- Add sync.Once to prevent double close of stopCh in Stop()
- Add nil fallback guard in NewStickySession (defaults to RoundRobin)
- Add atomic.Bool to make Start() idempotent
- Add tests for double Stop() and nil fallback scenarios
- Fix Select to check if cookie is expired before routing
- Add TestStickySession_ExpiredCookie test
- Expired cookies now trigger fallback + new cookie set
- Encode cookie as base64(target_url + | + timestamp) per spec
- Use cookie value (not targetURL) for shard key and session map keys
- Add missing sticky.Start() calls in tests
- Fix time precision in cookie encode/decode tests