Function finalContextTokensFromLastResponse

src/utils/tokens.ts:79–112

(
  messages: Message[],
)

 * Both paths exclude cache tokens to match #304930's formula.
 */
export function finalContextTokensFromLastResponse(
  messages: Message[],
): number {
  let i = messages.length - 1
  while (i >= 0) {
    const message = messages[i]
    const usage = message ? getTokenUsage(message) : undefined
    if (usage) {
      // Stainless types don't include iterations yet — cast like advisor.ts:43
      const iterations = (
        usage as {
          iterations?: Array<{
            input_tokens: number
            output_tokens: number
          }> | null
        }
      ).iterations
      if (iterations && iterations.length > 0) {
        const last = iterations.at(-1)!
        return last.input_tokens + last.output_tokens
      }
      // No iterations → no server tool loop → top-level usage IS the final
      // window. Match the iterations path's formula (input + output, no cache)
      // rather than getTokenCountFromUsage — #304930 defines final window as
      // non-cache input + output. Whether the server's budget countdown
      // (renderer.py:292 calculate_context_tokens) counts cache the same way
      // is an open question; aligning with the iterations path keeps the two
      // branches consistent until that's resolved.
      return usage.input_tokens + usage.output_tokens
    }
    i--
  }
  return 0
}

/**
 * Get only the output_tokens from the last API response.