fix(operations): stabilize empty policy audit

vehicle-data-platform/apps/api/internal/platform/source_policy_store.go

@@ -32,7 +32,7 @@ ORDER BY protocol, source_key`, vin)
 }
 
 func (s *ProductionStore) VehicleSourcePolicy(ctx context.Context, vin string) (VehicleSourcePolicyConfig, error) {
-	config := VehicleSourcePolicyConfig{VIN: vin, Version: 1, UpdatedBy: "system"}
+	config := VehicleSourcePolicyConfig{VIN: vin, Version: 1, UpdatedBy: "system", Audit: []VehicleSourcePolicyAudit{}}
 	var updatedAt sql.NullString
 	err := s.db.QueryRowContext(ctx, `SELECT version, updated_by,
 DATE_FORMAT(updated_at, '%Y-%m-%d %H:%i:%s')

vehicle-data-platform/apps/api/internal/platform/source_policy_test.go

@@ -0,0 +1,43 @@
+package platform
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+)
+
+func TestProductionVehicleSourcePolicyUsesStableEmptyAuditArray(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	store := NewProductionStore(db, nil, "")
+	mock.ExpectQuery(`SELECT version, updated_by`).WithArgs("VIN001").
+		WillReturnRows(sqlmock.NewRows([]string{"version", "updated_by", "updated_at"}))
+	mock.ExpectQuery(`SELECT version, protocol, source_ref`).WithArgs("VIN001").
+		WillReturnRows(sqlmock.NewRows([]string{"version", "protocol", "source_ref", "source_label", "actor", "changed_at", "summary"}))
+	config, err := store.VehicleSourcePolicy(context.Background(), "VIN001")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if config.Audit == nil || len(config.Audit) != 0 {
+		t.Fatalf("empty audit must be a stable slice: %#v", config.Audit)
+	}
+	encoded, err := json.Marshal(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(encoded) == "" || !json.Valid(encoded) {
+		t.Fatalf("policy JSON is invalid: %s", encoded)
+	}
+	if !bytes.Contains(encoded, []byte(`"audit":[]`)) {
+		t.Fatalf("empty audit encoded as null: %s", encoded)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatal(err)
+	}
+}