- add RetryWithBackoff helper to grpc client for exponential retry with backoff and reconnection-aware handling
- increase reconnectionClientTimeout to 90s and introduce connectionStabilizationDelay; wait briefly after reconnection to avoid immediate flapping
- refresh reconnection flag while waiting for client registration and improve cancellation message
- replace direct heartbeat RPC with RetryWithBackoff in WorkerService (use extended timeout)
- use RetryWithBackoff for worker node status updates in task handler and propagate errors
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