Add item registry extraction and validation

internal/modules/dnd/extract/itemregistry/schema_test.go

@@ -0,0 +1,25 @@
+package itemregistry
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+func TestItemResponseSchemaIsPrivateAndStructural(t *testing.T) {
+	schema, err := loadResponseSchema()
+	if err != nil {
+		t.Fatalf("loadResponseSchema() error = %v", err)
+	}
+	if schema.Key != ResponseSchemaKey || schema.ID != ResponseSchemaID || schema.Name != ResponseSchemaName || schema.Version != SchemaVersion || !strings.HasPrefix(schema.SHA256, "sha256:") || !json.Valid(schema.JSONSchema) {
+		t.Fatalf("schema = %#v, want item response schema", schema)
+	}
+	var document map[string]any
+	if err := json.Unmarshal(schema.JSONSchema, &document); err != nil {
+		t.Fatal(err)
+	}
+	encoded, err := json.Marshal(document)
+	if err != nil || strings.Contains(string(encoded), `"id"`) || !strings.Contains(string(encoded), `"additionalProperties":false`) {
+		t.Fatalf("schema = %s, want strict private response without durable ID", encoded)
+	}
+}