imsd: place the re-signed apks with the packages dir's owner

Run 50 got past the key copy and the re-sign, then died on the move into
pmbootstrap's packages dir: abuild created that directory from inside the
chroot, so it belongs to the chroot user (uid 12345) and the build user
cannot write there. Install the files via sudo with the directory's own
owner and mode 0644, as abuild would have left them, and fail with a clear
message if the directory is missing instead of creating a wrongly-owned one.

build.sh

@@ -277,8 +277,20 @@ for _f in "$IMSD_DL"/*.apk; do
 	python3 ./apk-resign.py "$_f" "$KEYCOPY" "$(basename "$ABUILD_KEY").pub"
 done
 rm -f "$KEYCOPY"
-mkdir -p "$WORKDIR/packages/edge/aarch64"
-mv "$IMSD_DL"/*.apk "$WORKDIR/packages/edge/aarch64/"
+# The packages dir belongs to pmbootstrap's chroot user as well (abuild wrote
+# it from inside the chroot), so the build user cannot write there either
+# (run 50): install the files with the directory's own owner, as abuild would
+# have left them. The dir exists because the builds above populated it.
+PKGDIR="$WORKDIR/packages/edge/aarch64"
+if [ ! -d "$PKGDIR" ]; then
+	echo "$PKGDIR missing - the package builds above should have created it" >&2
+	exit 1
+fi
+for _f in "$IMSD_DL"/*.apk; do
+	sudo install -m 0644 -o "$(stat -c %u "$PKGDIR")" -g "$(stat -c %g "$PKGDIR")" \
+		"$_f" "$PKGDIR/$(basename "$_f")"
+done
+rm -f "$IMSD_DL"/*.apk
 pmbootstrap index
 
 # --- 4. build the image -------------------------------------------------------