v2.9.0

Fixed

• The polling fallback no longer ends the SSE stream. After max_stream_retries (5) consecutive failures — about 31 seconds of unreachability, so an edge incident, a bad deploy or a network partition — the streaming thread called on_give_up and exited, and the core cleared its handler, so nothing could ever restart streaming: the process lost real-time updates until it was restarted (or Featureflip.restart was called by hand for fork-safety) and polled /v1/sdk/flags every 30 seconds indefinitely. Flag changes, kill switches included, then arrived up to a poll interval late. Polling is now additive — it covers the outage while the stream keeps retrying underneath at the capped, jittered backoff, and the next delivered frame retires the poller. The poller is retired from the frame-delivery path rather than when the stream next drops, because a healthy stream blocks in its read loop for its whole lifetime and a poller left running beside it reverts SSE deltas with its own whole-store replaces. (#3071)