refactor(battle-node): gate WS diagnostic logging behind config flag

The temporary [sio-in] / [sio-out] / [ws-rx-text] / [ws-rx-bin] /
[ws-recv-exit] / [ws-loop-exit] logs added during the hand-ack
investigation are useful enough to keep around (PvP testing, future WS
debugging) but too chatty to leave on by default. Promote them from
"strip before merge" to a permanent opt-in.

New BattleNodeOptions.DiagnosticLogging (bool, default false). Wired
through BattleNodeWebSocketHandler to RealParticipant via a new optional
ctor parameter (default false — existing test sites pick up the silent
default with no changes). Every Information/Warning log added during the
investigation is now if-gated; non-diagnostic logs (the decode-failure
warnings, the dispatch-drop debug) stay as-is.

Toggle via appsettings*.json:
  "BattleNode": { "DiagnosticLogging": true }

Or live via the singleton:
  factory.Services.GetRequiredService<BattleNodeOptions>().DiagnosticLogging = true

175 battle-node tests still passing — existing tests use the constructor
default and emit nothing, so no test changes were required.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleNode/Bridge/BattleNodeOptions.cs

@@ -26,4 +26,18 @@ public sealed class BattleNodeOptions
     /// is the only way to get PvP behavior.</para>
     /// </summary>
     public bool SoloDefaultsToScripted { get; set; } = false;
+
+    /// <summary>
+    /// When true, <see cref="Sessions.Participants.RealParticipant"/> emits per-frame
+    /// diagnostic logs at Information level: <c>[sio-in]</c> on every inbound msg/alive/hand
+    /// envelope (URI, pubSeq, ackId, dispatch decision, ack-sent flag, ack arg, inbound
+    /// watermark); <c>[sio-out]</c> on every outbound push (URI, pubSeq, playSeq, noStock);
+    /// <c>[ws-rx-text]</c> / <c>[ws-rx-bin]</c> on every WS frame received at the transport
+    /// layer; <c>[ws-recv-exit]</c> / <c>[ws-loop-exit]</c> on read-loop termination
+    /// (with WebSocket state + exception type when applicable). Default false — keeps
+    /// production logs clean. Flip on per session for live WS debugging, PvP investigation,
+    /// or to reproduce the kind of softlock chased in
+    /// <c>docs/audits/battle-node-sio-events-2026-06-02.md</c>.
+    /// </summary>
+    public bool DiagnosticLogging { get; set; } = false;
 }

SVSim.BattleNode/Hosting/BattleNodeWebSocketHandler.cs

@@ -124,7 +124,7 @@ public sealed class BattleNodeWebSocketHandler
             {
                 _store.RemovePending(battleId);
                 var realParticipant = new RealParticipant(ws, viewerId, pending.P1.Context,
-                    _loggerFactory.CreateLogger<RealParticipant>());
+                    _loggerFactory.CreateLogger<RealParticipant>(), _options.DiagnosticLogging);
                 var scriptedBot = new ScriptedBotParticipant();
                 var session = new BattleSession(battleId, pending.Type, realParticipant, scriptedBot,
                     _loggerFactory.CreateLogger<BattleSession>());
@@ -137,7 +137,7 @@ public sealed class BattleNodeWebSocketHandler
                 // Pick this connection's MatchContext (P1's if isP1, P2's if isP2).
                 var selfCtx = isP1 ? pending.P1.Context : pending.P2!.Context;
                 var self = new RealParticipant(ws, viewerId, selfCtx,
-                    _loggerFactory.CreateLogger<RealParticipant>());
+                    _loggerFactory.CreateLogger<RealParticipant>(), _options.DiagnosticLogging);
 
                 var firstArriver = _waitingRoom.Pair(battleId, self);
 
@@ -202,7 +202,7 @@ public sealed class BattleNodeWebSocketHandler
                 // earlier isP1/isP2 check has already rejected viewer mismatches.
                 _store.RemovePending(battleId);
                 var botReal = new RealParticipant(ws, viewerId, pending.P1.Context,
-                    _loggerFactory.CreateLogger<RealParticipant>());
+                    _loggerFactory.CreateLogger<RealParticipant>(), _options.DiagnosticLogging);
                 var noopBot = new NoOpBotParticipant();
                 var botSession = new BattleSession(battleId, BattleType.Bot, botReal, noopBot,
                     _loggerFactory.CreateLogger<BattleSession>());

SVSim.BattleNode/Sessions/Participants/RealParticipant.cs

@@ -33,6 +33,7 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
 {
     private readonly WebSocket _ws;
     private readonly ILogger<RealParticipant> _log;
+    private readonly bool _diagnosticLogging;
     private CancellationToken _sessionCt;
 
     public long ViewerId { get; }
@@ -85,10 +86,11 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
     }
 
     public RealParticipant(WebSocket ws, long viewerId, MatchContext context,
-        ILogger<RealParticipant> log)
+        ILogger<RealParticipant> log, bool diagnosticLogging = false)
     {
         _ws = ws;
         _log = log;
+        _diagnosticLogging = diagnosticLogging;
         ViewerId = viewerId;
         Context = context;
     }
@@ -115,11 +117,13 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
                     var text = Encoding.UTF8.GetString(msg.Value.Bytes);
                     if (text.Length == 0) continue;
                     var eio = EngineIoFrame.Parse(text);
-                    // Diagnostic: log every EIO frame type so we can see Ping/Close packets too.
+                    if (_diagnosticLogging)
-                    _log.LogInformation(
+                    {
-                        "[ws-rx-text] viewer={Vid} eioType={Eio} len={Len} preview={Preview}",
+                        _log.LogInformation(
-                        ViewerId, eio.Type, text.Length,
+                            "[ws-rx-text] viewer={Vid} eioType={Eio} len={Len} preview={Preview}",
-                        text.Length > 60 ? text.Substring(0, 60) + "..." : text);
+                            ViewerId, eio.Type, text.Length,
+                            text.Length > 60 ? text.Substring(0, 60) + "..." : text);
+                    }
                     if (eio.Type == EngineIoPacketType.Ping)
                     {
                         await SendTextAsync("3", cancellation);
@@ -144,9 +148,12 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
                         bin = bin.AsSpan(1).ToArray();
                     }
                     pendingAttachments.Add(bin);
-                    _log.LogInformation(
+                    if (_diagnosticLogging)
-                        "[ws-rx-bin] viewer={Vid} binLen={Len} pendingFrame={Pending} attachCount={AttachCount}",
+                    {
-                        ViewerId, bin.Length, pendingFrame?.EventName ?? "(null)", pendingAttachments.Count);
+                        _log.LogInformation(
+                            "[ws-rx-bin] viewer={Vid} binLen={Len} pendingFrame={Pending} attachCount={AttachCount}",
+                            ViewerId, bin.Length, pendingFrame?.EventName ?? "(null)", pendingAttachments.Count);
+                    }
                     if (pendingFrame is not null && pendingAttachments.Count == pendingFrame.AttachmentCount)
                     {
                         var assembled = pendingFrame.WithAttachments(pendingAttachments.ToArray());
@@ -163,20 +170,24 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
         }
         finally
         {
-            _log.LogWarning(
+            if (_diagnosticLogging)
-                "[ws-loop-exit] viewer={Vid} reason={Reason} wsState={State} cancelled={Cancelled}",
+            {
-                ViewerId, exitReason, _ws.State, cancellation.IsCancellationRequested);
+                _log.LogWarning(
+                    "[ws-loop-exit] viewer={Vid} reason={Reason} wsState={State} cancelled={Cancelled}",
+                    ViewerId, exitReason, _ws.State, cancellation.IsCancellationRequested);
+            }
         }
     }
 
     public async Task PushAsync(MsgEnvelope envelope, bool noStock, CancellationToken ct)
     {
         var stamped = noStock ? Outbound.WrapNoStock(envelope) : Outbound.AssignAndArchive(envelope);
-        // Temporary diagnostic log to pair with the [sio-in] log — gives full inbound/outbound
+        if (_diagnosticLogging)
-        // sequence numbering for the scripted-attack TurnEnd-never-fires investigation.
+        {
-        _log.LogInformation(
+            _log.LogInformation(
-            "[sio-out] viewer={Vid} uri={Uri} pubSeq={Pseq} playSeq={Plseq} noStock={NoStock}",
+                "[sio-out] viewer={Vid} uri={Uri} pubSeq={Pseq} playSeq={Plseq} noStock={NoStock}",
-            ViewerId, stamped.Uri, stamped.PubSeq, stamped.PlaySeq, noStock);
+                ViewerId, stamped.Uri, stamped.PubSeq, stamped.PlaySeq, noStock);
+        }
         await EncodeAndSendAsync(stamped, WireConstants.SynchronizeEvent, ct);
     }
 
@@ -241,21 +252,12 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
                     ackArg = env.PubSeq.Value;
                 }
             }
-            // Temporary diagnostic log to chase a scripted-bot bug where the client
+            if (_diagnosticLogging)
-            // sends TurnEndActions after a PlayActions(type=10) attack but never sends the
+            {
-            // follow-up TurnEnd. We need to confirm whether the server actually sent the
+                _log.LogInformation(
-            // SIO ack for the offending TurnEndActions (and what arg). Log shape:
+                    "[sio-in] viewer={Vid} uri={Uri} pubSeq={Pseq} ackId={AckId} dispatch={Dispatch} ackSent={AckSent} ackArg={AckArg} highWaterMark={Hwm}",
-            //   uri / pubSeq / ackId / dispatch / ackSent / ackArg / watermark
+                    ViewerId, env.Uri, env.PubSeq, frame.AckId, shouldDispatch, ackSent, ackArg, Inbound.HighWaterMark);
-            _log.LogInformation(
+            }
-                "[sio-in] viewer={Vid} uri={Uri} pubSeq={Pseq} ackId={AckId} dispatch={Dispatch} ackSent={AckSent} ackArg={AckArg} highWaterMark={Hwm}",
-                ViewerId,
-                env.Uri,
-                env.PubSeq,
-                frame.AckId,
-                shouldDispatch,
-                ackSent,
-                ackArg,
-                Inbound.HighWaterMark);
 
             if (!shouldDispatch) return;
 
@@ -409,19 +411,22 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
             try { result = await _ws.ReceiveAsync(buffer, ct); }
             catch (OperationCanceledException)
             {
-                _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=OperationCanceled wsState={State}", ViewerId, _ws.State);
+                if (_diagnosticLogging)
+                    _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=OperationCanceled wsState={State}", ViewerId, _ws.State);
                 return null;
             }
             catch (WebSocketException wsex)
             {
-                _log.LogWarning(wsex, "[ws-recv-exit] viewer={Vid} reason=WebSocketException wsState={State} errCode={ErrCode}",
+                if (_diagnosticLogging)
-                    ViewerId, _ws.State, wsex.WebSocketErrorCode);
+                    _log.LogWarning(wsex, "[ws-recv-exit] viewer={Vid} reason=WebSocketException wsState={State} errCode={ErrCode}",
+                        ViewerId, _ws.State, wsex.WebSocketErrorCode);
                 return null;
             }
             if (result.MessageType == WebSocketMessageType.Close)
             {
-                _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=ClientCloseFrame wsState={State} closeStatus={Status} desc={Desc}",
+                if (_diagnosticLogging)
-                    ViewerId, _ws.State, result.CloseStatus, result.CloseStatusDescription);
+                    _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=ClientCloseFrame wsState={State} closeStatus={Status} desc={Desc}",
+                        ViewerId, _ws.State, result.CloseStatus, result.CloseStatusDescription);
                 return null;
             }
             ms.Write(buffer, 0, result.Count);