Path-Integrated Difference-in-Differences // Implements the Path- Integrated Difference-in-Differences ('PI-DiD') framework of Salavi (2026), which treats the treatment effect as a trajectory tau(t) = c1(t) - c0(t) and integrates the baseline- differenced gap over a post-treatment window to obtain a cumulative causal effect and a path-integrated average treatment effect on the treated, together with cluster-robust standard errors, confidence intervals, diagnostic plots, and the pre-treatment parallel-trends, grid-density, and anticipation-robustness checks of section 5 of the companion paper. This approach avoids the endpoint-subtraction bias that arises whenever a transitory policy's effect has fully decayed by the evaluation date, in which case the conventional static difference-in-differences estimate can be zero even though the cumulative benefit delivered to treated units was strictly positive. Formerly distributed as a Stata package under the names 'pidid' and 'pididplot'.