- Add in-memory ModelConfigCache (30s refresh, explicit invalidation) replacing 2 SQLite queries per request (model lookup + cost override) - Configure all 5 provider HTTP clients with proper timeouts (300s), connection pooling (4 idle/host, 90s idle timeout), and TCP keepalive - Move client_usage update to tokio::spawn in non-streaming path - Use fast chars/4 heuristic for token estimation on large inputs (>1KB) - Generate single UUID/timestamp per SSE stream instead of per chunk - Add shared LazyLock<Client> for image fetching in multimodal module - Add proxy overhead timing instrumentation for both request paths - Fix test helper to include new model_config_cache field