Function shouldAutoCompact

extensions/cli/src/compaction.ts:266–315

(params: AutoCompactParams)

 * @returns Whether auto-compacting should be triggered
 */
export function shouldAutoCompact(params: AutoCompactParams): boolean {
  const { chatHistory, model, systemMessage, tools } = params;

  const inputTokens = countTotalInputTokens({
    chatHistory,
    systemMessage,
    tools,
    model,
  });
  const contextLimit = getModelContextLimit(model);
  const maxTokens = getModelMaxTokens(model);

  // Additional buffer matching the auto-compaction threshold formula
  const ratioCompactionBuffer = Math.ceil(
    (1 - AUTO_COMPACT_BUFFER_RATIO) * (contextLimit - maxTokens),
  );
  const safeCompactionBuffer = Math.max(maxTokens, ratioCompactionBuffer);
  const compactionBuffer = Math.min(
    safeCompactionBuffer,
    AUTO_COMPACT_BUFFER_CAP,
  );

  const compactionThreshold = contextLimit - maxTokens - compactionBuffer;

  // Ensure we have positive space available for input
  if (compactionThreshold <= 0) {
    throw new Error(
      `max_tokens is larger than context_length, which should not be possible. Please check your configuration.`,
    );
  }

  const toolTokens = tools ? countToolDefinitionTokens(tools) : 0;
  const systemTokens = systemMessage ? encode(systemMessage).length : 0;
  const shouldCompact = inputTokens >= compactionThreshold;

  logger.debug("Context usage check", {
    inputTokens,
    historyTokens: countChatHistoryTokens(chatHistory, model),
    systemTokens,
    toolTokens,
    contextLimit,
    maxTokens,
    reservedForOutput: maxTokens,
    compactionBuffer,
    compactionThreshold,
    shouldCompact,
  });

  return shouldCompact;
}