sequenceDiagram
    participant O as Orchestrator
    participant P as pipeline.Process
    participant PR as processRequest
    participant S as stream()
    participant G as firstEventTimeoutGuard
    participant E as Executor.DoStream
    participant N as nextLlmStreamEvent

    O->>P: Process(ctx, request)
    P->>PR: processRequest(ctx, llmRequest)

    alt Streaming request
        PR->>S: stream(ctx, executor, req, streamFirstEventTimeout)
        S->>G: newFirstEventTimeoutGuard(ctx, timeout)
        G-->>S: streamCtx, guard
        S->>E: DoStream(streamCtx, req)
        E-->>S: outboundStream
        Note over G: timer fires, CAS pending to timedOut, cancel(streamCtx)
        S->>N: "nextLlmStreamEvent(ctx, llmStream, firstEvent=true, guard)"
        N->>N: llmStream.Next() blocked until streamCtx cancelled or event arrives
        alt Event arrives first
            N->>G: acceptFirstEvent() CAS pending to completed, stop timer
            N-->>S: (true, nil)
        else Timeout fires first
            N->>G: "completeFirstEventPhase() CAS fails state=timedOut"
            N->>G: timedOut() returns true
            N-->>S: (false, ErrStreamFirstEventTimeout)
        end
        S-->>PR: stream or ErrStreamFirstEventTimeout
    else Non-streaming request
        PR->>PR: withNonStreamTimeout(ctx) returns timeoutCtx
        PR->>PR: notStream or autoAggregateStream with timeoutCtx
        Note over PR: context.WithTimeoutCause sets cause=ErrNonStreamResponseTimeout on expiry
        PR->>PR: isNonStreamTimeout(timeoutCtx) via context.Cause
        PR-->>P: response or ErrNonStreamResponseTimeout
    end

    alt isResponseTimeoutError(lastErr)
        P->>P: skip same-channel retry
        P->>P: NextChannel() channel switch
    else Normal error
        P->>P: CanRetry() same-channel retry first
        P->>P: NextChannel() if same-channel exhausted
    end
    P->>P: time.Sleep(retryDelay) applied to all retries including timeout