feat: queue messages + replace AI SDK with GraphQL SSE subscription (#19203)

## Summary

- **Queue messages while streaming**: Messages sent during active AI
streaming are queued server-side and auto-flushed when the current
stream completes. Frontend renders queued messages optimistically in a
dedicated queue UI.
- **Drop `@ai-sdk/react` + `resumable-stream`**: Replace the dual HTTP
SSE + AI SDK client architecture with a single GraphQL SSE subscription
per thread. All events (token chunks, message persistence, queue
updates, errors) flow through Redis PubSub → GraphQL subscription.
- **Server-driven architecture**: The server decides whether to queue or
stream (via `POST /:threadId/message`). The frontend mirrors this
decision for optimistic rendering but defers to the server response.
- **Reuse AI SDK accumulation logic**: `readUIMessageStream` from the
`ai` package handles chunk-to-message accumulation on the frontend,
avoiding a custom 780-line accumulator.

## Key files

**Backend:**
- `agent-chat-event-publisher.service.ts` — publishes events to Redis
PubSub
- `agent-chat-subscription.resolver.ts` — GraphQL subscription resolver
- `stream-agent-chat.job.ts` — publishes chunks via PubSub instead of
resumable-stream
- `agent-chat.controller.ts` — unified `POST /:threadId/message`
endpoint

**Frontend:**
- `useAgentChatSubscription.ts` — subscribes to `onAgentChatEvent`,
bridges to `readUIMessageStream`
- `useAgentChat.ts` — send/stop/optimistic rendering (no more AI SDK)
- `AgentChatStreamSubscriptionEffect.tsx` — replaces
`AgentChatAiSdkStreamEffect.tsx`

## Test plan

- [ ] Send message on new thread → optimistic render, streaming response
appears
- [ ] Send message while streaming → queued instantly (no flash in main
thread)
- [ ] Queued message auto-flushes after current stream completes
- [ ] Remove queued message via queue UI
- [ ] Stop streaming mid-response
- [ ] Leave chat idle for several minutes → streaming still works after
(SSE client recycling)
- [ ] Token refresh during session → requests succeed (authenticated
fetch)
- [ ] Switch threads while streaming → clean subscription handoff


Made with [Cursor](https://cursor.com)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/twenty-server/src/engine/subscriptions/subscriptions.module.ts

@@ -18,6 +18,7 @@ import { MetadataEventPublisher } from 'src/engine/subscriptions/metadata-event/
 import { MetadataEventsToDbListener } from 'src/engine/subscriptions/metadata-event/metadata-events-to-db.listener';
 import { ObjectRecordEventPublisher } from 'src/engine/subscriptions/object-record-event/object-record-event-publisher';
 import { SubscriptionService } from 'src/engine/subscriptions/subscription.service';
+import { WorkspaceEventBroadcaster } from 'src/engine/subscriptions/workspace-event-broadcaster/workspace-event-broadcaster.service';
 import { WorkspaceCacheModule } from 'src/engine/workspace-cache/workspace-cache.module';
 
 @Global()
@@ -40,6 +41,7 @@ import { WorkspaceCacheModule } from 'src/engine/workspace-cache/workspace-cache
     MetadataEventPublisher,
     MetadataEventEmitter,
     MetadataEventsToDbListener,
+    WorkspaceEventBroadcaster,
     ProcessNestedRelationsHelper,
     ProcessNestedRelationsV2Helper,
     CommonSelectFieldsHelper,
@@ -48,6 +50,7 @@ import { WorkspaceCacheModule } from 'src/engine/workspace-cache/workspace-cache
     SubscriptionService,
     ObjectRecordEventPublisher,
     MetadataEventEmitter,
+    WorkspaceEventBroadcaster,
   ],
 })
 export class SubscriptionsModule {}