I want to copy a graph from one repo to another.

The SPARQL Graph Protocol has respective operations (GET, PUT, POST)
(though I need to sequence them manually: GET and save as file; POST using that file's content).

But I think it's a valid use case to be able do that in SPARQL.
There are data workflows with electrical CIM that involve materialization of Difference models and reasoning, where COPY (maybe even other Update operations) across repos would be very useful.

No known workaround, since federation (SERVICE) doesn't support named graphs.