Metal additive manufacturing via laser-based powder bed fusion faces performance-critical challenges due to complex melt pool and vapor dynamics. While computational modeling has advanced significantly, most existing approaches oversimplify laser-induced evaporation by representing it solely as a pressure jump at the melt surface. This simplification neglects essential physical phenomena such as vapor expansion, interfacial velocity discontinuities, and convective heat transfer in the vapor phase. To address these limitations, we present a high-fidelity, multi-phase computational model for melt pool dynamics that resolves melt-vapor interactions at the mesoscale. It captures evaporation-induced mass flux, volume expansion and velocity jumps across the liquid-vapor interface along with convective heat transfer in the gas phase. The model is built upon an anisothermal incompressible Navier--Stokes solver coupled with a conservative diffuse-interface scheme using a level-set formulation. A high-performance solution strategy is employed via a matrix-free, adaptive finite element framework based on the open-source library deal.II. A key concept lies in our consistent formulations of interface source terms and level-set transport velocities. These are obtained via projections from the sharp liquid--vapor interface onto the computational grid along the interface thickness direction. This approach significantly improves the accuracy of the diffuse-interface framework despite extreme interfacial density, pressure and velocity gradients. Additionally, we incorporate a hybrid recoil pressure model -- extending Anisimov’s formulation for consistency with gas dynamics -- to capture realistic melt pool fluctuations with a vapor jet. Simulations of stationary laser illumination on a bare metal plate demonstrate that the presented model captures the strong coupling between melt and vapor flow dynamics, despite the numerically favorable assumption of incompressible vapor. Most notably, we show that projection-based level-set transport velocity formulations are critical for enabling accurate predictions of the evaporated mass and the melt-vapor dynamics within a diffuse-interface framework.