Build Regularly Spaced Panels from Irregularly Spaced Longitudinal Data // Aligns irregularly timed longitudinal observations to regular panel schedules. Each observation on a subject serves as a potential baseline, and all later observations are aligned to the nearest panel with minimal delay. The package provides tools to: (1) build a panel book documenting alignments and delays, (2) organize variables in longitudinal data to wide-format panel matrices, (3) summarize alignment quality and panel coverage. Ideal for cross-lagged panel analysis, clinical trials with variable visit schedules, and Electronic Health Record harmonization.