agen integrates streaming LLM responses and tool execution in an agent engine. It manages turns, history appends, pause/resume, and retries, while the LLM client layer handles wire formats and authentication. The caller owns history storage, worker lifecycle control, and compaction.

Design entry points

[Engine]: turn execution, interruption, and resumption
[History]: model input paired with caller-owned annotations
[state] and [prune]: prefix protection and request-only history projections
[llm_client] and [timeline]: wire-format conversion and event processing
[interceptor]: host-owned control decisions