Function trimConversationHistory

server/src/utils/token-limiter.ts:172–263

(
  messages: MessageTurn[],
  tokenLimit: number
)

 * @returns Trimmed messages and metadata
 */
export function trimConversationHistory(
  messages: MessageTurn[],
  tokenLimit: number
): TrimResult {
  if (messages.length === 0) {
    return {
      messages: [],
      estimatedTokens: 0,
      messagesRemoved: 0,
      wasTrimmed: false,
    };
  }

  const originalCount = messages.length;

  // Estimate tokens for each message, including tool call content
  const messagesWithTokens = messages.map(msg => {
    let tokens = estimateTokens(msg.content);
    if (msg.toolCalls) {
      for (const tc of msg.toolCalls) {
        tokens += estimateTokens(tc.name);
        tokens += estimateTokens(tc.result);
        if (tc.input) tokens += estimateTokens(JSON.stringify(tc.input));
      }
    }
    return { message: msg, tokens };
  });

  // Start from the end (most recent) and work backwards
  let totalTokens = 0;
  const includedMessages: MessageTurn[] = [];

  // Always try to include the most recent message (current user turn)
  // Work backwards from the end
  for (let i = messagesWithTokens.length - 1; i >= 0; i--) {
    const { message, tokens } = messagesWithTokens[i];

    if (totalTokens + tokens <= tokenLimit) {
      // Fits within limit - add to front (to maintain order)
      includedMessages.unshift(message);
      totalTokens += tokens;
    } else if (includedMessages.length === 0) {
      // Even the most recent message doesn't fit - truncate it
      const availableChars = Math.floor(tokenLimit * 3.5);
      const truncateAt = Math.max(0, availableChars - 100);
      const truncatedContent = message.content.substring(0, truncateAt) +
        '\n\n[Message truncated due to length]';

      logger.warn(
        {
          originalTokens: tokens,
          truncatedTo: estimateTokens(truncatedContent),
          tokenLimit,
        },
        'Token limiter: Truncated single message that exceeded limit'
      );

      includedMessages.unshift({