diff --git a/node-tools/internal/runtime/own_account_test.go b/node-tools/internal/runtime/own_account_test.go
index eaf433d..a44d681 100644
--- a/node-tools/internal/runtime/own_account_test.go
+++ b/node-tools/internal/runtime/own_account_test.go
@@ -38,6 +38,26 @@ func TestNoBusWordReachesABundle(t *testing.T) {
 	}
 }
 
+// design 47 G §618, §519: the runtime's own fingerprint reaches no bundle; the fingerprint a module's composed words hold does.
+func TestTheRuntimesOwnFingerprintReachesNoBundle(t *testing.T) {
+	base := []string{"MESH_FINGERPRINT=runner-build", "PATH=/usr/bin"}
+	for name, c := range map[string]struct {
+		given map[string]string
+		want  string
+	}{
+		"composed with none sees none":   {nil, ""},
+		"composed with one sees its own": {map[string]string{"MESH_FINGERPRINT": "module-build"}, "MESH_FINGERPRINT=module-build"},
+	} {
+		env := strings.Join(BundleEnv(base, c.given, "telegram", "anchor"), "\n")
+		if strings.Contains(env, "runner-build") {
+			t.Errorf("%s: the runtime's own fingerprint reached the bundle: %s", name, env)
+		}
+		if c.want == "" && strings.Contains(env, "MESH_FINGERPRINT") || !strings.Contains(env, c.want) {
+			t.Errorf("%s: the environment is %s", name, env)
+		}
+	}
+}
+
 // A tool call reaches only a tool's subject: whatever key a caller names, it is never a seat's event, accept
 // or proof — so no tool call says a choice, a link or a code, or submits an ask, in anybody's name.
 func TestAToolCallNeverReachesASeatsEventAcceptOrProof(t *testing.T) {
diff --git a/node-tools/internal/runtime/runtime.go b/node-tools/internal/runtime/runtime.go
index f3bc178..bc982f5 100644
--- a/node-tools/internal/runtime/runtime.go
+++ b/node-tools/internal/runtime/runtime.go
@@ -59,6 +59,10 @@ type ListedTool struct {
 // NodeRuntimeModule is the module that is a machine's runtime, serving every module on it.
 const NodeRuntimeModule = "node-tools"
 
+// fingerprintEnv is the word the node-engine starts each process with, the fingerprint of the want it applies (mesh-sdk's
+// process.FingerprintEnv; this package imports no SDK): the runtime's own is no bundle's.
+const fingerprintEnv = "MESH_FINGERPRINT"
+
 // runtimeOnly are the words of the runtime's own environment no bundle is given.
 var runtimeOnly = map[string]bool{ToolEnv: true, ToolModules: true, "MESH_BROKER_FILE": true,
 	"MESH_BROKER_URL": true, "MESH_CONSOLE_LISTEN": true, LedgersFile: true}
@@ -1369,11 +1373,13 @@ func (b *moduleBus) bind(key string, stop func()) {
 // BundleEnv is what one module's bundle is started with: the runtime's environment without its own words,
 // the module's composed words over it, and the module's and machine's names. **No bus word reaches a
 // bundle** (security review of 2026-10-08): the credential and the bus's address are the runtime's, and a
-// bundle reaches the bus only through the runtime.
+// bundle reaches the bus only through the runtime. **The runtime's own fingerprint reaches none either**: a bundle reads
+// only the `MESH_FINGERPRINT` its module's composed words hold, the build the node-engine applied for that module, and with
+// none it has none (design 47 G §519, §618).
 func BundleEnv(base []string, given map[string]string, module, node string) []string {
 	words := map[string]string{}
 	for _, kv := range base {
-		if k, v, ok := strings.Cut(kv, "="); ok && !runtimeOnly[k] {
+		if k, v, ok := strings.Cut(kv, "="); ok && !runtimeOnly[k] && k != fingerprintEnv {
 			words[k] = v
 		}
 	}