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

Defined in: [src/types/messages.ts:811](https://github.com/strands-agents/harness-sdk/blob/f23d6cce5a8fae509dc0ad28ee20de4be886e7d9/strands-ts/src/types/messages.ts#L811)