The correct place for debug files is a hash-based path, instead of
the crapfuck we have today.
... but until then, for gdb to pick them up, debug symbols for $THING
must be in /usr/lib/debug/$THING (a general rule, independent of
multiarch),
No, gdb is perfectly able to pick them from /usr/lib/debug/.build-id/.
Since ddeb support in dak is apparently not coming soon, maybe we
should start migrating the existing -dbg packages to this scheme. If it
can help with multiarch as well, this hits two birds with one stone.