diff --git a/go/packageguard/packageversion_test.go b/go/packageguard/packageversion_test.go
new file mode 100644
index 0000000..2ec2d8c
--- /dev/null
+++ b/go/packageguard/packageversion_test.go
@@ -0,0 +1,104 @@
+package packageguard
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"testing"
+)
+
+// The registry refuses a second, different package under one version
+// ("version taken", issues 1899 and 1331). This guard fails before a merge when
+// what npm packs changes while the version stays: package-version.sum holds the
+// version and a sha256 over the inputs of the packed dist (package.json without
+// its version, src/, tsconfig.json) and of the README npm always packs.
+// The lock file is not packed, so it is not hashed.
+
+const sumFile = "package-version.sum"
+
+func packedInputs(root string) (version, sum string, err error) {
+	raw, err := os.ReadFile(filepath.Join(root, "package.json"))
+	if err != nil {
+		return "", "", err
+	}
+	var pkg map[string]any
+	if err := json.Unmarshal(raw, &pkg); err != nil {
+		return "", "", err
+	}
+	version, _ = pkg["version"].(string)
+	delete(pkg, "version")
+	canon, err := json.Marshal(pkg) // map keys are sorted: stable bytes
+	if err != nil {
+		return "", "", err
+	}
+	files := map[string][]byte{"package.json": canon}
+	for _, name := range []string{"tsconfig.json", "README.md"} {
+		b, err := os.ReadFile(filepath.Join(root, name))
+		if err != nil {
+			return "", "", err
+		}
+		files[name] = b
+	}
+	err = filepath.WalkDir(filepath.Join(root, "src"), func(p string, d fs.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		b, err := os.ReadFile(p)
+		if err != nil {
+			return err
+		}
+		rel, _ := filepath.Rel(root, p)
+		files[filepath.ToSlash(rel)] = b
+		return nil
+	})
+	if err != nil {
+		return "", "", err
+	}
+	names := make([]string, 0, len(files))
+	for n := range files {
+		names = append(names, n)
+	}
+	sort.Strings(names)
+	h := sha256.New()
+	for _, n := range names {
+		fmt.Fprintf(h, "%s\x00%d\x00", n, len(files[n]))
+		h.Write(files[n])
+	}
+	return version, hex.EncodeToString(h.Sum(nil)), nil
+}
+
+func TestPackageVersionMatchesPackedInputs(t *testing.T) {
+	root := "../.."
+	if r := os.Getenv("MESH_SDK_ROOT"); r != "" {
+		root = r
+	}
+	version, sum, err := packedInputs(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	line := version + " " + sum + "\n"
+	if os.Getenv("UPDATE_PACKAGE_VERSION_SUM") != "" {
+		if err := os.WriteFile(filepath.Join(root, sumFile), []byte(line), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return
+	}
+	raw, err := os.ReadFile(filepath.Join(root, sumFile))
+	if err != nil {
+		t.Fatalf("%s is missing: %v", sumFile, err)
+	}
+	recVersion, recSum, _ := strings.Cut(strings.TrimSpace(string(raw)), " ")
+	switch {
+	case recVersion == version && recSum == sum:
+	case recVersion == version:
+		t.Fatalf("what npm packs for @novox/mesh-sdk changed while its version stayed %s: the registry would refuse a second, different %s. Raise @novox/mesh-sdk's version (package.json and package-lock.json) and update %s (UPDATE_PACKAGE_VERSION_SUM=1 go test -run TestPackageVersionMatchesPackedInputs in go/packageguard)", version, version, sumFile)
+	default:
+		t.Fatalf("package.json says %s but %s records %s: update %s (UPDATE_PACKAGE_VERSION_SUM=1 go test -run TestPackageVersionMatchesPackedInputs in go/packageguard)", version, sumFile, recVersion, sumFile)
+	}
+}
diff --git a/package-lock.json b/package-lock.json
index 781fd1a..acf4da6 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@novox/mesh-sdk",
-  "version": "0.1.16",
+  "version": "0.1.17",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@novox/mesh-sdk",
-      "version": "0.1.16",
+      "version": "0.1.17",
       "devDependencies": {
         "@types/node": "^22.0.0",
         "typescript": "^5.6.0"
diff --git a/package-version.sum b/package-version.sum
new file mode 100644
index 0000000..6925adf
--- /dev/null
+++ b/package-version.sum
@@ -0,0 +1 @@
+0.1.17 90cca0bf1acfb386d66ccddb9f612703cf8f0205791b846982a524d0044aa0fb
diff --git a/package.json b/package.json
index e88f736..cd0af54 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@novox/mesh-sdk",
-  "version": "0.1.16",
+  "version": "0.1.17",
   "description": "The stable spine a Novox Mesh module's own code builds against.",
   "type": "module",
   "exports": {