Independent Archival Reconstruction and Multibeam Assessment of FAST Narrowband Candidate NBS 260108

Selected native-channel FAST spectra from project PT2021_0145 were re-examined to reconstruct the narrowband feature reported by Li et al. (2026) toward K2-155 near 1148.4167 MHz. The analysis covers 13 real primary-beam integrations in eight temporal blocks, an 18-beam comparison, and sparse cross-target controls. Along a literature-informed, subsequently frozen −0.038 Hz/s frequency trajectory, provisional spectral product P1 remains locally enhanced across all eight sampled temporal blocks. A six-integration stack yields a WaveSETI-style median/MAD-normalized score of +5.432 at the candidate channel. This is not equivalent to the published full-observation detection signal-to-noise ratio. The multibeam analysis shows primary-beam dominance with a weaker, nonpersistent off-beam coincidence. A separate exploratory spectral feature displays variable behaviour across different telescope pointings. The investigation provides a documented and reproducible partial archival reconstruction of reported spectral behaviour. It does not establish an astrophysical or extraterrestrial origin for the signal. The accompanying documentary archive contains 65 files, including analysis scripts, numerical results and verified provenance records. Original FAST FITS observations and complete instrumental calibration data are not included. Status: Preliminary, non-peer-reviewed technical reanalysis.