ExperimentalOptionalcancelPermits the client to cancel this child's current work without ending
the session. Omitted or null means unsupported; an object (including
{}) means supported.
Optional_The _meta property is reserved by ACP to allow clients and agents to attach additional metadata to their interactions. Implementations MUST NOT make assumptions about values at these keys.
UNSTABLE
This capability is not part of the spec yet, and may be removed or changed at any point.
Client-initiated session mutations permitted for a specific subagent session.
A mutation requires an explicit per-child capability; support for the method on ordinary sessions does not grant support on a child.