diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3b6dea0
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,9 @@
+# Local Go build cache
+.cache/
+
+# Built tool output
+/tools/nwn-tool
+
+# OS/editor noise
+.DS_Store
+Thumbs.db
diff --git a/internal/erf/erf.go b/internal/erf/erf.go
index 07dda40..34cebff 100644
--- a/internal/erf/erf.go
+++ b/internal/erf/erf.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"os"
 	"sort"
 	"strings"
 )
@@ -24,9 +25,11 @@ type Archive struct {
 }
 
 type Resource struct {
-	Name string
-	Type uint16
-	Data []byte
+	Name       string
+	Type       uint16
+	Data       []byte
+	SourcePath string
+	Size       int64
 }
 
 type header struct {
@@ -139,7 +142,7 @@ func New(fileType string, resources []Resource) Archive {
 }
 
 func ArchiveSize(resources []Resource) int64 {
-	return int64(headerSize + len(resources)*24 + len(resources)*8 + totalResourceBytes(resources))
+	return int64(headerSize+len(resources)*24+len(resources)*8) + totalResourceBytes(resources)
 }
 
 func Write(w io.Writer, archive Archive) error {
@@ -154,28 +157,30 @@ func Write(w io.Writer, archive Archive) error {
 	entries := make([]resourceEntry, 0, len(archive.Resources))
 
 	dataOffset := uint32(headerSize + len(archive.Resources)*24 + len(archive.Resources)*8)
-	data := bytes.Buffer{}
-
 	for index, resource := range archive.Resources {
 		if len(resource.Name) > 16 {
 			return fmt.Errorf("resource %q exceeds 16-byte resref limit", resource.Name)
 		}
+		size, err := payloadSize(resource)
+		if err != nil {
+			return err
+		}
+		if size > int64(^uint32(0)) {
+			return fmt.Errorf("resource %q exceeds 4 GiB resource size limit", resource.Name)
+		}
 
 		entry := resourceEntry{
-			Offset: dataOffset + uint32(data.Len()),
-			Size:   uint32(len(resource.Data)),
+			Offset: dataOffset,
+			Size:   uint32(size),
 		}
 		entries = append(entries, entry)
+		dataOffset += uint32(size)
 
 		var key keyEntry
 		copy(key.ResRef[:], []byte(resource.Name))
 		key.ResourceID = uint32(index)
 		key.ResourceType = resource.Type
 		keys = append(keys, key)
-
-		if _, err := data.Write(resource.Data); err != nil {
-			return err
-		}
 	}
 
 	hdr := header{
@@ -192,22 +197,21 @@ func Write(w io.Writer, archive Archive) error {
 	copy(hdr.FileType[:], []byte(padFour(archive.FileType)))
 	copy(hdr.Version[:], []byte(padFour(archive.Version)))
 
-	var buf bytes.Buffer
-	if err := binary.Write(&buf, binary.LittleEndian, hdr); err != nil {
+	if err := binary.Write(w, binary.LittleEndian, hdr); err != nil {
 		return err
 	}
-	if err := binary.Write(&buf, binary.LittleEndian, keys); err != nil {
+	if err := binary.Write(w, binary.LittleEndian, keys); err != nil {
 		return err
 	}
-	if err := binary.Write(&buf, binary.LittleEndian, entries); err != nil {
+	if err := binary.Write(w, binary.LittleEndian, entries); err != nil {
 		return err
 	}
-	if _, err := buf.Write(data.Bytes()); err != nil {
-		return err
+	for _, resource := range archive.Resources {
+		if err := writeResourceData(w, resource); err != nil {
+			return err
+		}
 	}
-
-	_, err := w.Write(buf.Bytes())
-	return err
+	return nil
 }
 
 func Read(r io.Reader) (Archive, error) {
@@ -260,6 +264,7 @@ func Read(r io.Reader) (Archive, error) {
 			Name: resref,
 			Type: key.ResourceType,
 			Data: payload,
+			Size: int64(entry.Size),
 		})
 	}
 
@@ -288,10 +293,51 @@ func padFour(value string) string {
 	return value + strings.Repeat(" ", 4-len(value))
 }
 
-func totalResourceBytes(resources []Resource) int {
-	total := 0
+func totalResourceBytes(resources []Resource) int64 {
+	var total int64
 	for _, resource := range resources {
-		total += len(resource.Data)
+		switch {
+		case resource.Size > 0:
+			total += resource.Size
+		default:
+			total += int64(len(resource.Data))
+		}
 	}
 	return total
 }
+
+func payloadSize(resource Resource) (int64, error) {
+	if resource.Size > 0 {
+		return resource.Size, nil
+	}
+	if resource.SourcePath != "" && len(resource.Data) == 0 {
+		info, err := os.Stat(resource.SourcePath)
+		if err != nil {
+			return 0, fmt.Errorf("stat resource %q: %w", resource.SourcePath, err)
+		}
+		return info.Size(), nil
+	}
+	return int64(len(resource.Data)), nil
+}
+
+func writeResourceData(w io.Writer, resource Resource) error {
+	if len(resource.Data) > 0 || resource.SourcePath == "" {
+		_, err := w.Write(resource.Data)
+		return err
+	}
+
+	file, err := os.Open(resource.SourcePath)
+	if err != nil {
+		return fmt.Errorf("open resource %q: %w", resource.SourcePath, err)
+	}
+	defer file.Close()
+
+	written, err := io.Copy(w, file)
+	if err != nil {
+		return fmt.Errorf("copy resource %q: %w", resource.SourcePath, err)
+	}
+	if resource.Size > 0 && written != resource.Size {
+		return fmt.Errorf("copy resource %q: expected %d bytes, wrote %d", resource.SourcePath, resource.Size, written)
+	}
+	return nil
+}
diff --git a/internal/pipeline/build.go b/internal/pipeline/build.go
index 1a194ac..d9246ff 100644
--- a/internal/pipeline/build.go
+++ b/internal/pipeline/build.go
@@ -45,12 +45,11 @@ type assetResource struct {
 }
 
 type hakChunk struct {
-	Config    project.HAKConfig
-	Index     int
-	Name      string
-	Assets    []assetResource
-	Size      int64
-	Resources []erf.Resource
+	Config project.HAKConfig
+	Index  int
+	Name   string
+	Assets []assetResource
+	Size   int64
 }
 
 func Build(p *project.Project) (BuildResult, error) {
@@ -132,7 +131,7 @@ func BuildHAKs(p *project.Project) (BuildResult, error) {
 		if err != nil {
 			return BuildResult{}, fmt.Errorf("create hak archive: %w", err)
 		}
-		if err := erf.Write(hakOutput, erf.New("HAK ", chunk.Resources)); err != nil {
+		if err := erf.Write(hakOutput, erf.New("HAK ", resourceSlice(chunk.Assets))); err != nil {
 			hakOutput.Close()
 			return BuildResult{}, fmt.Errorf("write hak archive: %w", err)
 		}
@@ -198,7 +197,7 @@ func collectAssetResources(p *project.Project) ([]assetResource, error) {
 
 	for _, rel := range p.Inventory.AssetFiles {
 		abs := filepath.Join(p.AssetsDir(), filepath.FromSlash(rel))
-		resource, err := rawResource(abs)
+		resource, err := pathResource(abs)
 		if err != nil {
 			return nil, err
 		}
@@ -276,6 +275,25 @@ func resourceFromJSON(path string, moduleHakOrder []string) (erf.Resource, error
 	}, nil
 }
 
+func pathResource(path string) (erf.Resource, error) {
+	extension := strings.TrimPrefix(strings.ToLower(filepath.Ext(path)), ".")
+	resourceType, ok := erf.ResourceTypeForExtension(extension)
+	if !ok {
+		return erf.Resource{}, fmt.Errorf("unsupported resource extension %q", filepath.Ext(path))
+	}
+	name := strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
+	info, err := os.Stat(path)
+	if err != nil {
+		return erf.Resource{}, fmt.Errorf("stat %s: %w", path, err)
+	}
+	return erf.Resource{
+		Name:       name,
+		Type:       resourceType,
+		SourcePath: path,
+		Size:       info.Size(),
+	}, nil
+}
+
 func rawResource(path string) (erf.Resource, error) {
 	extension := strings.TrimPrefix(strings.ToLower(filepath.Ext(path)), ".")
 	resourceType, ok := erf.ResourceTypeForExtension(extension)
@@ -317,11 +335,10 @@ func planHAKChunks(p *project.Project, assets []assetResource) ([]hakChunk, erro
 				Name:     p.Config.Module.ResRef,
 				Priority: 1,
 			},
-			Index:     1,
-			Name:      p.Config.Module.ResRef,
-			Size:      erf.ArchiveSize(resourceSlice(assets)),
-			Assets:    assets,
-			Resources: resourceSlice(assets),
+			Index:  1,
+			Name:   p.Config.Module.ResRef,
+			Size:   erf.ArchiveSize(resourceSlice(assets)),
+			Assets: assets,
 		}
 		return []hakChunk{chunk}, nil
 	}
@@ -373,12 +390,11 @@ func splitHAKGroup(cfg project.HAKConfig, assets []assetResource) ([]hakChunk, e
 	maxBytes := cfg.MaxBytes
 	if maxBytes == 0 {
 		chunk := hakChunk{
-			Config:    cfg,
-			Index:     1,
-			Name:      cfg.Name,
-			Assets:    assets,
-			Resources: resourceSlice(assets),
-			Size:      erf.ArchiveSize(resourceSlice(assets)),
+			Config: cfg,
+			Index:  1,
+			Name:   cfg.Name,
+			Assets: assets,
+			Size:   erf.ArchiveSize(resourceSlice(assets)),
 		}
 		if err := ensureUniqueChunkResources(chunk); err != nil {
 			return nil, err
@@ -398,14 +414,12 @@ func splitHAKGroup(cfg project.HAKConfig, assets []assetResource) ([]hakChunk, e
 				return nil, fmt.Errorf("asset %s alone exceeds max_bytes for hak %s", asset.Rel, cfg.Name)
 			}
 			current.Assets = candidateAssets
-			current.Resources = candidateResources
 			current.Size = candidateSize
 			continue
 		}
 
 		if candidateSize <= maxBytes {
 			current.Assets = candidateAssets
-			current.Resources = candidateResources
 			current.Size = candidateSize
 			continue
 		}
@@ -421,11 +435,10 @@ func splitHAKGroup(cfg project.HAKConfig, assets []assetResource) ([]hakChunk, e
 		chunks = append(chunks, current)
 
 		current = hakChunk{
-			Config:    cfg,
-			Index:     current.Index + 1,
-			Assets:    []assetResource{asset},
-			Resources: []erf.Resource{asset.Resource},
-			Size:      erf.ArchiveSize([]erf.Resource{asset.Resource}),
+			Config: cfg,
+			Index:  current.Index + 1,
+			Assets: []assetResource{asset},
+			Size:   erf.ArchiveSize([]erf.Resource{asset.Resource}),
 		}
 		if current.Size > maxBytes {
 			return nil, fmt.Errorf("asset %s alone exceeds max_bytes for hak %s", asset.Rel, cfg.Name)
diff --git a/tools/nwn-tool b/tools/nwn-tool
deleted file mode 100755
index 9b1cf93..0000000
Binary files a/tools/nwn-tool and /dev/null differ