Support for store.has syscall

plug-api/plugos-syscall/store.ts

@@ -31,6 +31,10 @@ export function get(key: string): Promise<any> {
   return syscall("store.get", key);
 }
 
+export function has(key: string): Promise<boolean> {
+  return syscall("store.has", key);
+}
+
 export function del(key: string): Promise<void> {
   return syscall("store.delete", key);
 }