delete-fences.ts:7:1 - error SC1090: 'delete' of hybrid index-signature keys (declared struct slots and overflow entries answer differently — model deletable dynamic keys with a pure Record<string, T>) are not supported yet

  6 | const h: Hybrid = { base: "b", extra: "e" };
  7 | delete h["extra"];
    | ^~~~~~~~~~~~~~~~~
  8 | console.log(h.base);