feat: replace Alpine mkinitfs with minimal ALARM-compatible initrd

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/mkinitrd.sh

@@ -1,7 +1,51 @@
 #!/bin/bash
+# Create a minimal initramfs for the stock H700 kernel.
+# The stock kernel has most drivers built-in, so we just need
+# a minimal init that mounts rootfs and exec's /sbin/init.
+set -e
 
-podman run --arch=arm64 --security-opt=label=disable \
-	-v "${2:-./artifacts}:/artifacts" \
-	-v ./mkinitfs.conf:/tmp/mkinitfs.conf:ro \
-	--rm "docker.io/library/alpine:${1:-latest}" \
-	sh -c "apk update && apk add mkinitfs apk-tools && mkinitfs -c /tmp/mkinitfs.conf -n -o /artifacts/initramfs"
+outdir="${1:-./artifacts}"
+tmp="$(mktemp -d)"
+trap 'rm -rf "$tmp"' 0
+
+mkdir -p "$tmp"/{bin,dev,proc,sys,newroot}
+
+# Use busybox from host or build a static one
+# For now, create a minimal shell init script
+cat > "$tmp/init" << 'INITEOF'
+#!/bin/busybox sh
+/bin/busybox mount -t proc none /proc
+/bin/busybox mount -t sysfs none /sys
+/bin/busybox mount -t devtmpfs none /dev
+
+# Find the root partition (partition 5 = rootfs)
+root=""
+for dev in /dev/mmcblk0p5 /dev/mmcblk0p4; do
+    if [ -b "$dev" ]; then
+        root="$dev"
+        break
+    fi
+done
+
+if [ -z "$root" ]; then
+    echo "Cannot find root partition!"
+    /bin/busybox sh
+fi
+
+/bin/busybox mount -t ext4 "$root" /newroot
+exec /bin/busybox switch_root /newroot /sbin/init
+INITEOF
+chmod +x "$tmp/init"
+
+# Get a static busybox for aarch64
+if [ ! -f "$outdir/busybox" ]; then
+    podman run --arch=aarch64 --security-opt=label=disable \
+        -v "$(realpath "$outdir"):/out" \
+        --rm "docker.io/library/alpine:latest" \
+        sh -c "apk add busybox-static && cp /bin/busybox.static /out/busybox"
+fi
+cp "$outdir/busybox" "$tmp/bin/busybox"
+chmod +x "$tmp/bin/busybox"
+
+# Create initramfs
+(cd "$tmp" && find . | cpio -o -H newc 2>/dev/null | gzip > "$outdir/initramfs")