Home Assistant Cloud stopped working after replacing a USG Pro 4 with a UDM Pro Max. The cause was a static IPv6 default route pointing at the old gateway's link-local address.

I wanted to get the depth curves for the lakes in Haldenvassdraget (Halden rivers/lakes) into geojson format.

Depth curves for the lakes of the Halden river system

Using Arrow in Ktor for controlled error handling. Sealed interfaces for error types, Raise for propagation, and extension functions for HTTP responses.