build.sh: create static loop + dm device nodes in the container

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

build.sh

@@ -36,6 +36,17 @@ if [ "$(id -u)" = 0 ]; then
 	mkdir -p /usr/local/sbin
 	printf '#!/bin/sh\nexit 0\n' > /usr/local/sbin/modprobe
 	chmod +x /usr/local/sbin/modprobe
+	# A privileged container's /dev is a snapshot from container start —
+	# loop/dm nodes the host creates later never appear. Create the static
+	# nodes here; opening them autoloads the drivers host-side (reserved
+	# major/minors: loop = block 7,N; device-mapper control = char 10,236).
+	i=0
+	while [ $i -le 15 ]; do
+		[ -b /dev/loop$i ] || mknod -m 660 /dev/loop$i b 7 $i
+		i=$((i + 1))
+	done
+	mkdir -p /dev/mapper
+	[ -c /dev/mapper/control ] || mknod -m 600 /dev/mapper/control c 10 236
 	id build >/dev/null 2>&1 || adduser -D build
 	echo 'build ALL=(ALL) NOPASSWD: ALL' > /etc/sudoers.d/build
 	rm -rf dist