The Continue-watching and Surprise rails sorted on `(ts is not None, ts)`. That
key LOOKS null-safe and is not: two rows that both lack a timestamp compare
equal on the flag and then compare `None < None`, which raises — so a show whose
rollup has no `resumed_at`, or a movie state written before
`progress_updated_at` existed, could 500 the rail instead of sorting last.
Replaced with an explicit epoch sentinel, and named it beside the other rail
constants so the sibling rail E24 adds cannot re-derive the same broken key.
peter
5703c4d713