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Nearly a decade ago, we began to see indications that reionization-eragalaxies power hard radiation fields rarely seen at lower redshift. Moststriking were detections of nebular CIV emission in what appeared to be typicallow mass galaxies, requiring an ample supply of 48 eV photons to triply ionizecarbon. The nature of this population has long remained unclear owing tolimitations of ground-based spectroscopy. We have obtained deep JWST/NIRSpecR=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, themultiply-imaged z=6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals twocompact (<22pc) clumps separated by 220pc, with one comprising a denseconcentration of massive stars ($>10,400M_{\odot}$/yr/kpc$^2$) formed in arecent 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 emissionline sources at z>6. The spectrum reveals narrow high ionization lines (HeII,CIV, NIV]) with line ratios consistent with powering by massive stars. Therest-optical spectrum is dominated by very strong emission lines ([OIII]EW=2798\AA), albeit with weak emission from low-ionization transitions([OIII]/[OII]=184). The electron density is found to be veryhigh($6.4-31\times10^4$cm$^{-3}$) based on three UV transitions. The ionizedgas is metal poor ($12+\log(\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highlyenriched in nitrogen ($\log(\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrumappears broadly similar to that of GNz11 at z=10.6, without showing the sameAGN signatures. We suggest that the hard radiation field and rapid nitrogenenrichment may be a short-lived phase that many z>6 galaxies go through as theyundergo strong bursts of star formation. We comment on the potential link ofsuch spectra to globular cluster formation.

Metal-poor star formation at $z>6$ with JWST: new insight into hard radiation fields and nitrogen enrichment on 20 pc scales