_prepare_responses_params() passed non-system messages straight through
as the Responses API "input" array without converting them. That's
fine for plain user/assistant text (matches the API's lenient "easy
input message" shape), but Chat-Completions-style assistant messages
carrying "tool_calls" and "tool"-role messages have no equivalent
shape in the Responses API - it expects standalone "function_call" and
"function_call_output" input items instead. Sending the raw
Chat-Completions shapes gets rejected with a 400 (union-type
validation failure against every Responses API input item variant).
This broke every multi-turn tool-calling conversation over
api="responses" that doesn't rely on auto_chain/previous_response_id
(i.e. the common case: resending full history each turn instead of
referencing server-side state).
Added _convert_message_to_responses_input_items() to translate:
- assistant + tool_calls -> one function_call item per call
- tool role -> function_call_output item
- everything else -> passed through unchanged
Verified against a real multi-turn tool-calling run: the agent now
completes the full conversation and returns the actual extracted
answer instead of erroring on the second turn.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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