Install command batches through one path

registry_test.go

@@ -56,8 +56,8 @@ func TestAppsHaveIndependentRegistries(t *testing.T) {
 	if _, exists := second.commands["custom"]; exists {
 		t.Fatal("registration leaked to another app")
 	}
-	if !first.commands["help"].reserved || !first.commands["version"].reserved {
-		t.Fatal("New did not reserve generated root commands")
+	if first.commands["help"] == nil || first.commands["help"].command.record.payload == nil || first.commands["version"] == nil || first.commands["version"].command.record.payload == nil {
+		t.Fatal("New did not install real help and version declarations")
 	}
 }
 
@@ -138,6 +138,55 @@ func TestRootGroupRetainsPlacementMetadata(t *testing.T) {
 	}
 }
 
+func TestBatchInstallationRejectsNestedRootOnlyAndKeepsExistingState(t *testing.T) {
+	root := RootGroup("config", "Configuration.")
+	app, err := New(Identity{Name: "Example"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := app.Register(Group("outer", "", root)); err == nil {
+		t.Fatal("installation accepted nested root-only declaration")
+	}
+	if _, exists := app.commands["outer"]; exists {
+		t.Fatal("failed batch partially installed its parent")
+	}
+	if err := app.Register(root); err != nil {
+		t.Fatalf("root-level declaration rejected: %v", err)
+	}
+}
+
+func TestNoOpOnlyRegistrationPreservesRoutingSnapshot(t *testing.T) {
+	app, err := New(Identity{Name: "Example"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	before := app.bridgeTree()
+	if err := app.Register(NoCommand()); err != nil {
+		t.Fatal(err)
+	}
+	if after := app.bridgeTree(); after != before {
+		t.Fatal("no-op-only registration invalidated derived metadata")
+	}
+}
+
+func TestCapturedDeclarationCanBeInstalledIntoMultipleApps(t *testing.T) {
+	declaration := Group("tools", "", NewCommand(CommandSpec[struct{}]{Name: "run"}))
+	first, err := New(Identity{Name: "First"}, declaration)
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := New(Identity{Name: "Second"}, declaration)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := first.commandAt([]string{"tools", "run"}); !ok {
+		t.Fatal("first app lost reused declaration")
+	}
+	if _, ok := second.commandAt([]string{"tools", "run"}); !ok {
+		t.Fatal("second app lost reused declaration")
+	}
+}
+
 func TestWithErrorCopiesDeclarationAndRetainsWrappedCauses(t *testing.T) {
 	first := errors.New("first construction issue")
 	second := errors.New("second construction issue")