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server : merge contiguous Responses input items into a single assistant message #19773

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Merged
pwilkin merged 4 commits into from
Feb 22, 2026
Merged

server : merge contiguous Responses input items into a single assistant message #19773

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070b68d
server : merge contiguous input items into a single assistant message
aldehir Feb 21, 2026
38dc926
cont : simplify tool call msg
aldehir Feb 21, 2026
304a0e9
cont : reduce and combine content
aldehir Feb 21, 2026
3c4ff18
cont : fix merging content items
aldehir Feb 21, 2026
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81 changes: 42 additions & 39 deletions tools/server/server-common.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1104,6 +1104,11 @@ json convert_responses_to_chatcmpl(const json & response_body) {
return j.contains(key) && j.at(key).is_string();
};

// Return true if we should merge with the last message
auto should_merge = [&chatcmpl_messages]() -> bool {
return !chatcmpl_messages.empty() && chatcmpl_messages.back().value("role", "") == "assistant";
};

for (json item : input_value) {
if (exists_and_is_string(item, "content")) {
// #responses_create-input-input_item_list-input_message-content-text_input
Expand Down Expand Up @@ -1210,35 +1215,43 @@ json convert_responses_to_chatcmpl(const json & response_body) {
});
}

item.erase("status");
item.erase("type");
item["content"] = chatcmpl_content;
chatcmpl_messages.push_back(item);
if (should_merge()) {
auto & prev_msg = chatcmpl_messages.back();
prev_msg["content"] = chatcmpl_content;
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} else {
item.erase("status");
item.erase("type");
item["content"] = chatcmpl_content;
chatcmpl_messages.push_back(item);
}
} else if (exists_and_is_string(item, "arguments") &&
exists_and_is_string(item, "call_id") &&
exists_and_is_string(item, "name") &&
exists_and_is_string(item, "type") &&
item.at("type") == "function_call"
) {
// #responses_create-input-input_item_list-item-function_tool_call
json msg = json {
{"role", "assistant"},
{"tool_calls", json::array({ json {
{"function", json {
{"arguments", item.at("arguments")},
{"name", item.at("name")},
}},
{"id", item.at("call_id")},
{"type", "function"},
}})},
json tool_call = {
{"function", json {
{"arguments", item.at("arguments")},
{"name", item.at("name")},
}},
{"id", item.at("call_id")},
{"type", "function"},
};

if (!chatcmpl_messages.empty() && chatcmpl_messages.back().contains("reasoning_content")) {
// Move reasoning content from dummy message to tool call message
msg["reasoning_content"] = chatcmpl_messages.back().at("reasoning_content");
chatcmpl_messages.pop_back();
if (should_merge()) {
auto & prev_msg = chatcmpl_messages.back();
if (!exists_and_is_array(prev_msg, "tool_calls")) {
prev_msg["tool_calls"] = json::array();
}
prev_msg["tool_calls"].push_back(tool_call);
} else {
chatcmpl_messages.push_back(json {
{"role", "assistant"},
{"tool_calls", json::array({tool_call})}
});
}
chatcmpl_messages.push_back(msg);
} else if (exists_and_is_string(item, "call_id") &&
(exists_and_is_string(item, "output") || exists_and_is_array(item, "output")) &&
exists_and_is_string(item, "type") &&
Expand Down Expand Up @@ -1282,12 +1295,16 @@ json convert_responses_to_chatcmpl(const json & response_body) {
throw std::invalid_argument("item['content']['text'] is not a string");
}

// Pack reasoning content in dummy message
chatcmpl_messages.push_back(json {
{"role", "assistant"},
{"content", json::array()},
{"reasoning_content", item.at("content")[0].at("text")},
});
if (should_merge()) {
auto & prev_msg = chatcmpl_messages.back();
prev_msg["reasoning_content"] = item.at("content")[0].at("text");
} else {
chatcmpl_messages.push_back(json {
{"role", "assistant"},
{"content", json::array()},
{"reasoning_content", item.at("content")[0].at("text")},
});
}
} else {
throw std::invalid_argument("Cannot determine type of 'item'");
}
Expand All @@ -1296,20 +1313,6 @@ json convert_responses_to_chatcmpl(const json & response_body) {
throw std::invalid_argument("'input' must be a string or array of objects");
}

// Remove unused dummy message which contains
// reasoning content not followed by tool call
chatcmpl_messages.erase(std::remove_if(
chatcmpl_messages.begin(),
chatcmpl_messages.end(),
[](const json & x){ return x.contains("role") &&
x.at("role") == "assistant" &&
x.contains("content") &&
x.at("content") == json::array() &&
x.contains("reasoning_content");
}),
chatcmpl_messages.end()
);

chatcmpl_body["messages"] = chatcmpl_messages;

if (response_body.contains("tools")) {
Expand Down
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