refactor(battlenode): key dispatch on OpponentIsAckOnly, drop per-frame BattleType switch

Behavior-identical; 231 BattleNode tests green with ZERO test changes.

The 10 handler arms no longer switch on BattleType:
- 4 Bot arms gate on the new FrameDispatchContext.OpponentIsAckOnly
  (Other is not IHasHandshakePhase) — the participant property the audit asked for.
- 6 relay arms drop the Type == Pvp guard; it was redundant with BothSidesAfterReady()
  (only a two-real-player session has both handshake phases). Its doc now records that.
- FrameDispatchContext.Type removed (+ the Type = Type in BuildContext). BattleSession.Type
  stays for the session-level drop cascade.

Zero test churn because the stubs already encode the split: FakeRealParticipant/ProbeParticipant
implement IHasHandshakePhase, the bot stub FakeParticipant doesn't, and NewBotSession uses it as
the opponent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

SVSim.BattleNode/Sessions/BattleSession.cs

@@ -71,7 +71,7 @@ public sealed class BattleSession
         new()
         {
             A = A, B = B, From = from, Other = ReferenceEquals(from, A) ? B : A,
-            Env = env, Type = Type, BattleId = BattleId, State = _state,
+            Env = env, BattleId = BattleId, State = _state,
         };
 
     public BattleSession(string battleId, BattleType type, IBattleParticipant a, IBattleParticipant b,

SVSim.BattleNode/Sessions/Dispatch/FrameDispatchContext.cs

@@ -14,10 +14,17 @@ internal sealed class FrameDispatchContext
     internal required IBattleParticipant From { get; init; }
     internal required IBattleParticipant Other { get; init; }
     internal required MsgEnvelope Env { get; init; }
-    internal required BattleType Type { get; init; }
     internal required string BattleId { get; init; }
     internal required BattleSessionState State { get; init; }
 
+    /// <summary>The opponent is an AI-passive (ack-only) bot: it runs no handshake — no
+    /// <see cref="IHasHandshakePhase"/> — and receives no relayed frames (the client drives its own
+    /// AI; the server only acks). This is the participant property that replaces the per-handler
+    /// <c>BattleType.Bot</c> switch: the Bot dispatch arms gate on it. Its inverse — a live relay
+    /// peer — is what <see cref="BothSidesAfterReady"/> already implies (only real peers have a
+    /// handshake phase), so the relay arms need no separate opponent check.</summary>
+    internal bool OpponentIsAckOnly => Other is not IHasHandshakePhase;
+
     /// <summary>The dispatching participant's handshake phase (null for a non-IHasHandshakePhase
     /// participant, e.g. NoOpBot). Setting it advances the sender.</summary>
     internal HandshakePhase? SenderPhase
@@ -34,7 +41,10 @@ internal sealed class FrameDispatchContext
 
     /// <summary>BOTH participants have finished the handshake. Reads A/B (not From/Other) so the
     /// result is identical regardless of which side sent the frame. Contrast
-    /// <see cref="SenderIsAfterReady"/> (sender only).</summary>
+    /// <see cref="SenderIsAfterReady"/> (sender only). Only a live relay peer (real player) has a
+    /// handshake phase, so this can only be true in a two-real-player (PvP) session — the relay
+    /// dispatch arms gate on this instead of a <c>BattleType</c> check (an ack-only bot opponent,
+    /// <see cref="OpponentIsAckOnly"/>, can never satisfy it).</summary>
     internal bool BothSidesAfterReady() =>
         (A as IHasHandshakePhase)?.Phase == HandshakePhase.AfterReady &&
         (B as IHasHandshakePhase)?.Phase == HandshakePhase.AfterReady;

SVSim.BattleNode/Sessions/Dispatch/Handlers/EchoHandler.cs

@@ -13,7 +13,7 @@ internal sealed class EchoHandler : IFrameHandler
 {
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
-        if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+        if (ctx.BothSidesAfterReady())
         {
             var orderList = (ctx.Env.Body as RawBody)?.Entries.GetValueOrDefault(WireKeys.OrderList);
             ctx.State.RecordTokensFrom(ctx.From, ctx.Other, orderList);

SVSim.BattleNode/Sessions/Dispatch/Handlers/InitBattleHandler.cs

@@ -8,7 +8,7 @@ internal sealed class InitBattleHandler : IFrameHandler
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
         // case 2: Bot — ack only, NO Matched (Matched would corrupt client opponent info).
-        if (ctx.Type == BattleType.Bot && ctx.SenderPhase == HandshakePhase.AwaitingInitBattle)
+        if (ctx.OpponentIsAckOnly && ctx.SenderPhase == HandshakePhase.AwaitingInitBattle)
         {
             var r = new List<DispatchRoute>
             {

SVSim.BattleNode/Sessions/Dispatch/Handlers/JudgeHandler.cs

@@ -15,7 +15,7 @@ internal sealed class JudgeHandler : IFrameHandler
         // start another one, stalling the loop; confirmed by the 2026-06-03 two-client capture).
         // The sender then emits TurnStart, which TurnStartHandler relays to the opponent as {spin}.
         // battleCode is dropped; spin=0 for the deterministic-turn slice.
-        if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+        if (ctx.BothSidesAfterReady())
         {
             var frame = ctx.Env with { Body = new JudgeBody(Spin: BattleFrameDefaults.DeterministicTurnSpin) };
             return new[] { new DispatchRoute(ctx.From, frame, Stock.Normal) };

SVSim.BattleNode/Sessions/Dispatch/Handlers/LoadedHandler.cs

@@ -8,7 +8,7 @@ internal sealed class LoadedHandler : IFrameHandler
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
         // case 3: Bot — silent (client populates opponent state from AIBattleStart HTTP data).
-        if (ctx.Type == BattleType.Bot && ctx.SenderPhase == HandshakePhase.AwaitingLoaded)
+        if (ctx.OpponentIsAckOnly && ctx.SenderPhase == HandshakePhase.AwaitingLoaded)
         {
             ctx.SenderPhase = HandshakePhase.AwaitingSwap;
             return Array.Empty<DispatchRoute>();

SVSim.BattleNode/Sessions/Dispatch/Handlers/PlayActionsHandler.cs

@@ -14,7 +14,7 @@ internal sealed class PlayActionsHandler : IFrameHandler
 {
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
-        if (ctx.Type != BattleType.Pvp || !ctx.BothSidesAfterReady())
+        if (!ctx.BothSidesAfterReady())
             return Array.Empty<DispatchRoute>();
 
         var entries = (ctx.Env.Body as RawBody)?.Entries ?? new Dictionary<string, object?>();

SVSim.BattleNode/Sessions/Dispatch/Handlers/TurnEndActionsHandler.cs

@@ -9,7 +9,7 @@ internal sealed class TurnEndActionsHandler : IFrameHandler
 {
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
-        if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+        if (ctx.BothSidesAfterReady())
         {
             var frame = ctx.Env with { Body = new RawBody(new Dictionary<string, object?>()) };
             return new[] { new DispatchRoute(ctx.Other, frame, Stock.Normal) };

SVSim.BattleNode/Sessions/Dispatch/Handlers/TurnEndFinalHandler.cs

@@ -7,7 +7,7 @@ internal sealed class TurnEndFinalHandler : IFrameHandler
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
         // case 4: Bot — Judge to sender only.
-        if (ctx.Type == BattleType.Bot && ctx.SenderIsAfterReady)
+        if (ctx.OpponentIsAckOnly && ctx.SenderIsAfterReady)
             return new[] { new DispatchRoute(ctx.From, BattleFrames.BuildJudgeBroadcast(), Stock.Normal) };
 
         // case 9: general — forward the envelope to other + paired BattleFinish + Terminal.

SVSim.BattleNode/Sessions/Dispatch/Handlers/TurnEndHandler.cs

@@ -8,14 +8,14 @@ internal sealed class TurnEndHandler : IFrameHandler
     public IReadOnlyList<DispatchRoute> Handle(FrameDispatchContext ctx)
     {
         // case 4: Bot — Judge to sender only (no real opponent; client flips back to its local AI).
-        if (ctx.Type == BattleType.Bot && ctx.SenderIsAfterReady)
+        if (ctx.OpponentIsAckOnly && ctx.SenderIsAfterReady)
             return new[] { new DispatchRoute(ctx.From, BattleFrames.BuildJudgeBroadcast(), Stock.Normal) };
 
         // case 8: general AfterReady arm — PvP forwards a {turnState} TurnEnd to the opponent
         // (handover gate). Any non-Pvp non-Bot type that reaches AfterReady consumes the frame.
         if (ctx.SenderIsAfterReady)
         {
-            if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+            if (ctx.BothSidesAfterReady())
             {
                 // Opponent sees {turnState}; receiving TurnEnd drives ITS SendJudge (handover gate):
                 // the opponent (the turn taker-over) then sends a Judge, which JudgeHandler reflects

SVSim.BattleNode/Sessions/Dispatch/Handlers/TurnStartHandler.cs

@@ -10,7 +10,7 @@ internal sealed class TurnStartHandler : IFrameHandler
     {
         // PvP: the active player's TurnStart{orderList} is dropped; the opponent receives {spin}
         // (spin=0 for the deterministic-turn slice) and self-generates its turn-open.
-        if (ctx.Type == BattleType.Pvp && ctx.BothSidesAfterReady())
+        if (ctx.BothSidesAfterReady())
         {
             var frame = ctx.Env with { Body = new OpponentTurnStartBody(Spin: BattleFrameDefaults.DeterministicTurnSpin) };
             return new[] { new DispatchRoute(ctx.Other, frame, Stock.Normal) };