step：调用、落盘与三条分支

380  private async step(decision: Extract<PreparedStep, { kind: 'enter' }>): Promise<StepEndReason | null> {
384    const { assembly } = decision
387    const renderedPrompt = renderPrompt(assembly)
388    let firstAttempt = true      // 0.1.5：首次尝试才注入 user/system 消息重试不再重复注入
389    while (true) {
390      const { config, preparedCall } = await this.prepareRequest(turn, step, signal)拆分 1：解析配置 + 绑定 adapter
391      const startsRequestSeries = firstAttempt && decision.startsRequestSeries === true
392      const commits = this.systemPrompt.project(renderedPrompt, {   // system prompt 投影取代 header.system 赋值
393        inHistory: preparedCall?.systemPromptUpdate === 'in-history',
394        startsSeries: startsRequestSeries
395          || this.requestSurfaceGeneration !== this.session.surface.replaceGeneration
396          || this.toolsChanged(assembly.tools),
397      })
398      for (const { message, intent } of commits) {
399        this.session.append('system/message', { turn, step, message }, intent)落盘为 surface 事件
400      }
401      if (firstAttempt) {
402        for (const message of decision.messages) {
403          this.session.append('user/message', message, { surfaceOp: 'append' })
404        }
405      }
406      firstAttempt = false
407      const request = this.buildRequest(config, preparedCall, assembly.tools, startsRequestSeries, signal)拆分 2：组装冻结请求
408      const live = new AssistantStreamAttempt(
409        this.session.id,
410        ++this.assistantAttemptCounter,
411        () => ++this.assistantStreamRevision,
412        turn, step,
414        (frame) => { this.dispatch.emit('agent/assistant-stream', { frame }) },
415      )
416      let started = false
417      try {
418        const stream = preparedCall?.stream(request) ?? this.loopCtx.llm.stream(request)
420        live.start()
421        started = true
422        for await (const chunk of stream) {
424          live.push(chunk)
425        }
427      } catch (error: unknown) {
428        if (!started) throw error
433              live.settle('assistant/message', () => this.session.append('assistant/message', {
451        throw error
452      }
453      try {
454        const finish = live.finish
455        if (finish.kind === 'error' || finish.kind === 'aborted') {
456          live.settle('assistant/attempt', () => this.session.append('assistant/attempt', {
457            turn, step, stream: live.stream,
458          }).seq)
460          const action = await this.dispatch.waterfall(
461            'agent/request-error', { turn, step, provider: request.provider,
462              failure: finish.failure, retryPolicy: preparedCall?.retryPolicy, signal },
469            () => Promise.resolve<RequestErrorAction>(undefined),
470          )
472          if (action?.kind !== 'retry') {
473            throw new LlmError(finish.failure.message, finish.failure.code, finish.failure)
474          }
475          continue
476        }
478        const message = createAssistantMessage({
479          content: live.blocks(),
480          source: { provider: request.provider, model: request.model,
483            ...live.replayState !== undefined ? { replayState: live.replayState } : {} },
484        })
486        live.settle('assistant/message', () => this.session.append('assistant/message', {
487          turn, step, message,
489          ...live.usage === undefined ? {} : { usage: live.usage },
490          stream: live.stream,
491        }, { surfaceOp: 'append' }).seq)
492        if (finish.kind === 'max-tokens') return { kind: 'max-tokens' }
494        const toolCalls = message.content.filter(block => block.type === 'tool-call')
495        if (toolCalls.length === 0) return { kind: 'completed' }
516        const { concluded } = await executeToolCalls(
517          this.loopCtx, turn, step, toolCalls, signal,
518          context => this.inbox.splice('next-step', this.inbox.nextStep.length, 0, [context]),
519        )
520        return concluded ? { kind: 'completed' } : null
522        if (!live.ended) live.abandon()
523        throw error
524      }
525    }
526  }