diff --git a/modules/mesh-build-node/cmd/mesh-build-node/build.go b/modules/mesh-build-node/cmd/mesh-build-node/build.go
index 7788455d..3c6e5776 100644
--- a/modules/mesh-build-node/cmd/mesh-build-node/build.go
+++ b/modules/mesh-build-node/cmd/mesh-build-node/build.go
@@ -21,10 +21,6 @@ import (
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
-// launcherSuffix is what an entrypoint's launcher is called beside it: index.js is started as index.serve.mjs
-// (novox/hq ADR 0193).
-const launcherSuffix = ".serve.mjs"
-
 // Out is where a bundle's compiled files go in the module's directory (builder toolchain.go:118).
 func Out(artifact string) string { return ".mesh-build/" + artifact }
 
@@ -216,15 +212,12 @@ func (m *Module) bundle(ctx context.Context, root string, publish bool, dir stri
 }
 
 // writeLaunchers writes, beside every entrypoint, an executable that imports the entrypoint and serves what it
-// registered over MCP on stdio (builder.go:1926-1956; novox/hq ADR 0193). Its answer is each entrypoint's launcher,
-// relative to the bundle's root.
+// registered over MCP on stdio (builder.go:1926-1956; novox/hq ADR 0193). Which entrypoint gets which launcher is
+// mesh-sdk's one rule, buildstep.Launchers, which the controller reads a bundle by (R4e). Its answer is each
+// entrypoint's launcher, relative to the bundle's root.
 func writeLaunchers(root string, a artifact) (map[string]string, error) {
 	out := map[string]string{}
-	for _, entry := range a.Entrypoints {
-		if !strings.HasSuffix(entry, ".js") {
-			continue
-		}
-		launcher := strings.TrimSuffix(entry, ".js") + launcherSuffix
+	for entry, launcher := range buildstep.Launchers(a.Language, a.Entrypoints) {
 		body := "#!/usr/bin/env node\n" +
 			"// Written by the mesh's builder (novox/hq ADR 0193): serve what " + entry + " registers,\n" +
 			"// over MCP on stdio, as the module the node's runtime names in MESH_SERVED_MODULE.\n" +
diff --git a/modules/mesh-build-node/cmd/mesh-build-node/build_test.go b/modules/mesh-build-node/cmd/mesh-build-node/build_test.go
index fb45a6e4..0165c9bd 100644
--- a/modules/mesh-build-node/cmd/mesh-build-node/build_test.go
+++ b/modules/mesh-build-node/cmd/mesh-build-node/build_test.go
@@ -6,12 +6,14 @@ import (
 	"compress/gzip"
 	"context"
 	"io"
+	"maps"
 	"os"
 	"path/filepath"
 	"slices"
 	"strings"
 	"testing"
 
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/forgekey"
 )
 
@@ -252,3 +254,16 @@ func TestTheBuildRunsWithThePackagesTwoLevelsAboveTheModule(t *testing.T) {
 		}
 	}
 }
+
+// R4e: the launchers a build writes are mesh-sdk's one rule (buildstep.Launchers), the names the controller reads a bundle
+// by; an entrypoint that is not JavaScript gets none.
+func TestTheLaunchersAreTheSDKsRule(t *testing.T) {
+	a := artifact{Language: "typescript", Entrypoints: []string{"tools/index.js", "web/server.js", "assets/x.css"}}
+	got, err := writeLaunchers(t.TempDir(), a)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := buildstep.Launchers(a.Language, a.Entrypoints); !maps.Equal(got, want) || len(got) != 2 {
+		t.Errorf("launchers %v, mesh-sdk's rule %v", got, want)
+	}
+}
diff --git a/modules/mesh-build-node/cmd/mesh-build-node/recipe.go b/modules/mesh-build-node/cmd/mesh-build-node/recipe.go
index c83fead8..ea3a8eb7 100644
--- a/modules/mesh-build-node/cmd/mesh-build-node/recipe.go
+++ b/modules/mesh-build-node/cmd/mesh-build-node/recipe.go
@@ -14,7 +14,7 @@ import (
 
 // RecipeSteps is the recipe's own version: changed whenever the steps of fetch, test or build change in a way that
 // can change what they produce (ADR 0405 §7). It is one of the two values the recipe version hashes.
-const RecipeSteps = "1"
+const RecipeSteps = "2" // 2: a member is built against the SDK its own lock names (R4e, the lead's decision L10)
 
 // Recipe is every value that makes up the recipe version.
 type Recipe struct {