Expand description
The default ReAct-style loop: thought → action → observation.
Emits only lifecycle events (meta, run.*, turn.*, budget.exceeded).
llm.* and tool.* events are produced by RequestTracer and
ToolTracer in oharness-trace, wired in by Agent::run
(see docs/remaining-work.md §2.4 — M1b-δ refactor).