fix: complete ARM64 RPi build pipeline

- fetch-components.sh: download ARM64 KubeSolo binary (kubesolo-arm64)
- inject-kubesolo.sh: use arch-specific binaries for KubeSolo, cloud-init,
  and update agent; detect KVER from custom kernel when rootfs has none;
  cross-arch module resolution via find fallback when modprobe fails
- create-rpi-image.sh: kpartx support for Docker container builds
- Makefile: rootfs-arm64 depends on build-cross, includes pack-initramfs

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

build/scripts/inject-kubesolo.sh

@@ -25,7 +25,11 @@ if [ ! -d "$ROOTFS" ]; then
     exit 1
 fi
 
-KUBESOLO_BIN="$CACHE_DIR/kubesolo"
+if [ "$INJECT_ARCH" = "arm64" ]; then
+    KUBESOLO_BIN="$CACHE_DIR/kubesolo-arm64"
+else
+    KUBESOLO_BIN="$CACHE_DIR/kubesolo"
+fi
 if [ ! -f "$KUBESOLO_BIN" ]; then
     echo "ERROR: KubeSolo binary not found: $KUBESOLO_BIN"
     echo "See fetch-components.sh output for instructions."
@@ -78,23 +82,27 @@ for lib in network.sh health.sh; do
 done
 
 # Cloud-init binary (Go, built separately)
-CLOUDINIT_BIN="$CACHE_DIR/kubesolo-cloudinit"
+# Try arch-specific binary first, then fall back to generic
+CLOUDINIT_BIN="$CACHE_DIR/kubesolo-cloudinit-linux-$INJECT_ARCH"
+[ ! -f "$CLOUDINIT_BIN" ] && CLOUDINIT_BIN="$CACHE_DIR/kubesolo-cloudinit"
 if [ -f "$CLOUDINIT_BIN" ]; then
     cp "$CLOUDINIT_BIN" "$ROOTFS/usr/lib/kubesolo-os/kubesolo-cloudinit"
     chmod +x "$ROOTFS/usr/lib/kubesolo-os/kubesolo-cloudinit"
     echo "    Installed cloud-init binary ($(du -h "$CLOUDINIT_BIN" | cut -f1))"
 else
-    echo "    WARN: Cloud-init binary not found (run 'make build-cloudinit' to build)"
+    echo "    WARN: Cloud-init binary not found (run 'make build-cloudinit' or 'make build-cross' to build)"
 fi
 
 # Update agent binary (Go, built separately)
-UPDATE_BIN="$CACHE_DIR/kubesolo-update"
+# Try arch-specific binary first, then fall back to generic
+UPDATE_BIN="$CACHE_DIR/kubesolo-update-linux-$INJECT_ARCH"
+[ ! -f "$UPDATE_BIN" ] && UPDATE_BIN="$CACHE_DIR/kubesolo-update"
 if [ -f "$UPDATE_BIN" ]; then
     cp "$UPDATE_BIN" "$ROOTFS/usr/lib/kubesolo-os/kubesolo-update"
     chmod +x "$ROOTFS/usr/lib/kubesolo-os/kubesolo-update"
     echo "    Installed update agent ($(du -h "$UPDATE_BIN" | cut -f1))"
 else
-    echo "    WARN: Update agent not found (run 'make build-update-agent' to build)"
+    echo "    WARN: Update agent not found (run 'make build-update-agent' or 'make build-cross' to build)"
 fi
 
 # --- 3. Custom kernel or TCZ kernel modules ---
@@ -115,8 +123,16 @@ for d in "$ROOTFS"/lib/modules/*/; do
     [ -d "$d" ] && KVER="$(basename "$d")" && break
 done
 
+# Fallback: detect from custom kernel modules directory
+if [ -z "$KVER" ] && [ -d "$CUSTOM_MODULES/lib/modules" ]; then
+    for d in "$CUSTOM_MODULES"/lib/modules/*/; do
+        [ -d "$d" ] && KVER="$(basename "$d")" && break
+    done
+    echo "    Detected kernel version from custom kernel: $KVER"
+fi
+
 if [ -z "$KVER" ]; then
-    echo "    WARN: Could not detect kernel version from rootfs"
+    echo "    WARN: Could not detect kernel version from rootfs or custom kernel"
 fi
 
 echo "    Kernel version: $KVER"
@@ -145,24 +161,49 @@ if [ -f "$CUSTOM_VMLINUZ" ] && [ -d "$CUSTOM_MODULES/lib/modules/$KVER" ]; then
         [ -f "$CUSTOM_MOD_DIR/$f" ] && cp "$CUSTOM_MOD_DIR/$f" "$ROOTFS/lib/modules/$KVER/"
     done
 
-    # Use modprobe --show-depends to resolve each module + its transitive deps
+    # Resolve and install modules from modules.list + transitive deps
     if [ "$INJECT_ARCH" = "arm64" ]; then
         MODULES_LIST="$PROJECT_ROOT/build/config/modules-arm64.list"
     else
         MODULES_LIST="$PROJECT_ROOT/build/config/modules.list"
     fi
     NEEDED_MODS=$(mktemp)
+
+    # Try modprobe first (works for same-arch builds)
+    MODPROBE_WORKS=true
+    FIRST_MOD=$(grep -v '^#' "$MODULES_LIST" | grep -v '^$' | head -1 | xargs)
+    if ! modprobe -S "$KVER" -d "$CUSTOM_MODULES" --show-depends "$FIRST_MOD" >/dev/null 2>&1; then
+        MODPROBE_WORKS=false
+        echo "    modprobe cannot resolve modules (cross-arch build) — using find fallback"
+    fi
+
     while IFS= read -r mod; do
         # Skip comments and blank lines
         case "$mod" in \#*|"") continue ;; esac
         mod=$(echo "$mod" | xargs)  # trim whitespace
         [ -z "$mod" ] && continue
 
-        # modprobe -S <ver> -d <root> --show-depends <module> lists all deps in load order
-        # Output format: "insmod /path/to/module.ko" — extract path with awk
-        modprobe -S "$KVER" -d "$CUSTOM_MODULES" --show-depends "$mod" 2>/dev/null \
-            | awk '/^insmod/{print $2}' >> "$NEEDED_MODS" \
-            || echo "    WARN: modprobe could not resolve: $mod"
+        if [ "$MODPROBE_WORKS" = true ]; then
+            # modprobe -S <ver> -d <root> --show-depends <module> lists all deps in load order
+            modprobe -S "$KVER" -d "$CUSTOM_MODULES" --show-depends "$mod" 2>/dev/null \
+                | awk '/^insmod/{print $2}' >> "$NEEDED_MODS" \
+                || echo "    WARN: modprobe could not resolve: $mod"
+        else
+            # Cross-arch fallback: find module by name in kernel tree
+            found=$(find "$CUSTOM_MOD_DIR/kernel" -name "${mod}.ko" -o -name "${mod}.ko.xz" -o -name "${mod}.ko.gz" -o -name "${mod}.ko.zst" 2>/dev/null | head -1)
+            if [ -n "$found" ]; then
+                echo "$found" >> "$NEEDED_MODS"
+            else
+                # Try replacing hyphens with underscores and vice versa
+                mod_alt=$(echo "$mod" | tr '-' '_')
+                found=$(find "$CUSTOM_MOD_DIR/kernel" -name "${mod_alt}.ko" -o -name "${mod_alt}.ko.xz" -o -name "${mod_alt}.ko.gz" -o -name "${mod_alt}.ko.zst" 2>/dev/null | head -1)
+                if [ -n "$found" ]; then
+                    echo "$found" >> "$NEEDED_MODS"
+                else
+                    echo "    WARN: could not find module: $mod"
+                fi
+            fi
+        fi
     done < "$MODULES_LIST"
 
     # Deduplicate and copy each needed module