Processing failures recorded during the turn.
The stage's parsed output, or null when the turn failed.
The provider response id for this turn (nullable for non-chaining
providers such as chat-completions). For a turn that failed it is the
last response the provider returned, which the stage may have
rejected, or null when none returned. A caller chaining turns should
keep its previous id when the turn failed (it recorded failures and
produced no output), as createConversation does.
Cumulative token usage for this turn's LLM call.
Result of a single conversational turn. Mirrors the shape the server's Argument Builder actions need: output, the new response id, token usage, and any processing failures.