feat: stubs s3_upload, s3_download, s3_presign_url (issue 0014 fase 4)

functions/infra/s3_presign_url.go

@@ -0,0 +1,17 @@
+package infra
+
+import (
+	"fmt"
+	"time"
+)
+
+// S3PresignURL genera una URL presignada para download (GET) del objeto key,
+// valida durante expiry.
+//
+// STUB: la implementacion real requiere github.com/aws/aws-sdk-go-v2 (s3.PresignClient).
+func S3PresignURL(cfg S3Config, key string, expiry time.Duration) (string, error) {
+	_ = cfg
+	_ = key
+	_ = expiry
+	return "", fmt.Errorf("s3_presign_url: not implemented (requiere github.com/aws/aws-sdk-go-v2)")
+}