diff --git a/modules/mesh-build-go/cmd/mesh-build-go/compose.go b/modules/mesh-build-go/cmd/mesh-build-go/compose.go
index 524ada97d..1d55fbf9d 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/compose.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/compose.go
@@ -50,7 +50,11 @@ func (m *Module) compose(ctx context.Context, fetch buildstep.StepFunc, a delive
 	if err != nil {
 		return nil, err
 	}
-	key := delivery.ComposerKey(repository, commit, job.Dir, job.Package, delivery.ToolchainUsed{Version: installed, Recipe: m.Recipe.Version()})
+	versions, err := sdkstep.PackagesArg(job.Fetch["packages"])
+	if err != nil {
+		return nil, buildstep.Refuse("the compose ask %s: %v", a.ID, err)
+	}
+	key := delivery.ComposerKey(repository, commit, job.Dir, job.Package, delivery.ToolchainUsed{Version: installed, Recipe: m.Recipe.Version()}, versions)
 	exe, built, err := m.composerOf(ctx, fetch, job, key)
 	if err != nil {
 		return nil, err
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/compose_test.go b/modules/mesh-build-go/cmd/mesh-build-go/compose_test.go
index 17dda5cd8..61cdf6f30 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/compose_test.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/compose_test.go
@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"os"
 	"path/filepath"
 	"slices"
@@ -64,7 +65,7 @@ func TestAKeptComposerIsRunWithTheManifestsFilled(t *testing.T) {
 	read, digests := indexerHolds(t, `{"module":"demo","version":"1"}`)
 	m.ReadManifest = read
 	a := composeAskOf(t, digests[0])
-	key := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()})
+	key := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()}, nil)
 	exe := m.composerPath(key)
 	if err := os.MkdirAll(filepath.Dir(exe), 0o700); err != nil {
 		t.Fatal(err)
@@ -95,13 +96,40 @@ func TestAKeptComposerIsRunWithTheManifestsFilled(t *testing.T) {
 	}
 }
 
+// 1921: the versions an ask names are an input of the composer it builds, so a composer kept for one set is not run for
+// another; an ask naming none keeps the key it always had.
+func TestAComposerIsKeptPerAskedVersions(t *testing.T) {
+	m := composeModule(t)
+	m.ReadManifest, _ = indexerHolds(t)
+	a := composeAskOf(t, "feedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeed")
+	tc := delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()}
+	plain := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, tc, nil)
+	a.Compose.Fetch["packages"] = map[string]any{"git.novox.be/novox/mesh-sdk/go": strings.Repeat("3", 40)}
+	named := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, tc, delivery.PackageVersions{"git.novox.be/novox/mesh-sdk/go": strings.Repeat("3", 40)})
+	if plain == named {
+		t.Fatal("the key ignores the versions")
+	}
+	// A composer kept under the key without versions is not used for the ask that names some: it is fetched.
+	os.MkdirAll(filepath.Dir(m.composerPath(plain)), 0o700)
+	os.WriteFile(m.composerPath(plain), []byte("#!/bin/sh\nexit 0\n"), 0o700)
+	fetched := false
+	fetch := func(context.Context, map[string]any) (any, error) {
+		fetched = true
+		return nil, errors.New("stop")
+	}
+	m.compose(context.Background(), fetch, a)
+	if !fetched {
+		t.Error("a composer built for no versions was run for an ask naming some")
+	}
+}
+
 // 1622: a manifest the indexer does not keep fails the ask, naming its digest; a fetched commit with no go.mod where
 // the ask builds fails it naming the directory, and its workspace is released.
 func TestAComposeAskFailsLoudly(t *testing.T) {
 	m := composeModule(t)
 	m.ReadManifest, _ = indexerHolds(t)
 	a := composeAskOf(t, "feedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeedfeed")
-	key := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()})
+	key := delivery.ComposerKey("novox/mesh-sdk", composeCommit, "go", composer.Package, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()}, nil)
 	os.MkdirAll(filepath.Dir(m.composerPath(key)), 0o700)
 	os.WriteFile(m.composerPath(key), []byte("#!/bin/sh\nexit 0\n"), 0o700)
 	if _, err := m.compose(context.Background(), nil, a); err == nil || !strings.Contains(err.Error(), "feedfeed") {
@@ -168,7 +196,7 @@ func TestAComposeAskBuildsTheNodeEnginesComposerAtItsRoot(t *testing.T) {
 		t.Fatal(err)
 	}
 	ans := out.(delivery.ComposeAnswer)
-	key := delivery.ComposerKey("novox/mesh-host", composeCommit, delivery.RootPath, nodeEngineComposer, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()})
+	key := delivery.ComposerKey("novox/mesh-host", composeCommit, delivery.RootPath, nodeEngineComposer, delivery.ToolchainUsed{Version: "go1.26.0", Recipe: m.Recipe.Version()}, nil)
 	var v composer.Verdict
 	if err := json.Unmarshal(ans.Verdict, &v); err != nil {
 		t.Fatal(err)