The JDISC Survey: Inner Disk Chemistry of Class I/FS Disks and Tentative Evidence for Early Pebble Drift

We present the first chemical survey of Class I and Flat-Spectrum (I/FS) disks using JWST MIRI/MRS, targeting sixteen sources in the Ophiuchus star-forming region. Through empirical line luminosity measurements and multi-component slab modeling, we characterize the molecular reservoir of these young systems and compare them to twelve Class II disks of similar stellar mass. Water, HCN, C 2 H 2, and CO 2 are frequently detected in I/FS sources with inclinations i < 70, whereas edge-on systems show significantly suppressed emission. Compared to Class II disks, I/FS sources show suggestive---though not yet statistically significant---evidence for elevated cold water (about 200,K) mass and lower CO 2 excitation temperatures. Statistical analyses identify accretion luminosity as the primary correlate of molecular mass across both evolutionary stages. Once this dependence is removed, cold water and CO 2 masses anti-correlate with mm-dust disk radius, while hot water remains insensitive to disk size. These patterns are qualitatively consistent with pebble drift models that predict early water enrichment followed by delayed CO 2 delivery, suggesting an evolutionary progression from molecular-poor Class 0 sources, through water-rich Class I/FS disks, to Class II disks with reduced cold water excess. This work provides an initial evolutionary framework for disk chemistry that requires larger, multi-region samples to confirm.