mode

When using mode="fork", configure the remote agent to match the parent's model, system prompt, tools, and prompt-processing middleware if you want prompt-cache reuse. Fork mode copies conversation history; it does not synchronize those settings. Matching configuration is necessary but not sufficient: the rendered prefix must match, and cache hits depend on the provider.

• isolated (default): send only the delegated task description.
• fork: send a snapshot of the parent's conversation at launch, followed by the task description, for background work.

Different configurations are supported for context sharing, but you should not expect parent-to-child cache reuse with them.