```ts
type SystemContentBlock =
  | TextBlock
  | CachePointBlock
  | GuardContentBlock;
```

Defined in: [src/types/messages.ts:813](https://github.com/strands-agents/harness-sdk/blob/4b38b7443afa906bd2b3be1a7d7ce0cb44f39684/strands-ts/src/types/messages.ts#L813)