Complete Tour

Mark one onboarding guide as seen. Idempotent.

One endpoint for both finishing and skipping, because the product does not care which happened: the only decision this state drives is "show it again?", and after either the answer is no. Recording them separately would be data nobody is going to act on.

404 on an unknown guide rather than a silent 200. A typo in a guide name would otherwise return success while recording nothing, and the symptom — a tour that reappears on every page load forever — points at the client, not at here.

The timestamp is only written once. A user who replays a guide later has not become newer, and overwriting it would lose the one fact worth keeping: when they first met the product.