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## 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>