Massive stars rarely form in isolation. Their birth is embedded in a multiscale habitat connecting Galactic filamentary clouds, parsec-scale clumps and fragments, intercore gas, and thousand-au star-forming cores. Understanding how matter is redistributed across this hierarchy, and how the habitat changes with evolution, is central to explaining massive cluster formation. The 14-parsec-long G316.8 filament provides a controlled laboratory. Its three contiguous subregions contain comparable molecular-gas reservoirs of approximately 10,000 solar masses, yet span an evolutionary sequence from an infrared-dark cloud, through a massive protostellar region, to an H II region hosting a young massive cluster. The Linear Filament and Nested Cluster Evolution Tomography project, LANCET, combines ALMA 12-meter and ACA 7-meter observations with reconstructed total-power emission to recover the 1.3-millimeter continuum from the filament scale down to dense cores. Our all-scale analysis identifies 231 dense cores and reveals progressive mass concentration. From the young to the evolved region, the fraction of cloud mass assembled into sub-parsec fragments increases by more than a factor of twenty, while the fraction contained in cores rises by approximately a factor of eight. The strongest cross-scale relation links the intercore surface density immediately surrounding each core to its parsec-scale environment, with a correlation coefficient of approximately 0.72. Preliminary C18O results further reveal multiple velocity components in the infrared-dark region and shell- or ripple-like structures near the H II region. Together, these results portray massive star formation as the evolution of an interconnected habitat rather than the isolated collapse of individual cores.
