIRSpec
R=1000 spectroscopy of the two z>6 CIV-emitting galaxies known prior to JWST.
Here we present a rest-UV to optical spectrum of one of these two systems, the
multiply-imaged z=6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals two
compact (<22pc) clumps separated by 220pc, with one comprising a dense
concentration of massive stars ($>10,400M_{\odot}$/yr/kpc$^2$) formed in a
recent burst. We stack spectra of 3 images of the galaxy (J=24.8-25.9),
yielding a very deep spectrum providing a high S/N template of strong emission
line sources at z>6. The spectrum reveals narrow high ionization lines (HeII,
CIV, NIV]) with line ratios consistent with powering by massive stars. The
rest-optical spectrum is dominated by very strong emission lines ([OIII]
EW=2800\AA), albeit with weak emission from low-ionization transitions
([OIII]/[OII]=184). The electron density is found to be very
high($6.4-31\times10^4$cm$^{-3}$) based on three UV transitions. The ionized
gas is metal poor ($12+\log(\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highly
enriched in nitrogen ($\log(\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrum
appears broadly similar to that of GNz11 at z=10.6, without showing the same
AGN signatures. We suggest that the hard radiation field and rapid nitrogen
enrichment may be a short-lived phase that many z>6 galaxies go through as they
undergo strong bursts of star formation. We comment on the potential link of
such spectra to globular cluster formation.
