Function extractToolSequence

core/llm/countTokens.ts:228–280

* Extracts and validates the tool call sequence from the end of a message array. * Tool sequences consist of: [assistant_with_tool_calls, tool_response_1, tool_response_2, ...] * or just a single user message. * * @param messages - Array of chat messages (will be modified by popping messages) *

(messages: ChatMessage[])

 * @returns Array of messages that form the tool sequence
 */
function extractToolSequence(messages: ChatMessage[]): ChatMessage[] {
  const lastMsg = messages.pop();
  if (!lastMsg) {
    throw new Error("Error parsing chat history: no user/tool message found");
  }

  const toolSequence: ChatMessage[] = [];

  if (lastMsg.role === "tool") {
    toolSequence.push(lastMsg);

    // Collect all consecutive tool messages from the end
    while (
      messages.length > 0 &&
      messages[messages.length - 1].role === "tool"
    ) {
      toolSequence.unshift(messages.pop()!);
    }

    // Get the assistant message with tool calls
    const assistantMsg = messages.pop();
    if (assistantMsg) {
      toolSequence.unshift(assistantMsg);

      // Validate that all tool messages have matching tool call IDs
      for (const toolMsg of toolSequence.slice(1)) {
        // Skip assistant message
        if (
          toolMsg.role === "tool" &&
          !messageHasToolCallId(assistantMsg, toolMsg.toolCallId)
        ) {
          throw new Error(
            `Error parsing chat history: no tool call found to match tool output for id "${toolMsg.toolCallId}"`,
          );
        }
      }
    }
  } else if (lastMsg.role === "assistant" || lastMsg.role === "thinking") {
    toolSequence.push(lastMsg);
    while (
      messages.length > 0 &&
      (messages[messages.length - 1].role === "thinking" ||
        messages[messages.length - 1].role === "assistant")
    ) {
      toolSequence.unshift(messages.pop()!);
    }
  } else {
    // Single user message
    toolSequence.push(lastMsg);
  }

  return toolSequence;
}

function pruneLinesFromTop(
  prompt: string,