diff --git a/cloud/agent/install.go b/cloud/agent/install.go
index cdc8fa5..914b0be 100644
--- a/cloud/agent/install.go
+++ b/cloud/agent/install.go
@@ -9,7 +9,6 @@
 	_ "embed"
 	"errors"
 	"fmt"
-	"io/fs"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -23,24 +22,28 @@
 	"source.monogon.dev/osbase/build/mkimage/osimage"
 	"source.monogon.dev/osbase/efivarfs"
 	npb "source.monogon.dev/osbase/net/proto"
+	"source.monogon.dev/osbase/structfs"
 )
 
 //go:embed metropolis/node/core/abloader/abloader.efi
 var abloader []byte
 
-// FileSizedReader is a small adapter from fs.File to fs.SizedReader
-// Panics on Stat() failure, so should only be used with sources where Stat()
-// cannot fail.
-type FileSizedReader struct {
-	fs.File
+// zipBlob looks up a file in a [zip.Reader] and adapts it to [structfs.Blob].
+func zipBlob(reader *zip.Reader, name string) (zipFileBlob, error) {
+	for _, file := range reader.File {
+		if file.Name == name {
+			return zipFileBlob{file}, nil
+		}
+	}
+	return zipFileBlob{}, fmt.Errorf("file %q not found", name)
 }
 
-func (f FileSizedReader) Size() int64 {
-	stat, err := f.Stat()
-	if err != nil {
-		panic(err)
-	}
-	return stat.Size()
+type zipFileBlob struct {
+	*zip.File
+}
+
+func (f zipFileBlob) Size() int64 {
+	return int64(f.File.UncompressedSize64)
 }
 
 // install dispatches OSInstallationRequests to the appropriate installer
@@ -115,16 +118,14 @@
 	if err != nil {
 		return fmt.Errorf("failed to open node bundle: %w", err)
 	}
-	efiPayload, err := bundle.Open("kernel_efi.efi")
+	efiPayload, err := zipBlob(bundle, "kernel_efi.efi")
 	if err != nil {
 		return fmt.Errorf("invalid bundle: %w", err)
 	}
-	defer efiPayload.Close()
-	systemImage, err := bundle.Open("verity_rootfs.img")
+	systemImage, err := zipBlob(bundle, "verity_rootfs.img")
 	if err != nil {
 		return fmt.Errorf("invalid bundle: %w", err)
 	}
-	defer systemImage.Close()
 
 	nodeParamsRaw, err := proto.Marshal(req.NodeParameters)
 	if err != nil {
@@ -143,9 +144,9 @@
 			Data:   128,
 		},
 		SystemImage:    systemImage,
-		EFIPayload:     FileSizedReader{efiPayload},
-		ABLoader:       bytes.NewReader(abloader),
-		NodeParameters: bytes.NewReader(nodeParamsRaw),
+		EFIPayload:     efiPayload,
+		ABLoader:       structfs.Bytes(abloader),
+		NodeParameters: structfs.Bytes(nodeParamsRaw),
 		Output:         rootDev,
 	}