Add reference contracts to extractor metadata

internal/framework/pipeline/module_test.go

@@ -0,0 +1,25 @@
+package pipeline
+
+import (
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
+)
+
+func TestValidateModuleSpecRejectsReferenceSlotsForNonExtractors(t *testing.T) {
+	err := validateModuleSpec("chunker", StageChunk, ModuleSpec{
+		Key:   "generic",
+		Stage: StageChunk,
+		ReferenceSlots: []contracts.ReferenceSlot{
+			{Name: "roster"},
+		},
+	})
+
+	if err == nil {
+		t.Fatal("validateModuleSpec() error = nil, want error")
+	}
+	if !strings.Contains(err.Error(), "reference slots") {
+		t.Fatalf("validateModuleSpec() error = %q, want reference slots context", err.Error())
+	}
+}