feat(battle-node): OutboundSequencer assigns playSeq + archives for Resume

SVSim.BattleNode/Reliability/OutboundSequencer.cs

@@ -0,0 +1,27 @@
+using SVSim.BattleNode.Protocol;
+
+namespace SVSim.BattleNode.Reliability;
+
+/// <summary>
+/// Per-session outbound ledger. Assigns monotonic playSeq to ordered pushes and archives
+/// them for future Resume retransmit (v2). No-stock control pushes (BattleFinish/JudgeResult/Resume)
+/// are wrapped with no playSeq and skip the archive.
+/// </summary>
+public sealed class OutboundSequencer
+{
+    private long _next = 1;
+    private readonly Dictionary<long, MsgEnvelope> _archive = new();
+
+    public IReadOnlyDictionary<long, MsgEnvelope> Archive => _archive;
+
+    public MsgEnvelope AssignAndArchive(MsgEnvelope envelope)
+    {
+        var seq = _next++;
+        var stamped = envelope with { PlaySeq = seq };
+        _archive[seq] = stamped;
+        return stamped;
+    }
+
+    public MsgEnvelope WrapNoStock(MsgEnvelope envelope) =>
+        envelope with { PlaySeq = null };
+}