This module contains the OpenChamber message-stream WebSocket protocol and runtime bridge. It keeps the browser-facing WebSocket transport separate from the upstream OpenCode SSE transport.
## Entrypoints and structure
-`packages/web/server/lib/event-stream/index.js`: public entrypoint re-exporting protocol and runtime helpers.
-`MESSAGE_STREAM_WS_HEARTBEAT_INTERVAL_MS`: heartbeat interval for browser-facing WS connections.
-`parseSseEventEnvelope(block)`: parses an SSE block into `{ eventId, directory, payload }`.
-`sendMessageStreamWsFrame(socket, payload)`: serializes and sends a JSON WS frame.
-`sendMessageStreamWsEvent(socket, payload, options)`: sends an event frame with optional `eventId` and `directory`.
### Runtime helpers
-`createGlobalUiEventBroadcaster({ sseClients, wsClients, writeSseEvent })`: returns a broadcaster that fans out the same synthetic UI event to SSE and WS clients.
-`createMessageStreamWsRuntime(...)`: mounts the message-stream WS server, upgrade handler, and SSE-to-WS bridge onto the web HTTP server.
## Runtime behavior
- Browser clients connect to the WS endpoints above.
- OpenChamber still fetches OpenCode upstream event streams over SSE.
- Each WS connection proxies one upstream SSE stream.
- If an upstream SSE stream stalls after the browser WS is already ready, the runtime aborts that upstream fetch and reconnects upstream with `Last-Event-ID`, keeping the browser WS alive when recovery is fast.
- Health checks are reserved for initial upstream connect failures and explicit upstream-unavailable responses, not for ordinary stall recovery on an already-established stream.
- Global synthetic events such as `openchamber:session-status`, `openchamber:session-activity`, `openchamber:notification`, and `openchamber:heartbeat` are preserved on the WS path, but heartbeat frames are emitted only while an upstream SSE stream is actively attached.
