[Copilot]

Adds a reliability layer on top of existing UDP client/server with sequencing, ACKs, retransmission, and duplicate detection.

Protocol

• 9-byte header: [1B flags][4B sequence][4B ack] prepended to payload
• DATA flag triggers ACK response; ACK flag clears pending retransmission
• Monotonically increasing sequence numbers for duplicate/ordering detection
• Thread-safe receive sequence updates via Interlocked.CompareExchange

Core library (source/NetCoreServer/)

• RudpClient — extends UdpClient, adds SendReliable/SendReliableAsync with all standard overloads
• RudpServer — extends UdpServer, per-endpoint state tracking via ConcurrentDictionary
• Internal ACK handling is transparent; ACK-only packets auto-continue the receive loop
• OnReliableReceived delivers stripped payload; OnRetransmissionFailure signals exhausted retries

Settings (properties, matching existing conventions)

• OptionRetransmissionTimeout — ms before retransmit (default: 1000)
• OptionMaxRetransmissions — max retry count (default: 5)
• OptionWindowSize — max unacked in-flight packets (default: 64)

Usage

// Server
class MyServer : RudpServer
{
    public MyServer(IPAddress addr, int port) : base(addr, port) {}
    protected override void OnStarted() => ReceiveAsync();
    protected override void OnReliableReceived(EndPoint ep, byte[] buf, long off, long sz)
        => SendReliable(ep, buf, off, sz); // echo
    protected override void OnSent(EndPoint ep, long sent)
        => ThreadPool.QueueUserWorkItem(_ => ReceiveAsync());
}

// Client
client.SendReliable("hello"); // sequenced, acked, retransmitted if needed

Tests, examples, perf

• tests/RudpTests.cs — echo test, multi-message test, settings validation
• examples/RudpEchoServer + RudpEchoClient — interactive examples
• performance/RudpEchoServer + RudpEchoClient — benchmarking harness with throughput/latency reporting
• All projects added to solution file

Original prompt

Add reliable UDP implementation (RUDP) for existing UDP implementation.
remember about examples, tests, perf, ...
If there can be some settings for a server, make them like they are in existing code by properties.

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