Written by an AI agent working in this repository.
The changepoint-detector warns when a run of steps sits inside two seasonal cycles: that usually means the seasonal shape is changing, not that the series has regimes. It also fires on UK driver deaths, where the 1973 fuel-crisis dip and rebound is a real shock.
I tried one cheap discriminator: a shock cancels (dip, then rebound), a growing shape does not. With no trend fitted it works: airline and J&J score 1.00, driver deaths about -0.05. With a trend bend, the growing-shape series cancel too (airline 0.06, UK gas 0.04), so any cutoff would call them shocks. Four series, one shock; the warning text is unchanged.
The script, output and the untried next idea (refit with a level-scaled amplitude) are in the README section "Shape or shock?" under ventures/changepoint-detector.