## Problem
There is a race condition in the chat stream reconnect path. When a
client connects (or reconnects) to `/stream`, sometimes they only see a
`status: running` event but never receive any `message_part` events —
the stream appears stuck.
## Root Cause
In `processChat`, the sequence is:
1. `publishStatus(running)` — broadcasts `status: running` to all
subscribers and via pubsub.
2. `runChat()` is called.
3. Inside `runChat`, there's significant setup work (model resolution,
DB queries, title generation, prompt building, instruction resolution).
4. Only **after** all that setup does `runChat` set `buffering = true`
on the stream state.
If a client connects to `/stream` between steps 1 and 4:
- `Subscribe()` reads `chat.Status == running` from the DB, so it
includes `status: running` in the snapshot.
- But `buffering` is still `false`, so `subscribeToStream` returns an
**empty** local snapshot (no message_parts).
- `publishToStream` **drops** all `message_part` events when `buffering`
is false.
- Result: client sees `running` but never gets any streaming content.
## Fix
Move the `buffering = true` setup (and its deferred cleanup) from
`runChat` into `processChat`, right before `publishStatus(running)`.
This guarantees the buffer is active before any subscriber can observe
`status: running`, so:
- The snapshot always includes any in-flight `message_part` events.
- `publishToStream` never drops parts because buffering is already on.
Kyle Carberry
5b1cf4a6a3