# Flow F3 — Real-time SSE Subscription

Cross-reference: `system-flows.md` → Flow F3.

## Sequence

```mermaid
sequenceDiagram
    autonumber
    participant UI
    participant Ctrl as AnnotationsController.Events (component 02 doc-ownership)
    participant Evt as AnnotationEventService (02)
    participant ProducerF1 as Flow F1 (annotation create)
    participant ProducerF8 as Flow F8 (dataset bulk status)

    UI->>Ctrl: GET /annotations/events (Accept: text/event-stream, JWT ANN)
    Ctrl->>Ctrl: set Content-Type: text/event-stream, no-cache
    Ctrl->>Evt: ReadAllAsync(cancellationToken)
    par event sources
        ProducerF1->>Evt: PublishAsync(eventDto)
        ProducerF8->>Evt: PublishAsync(eventDto)
    end
    Evt-->>Ctrl: yield AnnotationEventDto
    Ctrl-->>UI: data: {json}\n\n
    UI--xCtrl: client disconnects
    Ctrl->>Ctrl: cancellation token fires; loop exits
```

## State

```mermaid
stateDiagram-v2
    [*] --> Subscribing
    Subscribing --> Streaming: header sent + reader attached
    Streaming --> Streaming: PublishAsync -> data frame
    Streaming --> Closed: client cancel / process restart
    Closed --> [*]
```

## Notes

- Channel is **unbounded**: a slow client cannot back-pressure the producer. If a client stalls indefinitely, memory growth is bounded by per-publisher cancellation tokens at the controller level. Step 4 verification candidate.
- Cross-pod fan-out is **not provided** — each pod has its own channel. Sticky sessions or a broker-backed bus required for horizontal scale.