Don't Let Sleeping Stars Li: Mapping Turnoff Lithium, the Lithium Dip & Testing Standard Model Predictions in GALAH DR4

Lithium is a tracer of stellar mixing, with a complex nucleosynthetic origin. We present a reconstruction of the end of the MS Li depletion pattern across a range of masses and metallicities. We do so using the GALAH DR4 3D-NLTE lithium dataset and published catalogs to screen out photometric binaries. We complement this data with masses and subgiant Li dilution factors inferred from YREC stellar models. We find good agreement between predicted and observed Li dilution trends in cool subgiants, and some evidence for anomalies tied to microscopic diffusion in hotter stars. We recover the 3 main features of the main sequence pattern seen in clusters - a cool plateau ($\mathrm{M} \sim 1.2 \mathrm{M_\odot}$), with a median abundance of $\ali = 2.42$), a steep drop into a Li dip ($\mathrm{M} \sim 1.35 \mathrm{M_\odot}$) dominated by upper limits at $\ali=1.5$, and a higher mass population that spans a wide range of Li abundances. The cool plateau is 0.8 dex below solar meteoritic across a wide range of metallicities, with a significant intrinsic dispersion. The higher-mass subgiants have a wide range of abundances, with the upper envelope below the open cluster analog values. At high and low metallicity, we argue that the hot stars sample arises primarily from blue straggler stars, with a much lower detection fraction than that of solar metallicity stars. We detect Li in 20-30\% of Li dip stars, unlike the cluster patterns. We argue that binary contamination cannot fully explain this population. Lithium depletion with intrinsic dispersion is a universal feature of the sample. Our results highlight the importance of non-standard physical mechanisms such as rotationally-induced mixing, gravitational settling, and radiative acceleration.