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AF Lep A+b is a remarkable planetary system hosting a gas-giant planet thathas the lowest dynamical mass among directly imaged exoplanets. We present anin-depth analysis of the atmospheric composition of the star and planet toprobe the planet's formation pathway. Based on new high-resolution spectroscopyof AF Lep A, we measure a uniform set of stellar parameters and elementalabundances (e.g., [Fe/H] = $-0.27 \pm 0.31$ dex). The planet's dynamical mass($2.8^{+0.6}_{-0.5}$ M$_{\rm Jup}$) and orbit are also refined using publishedradial velocities, relative astrometry, and absolute astrometry. We usepetitRADTRANS to perform chemically-consistent atmospheric retrievals for AFLep b. The radiative-convective equilibrium temperature profiles areincorporated as parameterized priors on the planet's thermal structure, leadingto a robust characterization for cloudy self-luminous atmospheres. This novelapproach is enabled by constraining the temperature-pressure profiles via thetemperature gradient $(d\ln{T}/d\ln{P})$, a departure from previous studiesthat solely modeled the temperature. Through multiple retrievals performed ondifferent portions of the $0.9-4.2$ $\mu$m spectrophotometry, along withdifferent priors on the planet's mass and radius, we infer that AF Lep b likelypossesses a metal-enriched atmosphere ([Fe/H] $> 1.0$ dex). AF Lep b'spotential metal enrichment may be due to planetesimal accretion, giant impacts,and/or core erosion. The first process coincides with the debris disk in thesystem, which could be dynamically excited by AF Lep b and lead to planetesimalbombardment. Our analysis also determines $T_{\rm eff} \approx 800$ K,$\log{(g)} \approx 3.7$ dex, and the presence of silicate clouds anddis-equilibrium chemistry in the atmosphere. Straddling the L/T transition, AFLep b is thus far the coldest exoplanet with suggested evidence of silicateclouds.

ELemental abundances of Planets and brown dwarfs Imaged around Stars  (ELPIS): I. Potential Metal Enrichment of the Exoplanet AF Lep b and a Novel  Retrieval Approach for Cloudy Self-luminous Atmospheres