diff --git a/go/internal/client/setup/local_catalog.go b/go/internal/client/setup/local_catalog.go
new file mode 100644
index 0000000..0687ada
--- /dev/null
+++ b/go/internal/client/setup/local_catalog.go
@@ -0,0 +1,242 @@
+package setup
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	clientlayout "bd2server/internal/client/layout"
+)
+
+const (
+	remoteCatalogPrefix = "{BDNetwork.CdnInfo.Info}\\"
+	localCatalogPrefix  = "{UnityEngine.AddressableAssets.Addressables.RuntimePath}\\"
+	localCatalogBackup  = "catalog.json.bd2-before-local-sync"
+	maximumCatalogBytes = 128 << 20
+)
+
+func installCurrentLocalCatalog(gameDir, localRoot, bundleVersion string) error {
+	installation, err := clientlayout.Resolve(gameDir)
+	if err != nil {
+		return err
+	}
+	release := filepath.Join(filepath.Clean(localRoot), "ServerData", "StandaloneWindows64", "HD", bundleVersion)
+	source := filepath.Join(release, "catalog_alpha.json")
+	raw, err := readCatalog(source)
+	if err != nil {
+		return err
+	}
+	aa := filepath.Join(installation.Data, "StreamingAssets", "aa")
+	raw, err = localizeCatalog(raw, release, aa)
+	if err != nil {
+		return err
+	}
+	target := filepath.Join(aa, "catalog.json")
+	current, err := os.ReadFile(target)
+	if err != nil {
+		return fmt.Errorf("read built-in Addressables catalog: %w", err)
+	}
+	if bytes.Equal(current, raw) {
+		return nil
+	}
+	backup := filepath.Join(aa, localCatalogBackup)
+	if _, err := os.Stat(backup); errors.Is(err, os.ErrNotExist) {
+		if err := writeExclusiveFile(backup, current, 0o600); err != nil {
+			return fmt.Errorf("back up built-in Addressables catalog: %w", err)
+		}
+	} else if err != nil {
+		return fmt.Errorf("inspect built-in Addressables catalog backup: %w", err)
+	}
+	if err := replaceCatalog(target, raw); err != nil {
+		return fmt.Errorf("install current local Addressables catalog: %w", err)
+	}
+	return nil
+}
+
+func readCatalog(path string) ([]byte, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("open local ServerData catalog: %w", err)
+	}
+	defer file.Close()
+	raw, err := io.ReadAll(io.LimitReader(file, maximumCatalogBytes+1))
+	if err != nil {
+		return nil, fmt.Errorf("read local ServerData catalog: %w", err)
+	}
+	if len(raw) == 0 || len(raw) > maximumCatalogBytes {
+		return nil, errors.New("local ServerData catalog has an invalid size")
+	}
+	return raw, nil
+}
+
+func validateLocalCatalog(raw []byte, release string) error {
+	_, err := localizeCatalogIDs(raw, release)
+	return err
+}
+
+func localizeCatalog(raw []byte, release, aa string) ([]byte, error) {
+	document, ids, err := decodeCatalog(raw)
+	if err != nil {
+		return nil, err
+	}
+	remoteCount := 0
+	for index, internalID := range ids {
+		if strings.HasPrefix(internalID, remoteCatalogPrefix) {
+			relative, err := catalogBundlePath(internalID)
+			if err != nil {
+				return nil, err
+			}
+			source := filepath.Join(release, relative)
+			destination := filepath.Join(aa, relative)
+			if err := ensureCatalogBundleLink(source, destination); err != nil {
+				return nil, err
+			}
+			ids[index] = localCatalogPrefix + strings.ReplaceAll(filepath.ToSlash(relative), "/", "\\")
+			remoteCount++
+			continue
+		}
+		if strings.HasPrefix(internalID, localCatalogPrefix) {
+			relative := strings.TrimPrefix(internalID, localCatalogPrefix)
+			relative = filepath.FromSlash(strings.ReplaceAll(relative, "\\", "/"))
+			if info, err := os.Stat(filepath.Join(aa, relative)); err != nil || !info.Mode().IsRegular() {
+				return nil, fmt.Errorf("built-in Addressables catalog references a missing local bundle: %s", relative)
+			}
+		}
+	}
+	if remoteCount == 0 {
+		return nil, errors.New("local ServerData catalog has no CDN bundle entries")
+	}
+	encodedIDs, err := json.Marshal(ids)
+	if err != nil {
+		return nil, err
+	}
+	document["m_InternalIds"] = encodedIDs
+	localized, err := json.Marshal(document)
+	if err != nil {
+		return nil, fmt.Errorf("encode localized ServerData catalog: %w", err)
+	}
+	return localized, nil
+}
+
+func localizeCatalogIDs(raw []byte, release string) ([]string, error) {
+	_, ids, err := decodeCatalog(raw)
+	if err != nil {
+		return nil, err
+	}
+	remoteCount := 0
+	for _, internalID := range ids {
+		if !strings.HasPrefix(internalID, remoteCatalogPrefix) {
+			continue
+		}
+		relative, err := catalogBundlePath(internalID)
+		if err != nil {
+			return nil, err
+		}
+		if info, err := os.Stat(filepath.Join(release, relative)); err != nil || !info.Mode().IsRegular() {
+			return nil, fmt.Errorf("local ServerData catalog references a missing bundle: %s", relative)
+		}
+		remoteCount++
+	}
+	if remoteCount == 0 {
+		return nil, errors.New("local ServerData catalog has no CDN bundle entries")
+	}
+	return ids, nil
+}
+
+func decodeCatalog(raw []byte) (map[string]json.RawMessage, []string, error) {
+	var document map[string]json.RawMessage
+	decoder := json.NewDecoder(bytes.NewReader(raw))
+	if err := decoder.Decode(&document); err != nil {
+		return nil, nil, fmt.Errorf("decode local ServerData catalog: %w", err)
+	}
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		return nil, nil, errors.New("local ServerData catalog must contain exactly one JSON object")
+	}
+	var ids []string
+	if err := json.Unmarshal(document["m_InternalIds"], &ids); err != nil || len(ids) == 0 {
+		return nil, nil, errors.New("local ServerData catalog has no valid internal IDs")
+	}
+	return document, ids, nil
+}
+
+func ensureCatalogBundleLink(source, destination string) error {
+	sourceInfo, err := os.Stat(source)
+	if err != nil || !sourceInfo.Mode().IsRegular() {
+		return fmt.Errorf("local ServerData catalog references a missing bundle: %s", source)
+	}
+	if destinationInfo, err := os.Stat(destination); err == nil {
+		if !destinationInfo.Mode().IsRegular() || !os.SameFile(sourceInfo, destinationInfo) {
+			return fmt.Errorf("game Addressables bundle conflicts with the selected local release: %s", destination)
+		}
+		return nil
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("inspect game Addressables bundle: %w", err)
+	}
+	if err := os.MkdirAll(filepath.Dir(destination), 0o755); err != nil {
+		return fmt.Errorf("create game Addressables bundle directory: %w", err)
+	}
+	if err := os.Link(source, destination); err != nil {
+		return fmt.Errorf("hard-link local bundle without duplicating it (keep the game and local resources on the same filesystem): %w", err)
+	}
+	return nil
+}
+
+func catalogBundlePath(internalID string) (string, error) {
+	parts := strings.Split(strings.ReplaceAll(internalID, "\\", "/"), "/")
+	if len(parts) < 5 {
+		return "", fmt.Errorf("local ServerData catalog has an invalid CDN path: %q", internalID)
+	}
+	parts = parts[4:]
+	for _, part := range parts {
+		if part == "" || part == "." || part == ".." || strings.ContainsAny(part, `:{}`) {
+			return "", fmt.Errorf("local ServerData catalog has an unsafe bundle path: %q", internalID)
+		}
+	}
+	relative := filepath.Join(parts...)
+	if !strings.EqualFold(filepath.Ext(relative), ".bundle") {
+		return "", fmt.Errorf("local ServerData catalog CDN path is not a bundle: %q", internalID)
+	}
+	return relative, nil
+}
+
+func writeExclusiveFile(path string, data []byte, mode os.FileMode) error {
+	file, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, mode)
+	if err != nil {
+		return err
+	}
+	if _, err = file.Write(data); err == nil {
+		err = file.Sync()
+	}
+	if closeErr := file.Close(); err == nil {
+		err = closeErr
+	}
+	return err
+}
+
+func replaceCatalog(path string, data []byte) error {
+	temporary, err := os.CreateTemp(filepath.Dir(path), ".catalog-local-*.json")
+	if err != nil {
+		return err
+	}
+	temporaryPath := temporary.Name()
+	defer os.Remove(temporaryPath)
+	if err = temporary.Chmod(0o600); err == nil {
+		_, err = temporary.Write(data)
+	}
+	if err == nil {
+		err = temporary.Sync()
+	}
+	if closeErr := temporary.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		return err
+	}
+	return os.Rename(temporaryPath, path)
+}
diff --git a/go/internal/client/setup/local_catalog_test.go b/go/internal/client/setup/local_catalog_test.go
new file mode 100644
index 0000000..6a34669
--- /dev/null
+++ b/go/internal/client/setup/local_catalog_test.go
@@ -0,0 +1,99 @@
+package setup
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestValidateLocalCatalogRequiresEveryRemoteBundle(t *testing.T) {
+	release := t.TempDir()
+	path := filepath.Join("nested", "current.bundle")
+	if err := os.MkdirAll(filepath.Join(release, "nested"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(release, path), []byte("bundle"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	raw, err := json.Marshal(map[string]any{"m_InternalIds": []string{
+		remoteCatalogPrefix + `StandaloneWindows64\HD\version\nested/current.bundle`,
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := validateLocalCatalog(raw, release); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Remove(filepath.Join(release, path)); err != nil {
+		t.Fatal(err)
+	}
+	if err := validateLocalCatalog(raw, release); err == nil {
+		t.Fatal("catalog with missing bundle unexpectedly passed")
+	}
+}
+
+func TestCatalogBundlePathRejectsTraversal(t *testing.T) {
+	if _, err := catalogBundlePath(remoteCatalogPrefix + `StandaloneWindows64\HD\version\..\escape.bundle`); err == nil {
+		t.Fatal("catalog traversal path unexpectedly passed")
+	}
+}
+
+func TestReplaceCatalogReplacesExistingFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "catalog.json")
+	if err := os.WriteFile(path, []byte("old"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := replaceCatalog(path, []byte("new")); err != nil {
+		t.Fatal(err)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != "new" {
+		t.Fatalf("catalog=%q", got)
+	}
+}
+
+func TestLocalizeCatalogPreservesMetadataAndCreatesHardLink(t *testing.T) {
+	release := t.TempDir()
+	aa := t.TempDir()
+	relative := filepath.Join("nested", "current.bundle")
+	if err := os.MkdirAll(filepath.Join(release, "nested"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	source := filepath.Join(release, relative)
+	if err := os.WriteFile(source, []byte("bundle"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	raw, err := json.Marshal(map[string]any{
+		"m_BuildResultHash": "current-metadata",
+		"m_InternalIds": []string{
+			remoteCatalogPrefix + `StandaloneWindows64\HD\version\nested/current.bundle`,
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	localized, err := localizeCatalog(raw, release, aa)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Contains(localized, []byte(`"m_BuildResultHash":"current-metadata"`)) ||
+		!bytes.Contains(localized, []byte(`Addressables.RuntimePath`)) {
+		t.Fatalf("localized catalog=%s", localized)
+	}
+	sourceInfo, err := os.Stat(source)
+	if err != nil {
+		t.Fatal(err)
+	}
+	destinationInfo, err := os.Stat(filepath.Join(aa, relative))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !os.SameFile(sourceInfo, destinationInfo) {
+		t.Fatal("localized bundle is not a hard link to the selected release")
+	}
+}
diff --git a/go/internal/client/setup/setup.go b/go/internal/client/setup/setup.go
index 50cb622..7d213a8 100644
--- a/go/internal/client/setup/setup.go
+++ b/go/internal/client/setup/setup.go
@@ -82,7 +82,16 @@ func SaveSettings(gameDir string, settings clientconfig.Settings, versions clien
 	if _, err := Inspect(gameDir, versions); err != nil {
 		return clientconfig.Settings{}, err
 	}
-	return clientconfig.Save(gameDir, settings)
+	normalized, err := clientconfig.Normalize(settings)
+	if err != nil {
+		return clientconfig.Settings{}, err
+	}
+	if normalized.CDNMode == clientconfig.CDNLocal {
+		if err := installCurrentLocalCatalog(gameDir, normalized.LocalResourceDirectory, versions.BundleVersion); err != nil {
+			return clientconfig.Settings{}, err
+		}
+	}
+	return clientconfig.Save(gameDir, normalized)
 }
 
 func Patch(gameDir string, settings clientconfig.Settings, versions clientconfig.ReleaseVersions) (introdb.Result, error) {
@@ -116,7 +125,7 @@ func InstallPlugins(
 	if !status.BepInEx {
 		return InstallResult{}, fmt.Errorf("BepInEx is not installed; install it from %s before installing the plugins", plugin.BepInExReleasesURL)
 	}
-	if _, err := clientconfig.Save(gameDir, settings); err != nil {
+	if _, err := SaveSettings(gameDir, settings, versions); err != nil {
 		return InstallResult{}, err
 	}
 	localSource, err := plugin.ResolvePackaged(plugin.LocalIdentity, localIdentitySource)