Stream Resumption

FluxyChat stream resumption lets users reconnect to in-progress AI responses after a page refresh, network drop, or tab switch without losing partial output.

The Problem

When an AI agent streams a long response (e.g., a detailed code review), and the user refreshes the page or briefly loses connectivity, the stream breaks. Without resumption:

• The partial response is lost
• The user must re-trigger the agent
• Tokens already generated are wasted

How It Works

1. Stream start: When an AI stream begins, the worker assigns it a streamId and persists chunks to D1 as they arrive
2. Disconnection: The WebSocket drops; the stream continues server-side
3. Reconnection: The client reconnects and requests stream resume with the streamId
4. Resume: The worker replays buffered chunks, then switches to live streaming for remaining content
5. Completion: Stream finalizes normally; the full message is persisted

SDK Usage

import { useChat } from "@fluxy-chat/sdk";

const { messages, resumeStream } = useChat({ roomId, client });

// On reconnect, the SDK automatically attempts to resume active streams
// You can also manually trigger resume:
await resumeStream(streamId);

Manual Stream Resume

// After reconnecting, check for active streams
const activeStreams = await client.getActiveStreams(roomId);

for (const stream of activeStreams) {
  await client.resumeStream(stream.id);
}

WebSocket Events

During stream resumption, the following events flow over WebSocket:

Worker Configuration

Stream resumption is enabled by default. Configure via environment variables:

STREAM_RESUMPTION_ENABLED=true          # default: true
STREAM_RESUMPTION_TTL_SECONDS=300        # how long to keep stream state (default: 5 min)
STREAM_RESUMPTION_MAX_CONCURRENT=10      # max concurrent resumable streams per room

Integration with Existing Features

• SSE fallback: Stream resumption works across transport fallbacks (WS → SSE → polling)
• Agent runtime: The agent-runtime.js module checks for resumable streams on agent start
• Room DO: The Durable Object tracks activeStreams and sends streamState on WebSocket reconnect
• DevTools: The DevTools UI shows active streams and their resume status

See Also

• LLM Middleware Guide — Intercept and modify stream behavior
• Workflow Agent Guide — Durable agent execution that survives restarts