Complex natural-product pathways are increasingly reconstructed outside their native organisms, yet successful biosynthesis is often interpreted too broadly as evidence of pathway portability or manufacturing readiness. Cell-free and cell-based systems solve different parts of this problem and expose different constraints. We conducted a qualitative evidence-mapping review of peer-reviewed Q1-journal literature published from 2017 through 2026. Searches covered cell-free biosynthesis, heterologous cellular production, pathway reconstruction, enzyme compatibility, energy/cofactor and precursor demand, compartmentation, burden, process control, and readiness. Fifty-five DOI-normalized candidates were screened; 49 full texts were assessed and 39 studies were mapped. Evidence was coded by platform, pathway class, enzyme constraint, resource demand, context, process evidence, portability level, and transferability boundary. Cell-free evidence shows high experimental access to enzyme behavior, energy balance, pathway modularity, extract provenance, maturation requirements, and temporal control. Cell-based evidence demonstrates reconstruction of increasingly complex plant and microbial pathways while revealing constraints from precursor supply, heterologous enzyme function, toxicity, spatial organization, transport, and host fitness. Across both platforms, pathway completion is not equivalent to process robustness or scale readiness. The evidence instead supports a proposed staged interpretation in which pathway knowledge, biochemical function, pathway-level production, and process evidence are assessed separately. Cell-free and cell-based biosynthesis are best interpreted as conditionally complementary rather than universally substitutable production strategies. Comparative inference remains limited by heterogeneous products, reaction formats, hosts, and scarce shared readiness benchmarks.
