diff --git a/internal/compose/composed.go b/internal/compose/composed.go
index 5bdc1c0a..7516d9e3 100644
--- a/internal/compose/composed.go
+++ b/internal/compose/composed.go
@@ -388,8 +388,8 @@ func ToolsRunning(running []engcomp.Composed) map[string][]catalogue.Bundle {
 		}
 		var own map[string]string
 		for w, v := range words[module] {
-			if w == catalogue.FilesOwnedPaths || w == catalogue.ReadsSecretPlaces {
-				continue // the mesh's to say, composed again
+			if w == catalogue.FilesOwnedPaths || w == catalogue.ReadsSecretPlaces || w == engcomp.FingerprintVar {
+				continue // the mesh's to say, composed again (the fingerprint is the want's, §519)
 			}
 			if own == nil {
 				own = map[string]string{}
diff --git a/internal/compose/composed_test.go b/internal/compose/composed_test.go
index c33c7490..6abb069e 100644
--- a/internal/compose/composed_test.go
+++ b/internal/compose/composed_test.go
@@ -180,7 +180,12 @@ func TestCompositionsAreTheDeclarationSplitByModule(t *testing.T) {
 				}
 			}
 		}
-		if env[catalogue.RuntimeToolModules] != served || env[catalogue.RuntimeToolEnv] != `{"lamp":{"LAMP_CONF":"/var/lib/lamp/conf"}}` {
+		// §519: the words each bundle's module is given hold the fingerprint of the want it applies, where there is one.
+		words := `{"lamp":{"LAMP_CONF":"/var/lib/lamp/conf"}}`
+		if fp := row.fps["lamp"]; fp != "" {
+			words = `{"lamp":{"LAMP_CONF":"/var/lib/lamp/conf","MESH_FINGERPRINT":"` + fp + `"}}`
+		}
+		if env[catalogue.RuntimeToolModules] != served || env[catalogue.RuntimeToolEnv] != words {
 			t.Errorf("%s: the runtime serves %v with %v, want what runs of lamp, %s", row.name,
 				env[catalogue.RuntimeToolModules], env[catalogue.RuntimeToolEnv], served)
 		}
diff --git a/internal/compositions/compare_test.go b/internal/compositions/compare_test.go
index a4987123..434deff4 100644
--- a/internal/compositions/compare_test.go
+++ b/internal/compositions/compare_test.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	seat "git.novox.be/novox/mesh-contracts/go/seats/nodeengine"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"slices"
 	"strings"
 	"testing"
@@ -203,6 +204,26 @@ func TestComparingCompositions(t *testing.T) {
 			t.Errorf("the node's own carries %s: %s", FingerprintVar, raw)
 		}
 	}
+
+	// §519, §618: the tool runner's process hands each bundle's module its own want's fingerprint in the words of its
+	// bundles, a module with bundles and no words included, and the runner's own fingerprint reaches no other module's.
+	fpLamp, fpBare := "src2:"+strings.Repeat("1", 64), "src2:"+strings.Repeat("2", 64)
+	runner, err := Split("novox", []json.RawMessage{json.RawMessage(`{"id":"r","type":"process","module":"nats","run":["x"],"env":{` +
+		`"` + catalogue.RuntimeToolModules + `":"bare=/b/x,lamp=/l/y","` + catalogue.RuntimeToolEnv + `":"{\"lamp\":{\"LAMP_CONF\":\"/c\"}}"}}`)},
+		map[string]string{"nats": fp, "lamp": fpLamp, "bare": fpBare}, nil, NodeOwn{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var proc struct{ Env map[string]string }
+	_ = json.Unmarshal(runner[mustKey(t, "novox", "nats", fp)].Resources[0], &proc)
+	var given map[string]map[string]string
+	if err := json.Unmarshal([]byte(proc.Env[catalogue.RuntimeToolEnv]), &given); err != nil {
+		t.Fatal(err)
+	}
+	if given["lamp"][FingerprintVar] != fpLamp || given["lamp"]["LAMP_CONF"] != "/c" || given["bare"][FingerprintVar] != fpBare ||
+		len(given["nats"]) != 0 || proc.Env[FingerprintVar] != fp {
+		t.Errorf("the bundles' words are %v and the runner's env %v", given, proc.Env)
+	}
 }
 
 func mustKey(t *testing.T, node, module, fp string) string {
diff --git a/internal/compositions/composed.go b/internal/compositions/composed.go
index 924a0eeb..a2d5223f 100644
--- a/internal/compositions/composed.go
+++ b/internal/compositions/composed.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"regexp"
+	"strings"
 
 	"git.novox.be/novox/mesh-contracts/go/clients/nodeengineclient"
 	"git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogclient"
@@ -239,6 +240,9 @@ func Split(node string, resources []json.RawMessage, fps map[string]string, fill
 			if raw, err = withFingerprint(raw, head.Type, fps[head.Module]); err != nil {
 				return nil, err
 			}
+			if raw, err = withBundleFingerprints(raw, head.Type, fps); err != nil {
+				return nil, err
+			}
 		}
 		c := out[key]
 		c.Resources = append(c.Resources, raw)
@@ -286,3 +290,62 @@ func withFingerprint(raw json.RawMessage, kind, fp string) (json.RawMessage, err
 	fields["env"] = body
 	return json.Marshal(fields)
 }
+
+// withBundleFingerprints is raw, when it is a process whose env hands tools bundles their words (catalogue.RuntimeToolEnv),
+// with each module's words holding FingerprintVar set to that module's fingerprint in fps: a bundle reads the fingerprint of
+// its own module's want from the environment the tool runner starts it with (design 47 G §519). A module fps names no
+// fingerprint for keeps its words, and the runner's own fingerprint reaches no bundle but its own module's (§618).
+func withBundleFingerprints(raw json.RawMessage, kind string, fps map[string]string) (json.RawMessage, error) {
+	if kind != string(declaration.TypeProcess) {
+		return raw, nil
+	}
+	var fields map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &fields); err != nil {
+		return nil, fmt.Errorf("compositions: a %s resource is not JSON: %w", kind, err)
+	}
+	var env map[string]string
+	if had, ok := fields["env"]; !ok || json.Unmarshal(had, &env) != nil || env[catalogue.RuntimeToolModules] == "" {
+		return raw, nil
+	}
+	given := map[string]map[string]string{}
+	if had := env[catalogue.RuntimeToolEnv]; had != "" {
+		if err := json.Unmarshal([]byte(had), &given); err != nil {
+			return nil, fmt.Errorf("compositions: the %s of a process is not words by module: %w", catalogue.RuntimeToolEnv, err)
+		}
+	}
+	for module, words := range given {
+		if fp := fps[module]; fp != "" {
+			if words == nil {
+				words = map[string]string{}
+				given[module] = words
+			}
+			words[FingerprintVar] = fp
+		}
+	}
+	for module, fp := range fps { // a module with bundles and no words of its own still reads its fingerprint
+		if _, has := given[module]; !has && fp != "" && hasLoadedBundle(env, module) {
+			given[module] = map[string]string{FingerprintVar: fp}
+		}
+	}
+	body, err := json.Marshal(given)
+	if err != nil {
+		return nil, err
+	}
+	env[catalogue.RuntimeToolEnv] = string(body)
+	envBody, err := json.Marshal(env)
+	if err != nil {
+		return nil, err
+	}
+	fields["env"] = envBody
+	return json.Marshal(fields)
+}
+
+// hasLoadedBundle is whether the runtime's served list (catalogue.RuntimeToolModules, `module=path` entries) names a bundle of module.
+func hasLoadedBundle(env map[string]string, module string) bool {
+	for _, entry := range strings.Split(env[catalogue.RuntimeToolModules], ",") {
+		if strings.HasPrefix(entry, module+"=") {
+			return true
+		}
+	}
+	return false
+}