fix: make dev-vm.sh work on Linux with fallback ISO extraction methods

- Try bsdtar first (macOS + Linux with libarchive-tools)
- Fall back to isoinfo (genisoimage/cdrtools)
- Fall back to loop mount (Linux only, requires root)
- Platform-aware error messages for e2fsprogs install

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

hack/dev-vm.sh

@@ -66,7 +66,12 @@ if [ -n "$MKFS_EXT4" ]; then
     echo "    Data disk: 2 GB ext4 (persistent)"
 else
     echo "ERROR: mkfs.ext4 not found. Install e2fsprogs:"
-    echo "  brew install e2fsprogs"
+    if [ "$(uname)" = "Darwin" ]; then
+        echo "  brew install e2fsprogs"
+    else
+        echo "  apt install e2fsprogs   # Debian/Ubuntu"
+        echo "  dnf install e2fsprogs   # Fedora/RHEL"
+    fi
     exit 1
 fi
 
@@ -109,27 +114,65 @@ case "$IMAGE" in
             INITRAMFS="$ROOTFS_DIR/kubesolo-os.gz"
             echo "    Using kernel/initramfs from build directory"
         else
-            # Extract from ISO using bsdtar (works on macOS + Linux, no mount needed)
+            # Extract kernel + initramfs from ISO.
+            # Try multiple methods: bsdtar > isoinfo > loop mount
             EXTRACT_DIR="$(mktemp -d /tmp/kubesolo-extract-XXXXXX)"
+            EXTRACTED=0
 
             echo "    Extracting kernel/initramfs from ISO..."
-            bsdtar -xf "$IMAGE" -C "$EXTRACT_DIR" boot/vmlinuz boot/kubesolo-os.gz 2>/dev/null || {
+
+            # Method 1: bsdtar (ships with macOS, libarchive-tools on Linux)
+            if [ $EXTRACTED -eq 0 ] && command -v bsdtar >/dev/null 2>&1; then
+                if bsdtar -xf "$IMAGE" -C "$EXTRACT_DIR" boot/vmlinuz boot/kubesolo-os.gz 2>/dev/null; then
+                    echo "    Extracted via bsdtar"
+                    EXTRACTED=1
+                fi
+            fi
+
+            # Method 2: isoinfo (genisoimage/cdrtools on Linux)
+            if [ $EXTRACTED -eq 0 ] && command -v isoinfo >/dev/null 2>&1; then
+                mkdir -p "$EXTRACT_DIR/boot"
+                isoinfo -i "$IMAGE" -x "/BOOT/VMLINUZ;1" > "$EXTRACT_DIR/boot/vmlinuz" 2>/dev/null || true
+                isoinfo -i "$IMAGE" -x "/BOOT/KUBESOLO-OS.GZ;1" > "$EXTRACT_DIR/boot/kubesolo-os.gz" 2>/dev/null || true
+                # isoinfo writes empty files on failure; check size
+                if [ -s "$EXTRACT_DIR/boot/vmlinuz" ] && [ -s "$EXTRACT_DIR/boot/kubesolo-os.gz" ]; then
+                    echo "    Extracted via isoinfo"
+                    EXTRACTED=1
+                else
+                    rm -f "$EXTRACT_DIR/boot/vmlinuz" "$EXTRACT_DIR/boot/kubesolo-os.gz"
+                fi
+            fi
+
+            # Method 3: loop mount (Linux only, requires root)
+            if [ $EXTRACTED -eq 0 ] && [ "$(uname)" = "Linux" ]; then
+                ISO_MOUNT="$EXTRACT_DIR/mnt"
+                mkdir -p "$ISO_MOUNT"
+                if mount -o loop,ro "$IMAGE" "$ISO_MOUNT" 2>/dev/null; then
+                    mkdir -p "$EXTRACT_DIR/boot"
+                    cp "$ISO_MOUNT/boot/vmlinuz" "$EXTRACT_DIR/boot/" 2>/dev/null || true
+                    cp "$ISO_MOUNT/boot/kubesolo-os.gz" "$EXTRACT_DIR/boot/" 2>/dev/null || true
+                    umount "$ISO_MOUNT" 2>/dev/null || true
+                    if [ -f "$EXTRACT_DIR/boot/vmlinuz" ] && [ -f "$EXTRACT_DIR/boot/kubesolo-os.gz" ]; then
+                        echo "    Extracted via loop mount"
+                        EXTRACTED=1
+                    fi
+                fi
+            fi
+
+            if [ $EXTRACTED -eq 0 ]; then
                 echo "ERROR: Failed to extract kernel/initramfs from ISO."
-                echo "  Ensure bsdtar is available (ships with macOS, install libarchive on Linux)."
+                echo "  Install one of: bsdtar (libarchive-tools), isoinfo (genisoimage), or run as root for loop mount."
                 echo "  Or run 'make rootfs initramfs' to produce build artifacts."
                 exit 1
-            }
+            fi
 
             VMLINUZ="$EXTRACT_DIR/boot/vmlinuz"
             INITRAMFS="$EXTRACT_DIR/boot/kubesolo-os.gz"
 
             if [ ! -f "$VMLINUZ" ] || [ ! -f "$INITRAMFS" ]; then
                 echo "ERROR: ISO does not contain expected boot/vmlinuz and boot/kubesolo-os.gz"
-                echo "  ISO contents:"
-                bsdtar -tf "$IMAGE" 2>/dev/null || true
                 exit 1
             fi
-            echo "    Extracted kernel/initramfs from ISO"
         fi
 
         qemu-system-x86_64 \