CallerDetails interface

Caller details for scope creation. Supports human callers, agent callers, or both (A2A with a human in the chain).

Migration note: In v1 the name CallerDetails referred to human caller identity (now UserDetails). In v2 it was repurposed as a wrapper that groups both human and agent caller information.

See UserDetails — human caller identity (previously CallerDetails) See CHANGELOG.md — breaking changes section for migration guidance