severity 1066972 important thanks
Indeed, there is no librust-rfc2047-decoder-0.2+default-dev package.
librust-rfc2047-decoder-0.2+default-dev is a virtual package provided by librust-rfc2047-decoder-dev which is built from the rust-rfc2047-decoder source package. Following the dependency chain, it looks like the root cause (or at least one of the root causes) is that the testsuite for rust-stacker is segfaulting on mips64el.