  We present the JWST discovery of SN 2023adsy, a transient object located in a
host galaxy JADES-GS$+53.13485$$-$$27.82088$ with a host spectroscopic redshift
of $2.903\pm0.007$. The transient was identified in deep James Webb Space
Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic
Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and
NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR
color, and spectroscopic information all consistent with a Type Ia
classification. Despite its classification as a likely SN Ia, SN 2023adsy is
both fairly red (E(B-V)$\sim0.9$) despite a host galaxy with low-extinction and
has a high Ca II velocity ($19,000\pm2,000$km/s) compared to the general
population of SNe Ia. While these characteristics are consistent with some
Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter
than the low-z Ca-rich population. Although such an object is too red for any
low-z cosmological sample, we apply a fiducial standardization approach to SN
2023adsy and find that the SN 2023adsy luminosity distance measurement is in
excellent agreement ($\lesssim1\sigma$) with $\Lambda$CDM. Therefore unlike
low-z Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication
that SN Ia standardized luminosities change significantly with redshift. A
larger sample of distant SNe Ia is required to determine if SN Ia population
characteristics at high-z truly diverge from their low-z counterparts, and to
confirm that standardized luminosities nevertheless remain constant with
redshift.
