Function logStepTiming

packages/agent-core/src/loop/turn-step.ts:236–257

* Emit a per-step completion log with the LLM response timing. TTFT is split * into the client-side request-build portion and the network + API-server * portion, and the decode window is split into server (awaiting parts) vs. * client (processing parts) time, so slow turns can be attributed witho

(
  log: Logger | undefined,
  turnId: string,
  step: number,
  response: LLMChatResponse,
)

 * parsing the wire log.
 */
function logStepTiming(
  log: Logger | undefined,
  turnId: string,
  step: number,
  response: LLMChatResponse,
): void {
  if (log === undefined) return;
  const timing = response.streamTiming;
  if (timing === undefined) return;
  log.info('llm response', {
    turnStep: `${turnId}/${String(step)}`,
    ttftMs: timing.firstTokenLatencyMs,
    ...(timing.requestBuildMs !== undefined ? { requestBuildMs: timing.requestBuildMs } : {}),
    ...(timing.serverFirstTokenMs !== undefined
      ? { serverFirstTokenMs: timing.serverFirstTokenMs }
      : {}),
    streamDurationMs: timing.streamDurationMs,
    ...(timing.serverDecodeMs !== undefined ? { serverDecodeMs: timing.serverDecodeMs } : {}),
    ...(timing.clientConsumeMs !== undefined ? { clientConsumeMs: timing.clientConsumeMs } : {}),
    outputTokens: response.usage.output,
  });
}

function deriveStepStopReason(response: LLMChatResponse): LoopStepStopReason {
  switch (response.providerFinishReason) {