fix(exports): stabilize published types and compatibility with updated dependencies

ts/skr.invoice.storage.ts

@@ -224,7 +224,8 @@ export class InvoiceStorage {
       return contentHash;
     } catch (error) {
       this.logger.log('error', `Failed to store invoice: ${error}`);
-      throw new Error(`Invoice storage failed: ${error.message}`);
+      const errorMessage = error instanceof Error ? error.message : String(error);
+      throw new Error(`Invoice storage failed: ${errorMessage}`);
     }
   }
   
@@ -707,4 +708,4 @@ export class InvoiceStorage {
     
     this.logger.log('info', `Updated metadata for invoice: ${contentHash}`);
   }
-}
+}