This isn't necessary. Because we just log the error, we never match off of it,
we don't need any structure beyond String (or now Debug, which still gives us
a way to print the error). This is for the ergonomics of not having to
constantly write `.map_err(|e| format!("{e:?}"))`.
It's only there to make the VariantSignid unique across Sessions. By localizing
the VariantSignid to a Session, we avoid this, and can better ensure we don't
queue work for historic sessions.
