Initialize narratio Go module and CLI scaffold

internal/artifacts/local.go

@@ -0,0 +1,31 @@
+package artifacts
+
+import (
+	"context"
+	"fmt"
+)
+
+// LocalStore is a placeholder local filesystem artifact store.
+type LocalStore struct {
+	RootDir string
+}
+
+// WriteLocal returns a not-yet-implemented error in the scaffold.
+func (s *LocalStore) WriteLocal(_ context.Context, _ Ref, _ []byte) error {
+	return fmt.Errorf("artifacts local write: not yet implemented")
+}
+
+// ReadLocal returns a not-yet-implemented error in the scaffold.
+func (s *LocalStore) ReadLocal(_ context.Context, _ Ref) ([]byte, error) {
+	return nil, fmt.Errorf("artifacts local read: not yet implemented")
+}
+
+// ExistsLocal returns a not-yet-implemented error in the scaffold.
+func (s *LocalStore) ExistsLocal(_ context.Context, _ Ref) (bool, error) {
+	return false, fmt.Errorf("artifacts local exists: not yet implemented")
+}
+
+// Upload returns a not-yet-implemented error in the scaffold.
+func (s *LocalStore) Upload(_ context.Context, _ Ref) (string, error) {
+	return "", fmt.Errorf("artifacts local upload: not yet implemented")
+}