Translate the request into LangGraph input.
Default implementation builds a {"messages": [...]} payload from
exactly one conversation-state source:
responses_history mode prepends conversation history resolved
from previous_response_id / conversation via the configured
:class:ResponseProviderProtocol.langgraph_checkpoint mode passes only the current request input;
prior state is restored by LangGraph through thread_id.Override in a subclass to support custom-state graphs.
The parsed create-response request.
The response context for the request.
function_call_output items whose
call_id is in this set are excluded from the messages
payload. Populated by the HITL resume path so the resume
item isn't double-fed to the graph.