Pre-chamber (PC) ignition is increasingly recognized as an enabling technology for ultra-lean combustion in advanced spark-ignition (SI) engines, particularly for heavy-duty applications where high efficiency and low particulate emissions are critical. The use of a pre-chamber allows enhanced ignition energy and turbulent jet ignition, thereby improving flame initiation and combustion stability under lean operating conditions that are challenging for conventional spark systems. In parallel, methanol is gaining growing interest as an alternative heavy-duty fuel due to its potential for renewable production, favorable combustion chemistry, high knock resistance, and inherently soot-free characteristics, making it well suited for lean-burn engine concepts. This study experimentally examines the lean-burn behavior of a heavy-duty SI engine fueled with methanol in the main chamber and operated with both passive and active PC configurations. The passive PC configuration is used to establish baseline combustion characteristics, highlighting the limitations associated with ignition when the pre-chamber is fueled only through main-chamber charge entrainment. To overcome these limitations, active PC fueling strategies employing hydrogen (H₂), CO/H₂, and CO₂/H₂ mixtures are investigated. These fuels are selected to represent practical pre-chamber energy carriers that can be produced via on-board methanol reforming, offering a pathway to enhanced ignition performance without reliance on dedicated hydrogen storage infrastructure. The influence of different PC fuels on combustion stability, flame development, heat-release behavior, and engine performance is systematically analyzed. Particular emphasis is placed on understanding how fuel properties such as reactivity, mixture density, and jet momentum affect turbulent jet ignition and main-chamber combustion. In addition, the impact of pre-chamber fueling strategies on gaseous emissions is evaluated to assess potential trade-offs between combustion enhancement and emission formation. The outcomes of this work provide insight into the role of reformate-based PC fuels in extending the operability of lean methanol combustion and support the development of practical, high-efficiency, and low-carbon heavy-duty SI engine concepts based on methanol and pre-chamber ignition.