Both packagers copied the staged UAPI headers with:
cp -a /out/staging/headers/usr "$DEST/usr"
Because $DEST/usr already exists (modules live under $STAGING/usr/lib/modules,
and other files may be staged under $PKG/usr), cp placed the source directory
inside the destination, producing a nested usr/usr/include/ path. The headers
were therefore installed at the wrong location and not found by builds.
Merge the contents with cp -a .../usr/. "$DEST/usr/" so the headers land at
the expected /usr/include/linux/... path in both .deb and .pkg.tar.zst
packages.
