QueryEngine previously guarded stream_event yields behind includePartialMessages,
which was undefined in serve mode. Remove the guard so stream_event messages
always flow to the child process stdout. Add stream_event handling in
sessionHandle.routeMessage to emit via EventBus for downstream consumers.
- Add _providerId field to SessionHandle, extracted from initData.account.apiProvider
- Include provider_id in user message emit, assistant message fallback, and session.ready
- Revert getProviderId normalization (keep raw value from subprocess)
- Remove process.stderr.write debug logs from sessionHandle and prompt_async
- Add model fallback in assistant message (use this._model if msg.model missing)
- Add model field to user message emit for adapter consumption
- Wait for session ready before setModel/prompt in prompt_async
- Return 200 JSON instead of 204 No Content from prompt_async
- Set Bun.serve idleTimeout to 255s to prevent connection drops
