engine cleanup passes 4-7 + multi-instancing ambient rip

Squashes 146 commits from battle-engine-extraction. Net: 2,045 files changed,
+11,896 / -158,687 lines. Ships engine passes 4-7 (dead-code cull, view-layer
stub, receive-path shrink) plus the Phase-5 AsyncLocal ambient deletion that
turns concurrent battles into a type-system property rather than a scope
contract.

## What landed

**Passes 4-7 (chunks 1-34):** Extended the Phase-4 const-false collapse into a
cascading cull across the skill graph, view layer, and receive-path periphery.
Six mode flags (IsWatchBattle/IsReplayBattle/IsAdmin/IsAdminWatch/IsPuzzleQuest/
IsAINetwork) became `const false`, every guarded block deleted. Field*.cs
subclass ctors + BackGroundBase + ObjectChecker culled to no-ops. Mulligan
family reworked to take a mgr param through IMulliganMgr.InitMulligan.
Emotion/Recovery/Resource clusters null-stubbed. Prediction/OperationSimulator/
skill filters converted from static ambient reads to per-mgr reads via
SkillPrm.ownerCard.SelfBattlePlayer.BattleMgr / ins.BattleMgr / this.BattleMgr.

**Phase-5 ambient rip (chunks 35-47):** Deleted BattleAmbient / BattleAmbient-
Context / TestBattleScope in full. Every per-battle mutable slot now lives on
the mgr instance itself:
  mgr.InstanceIsForecast / InstanceIsRandomDraw / InstanceRecoveryInfo /
  InstanceViewerId / InstanceNetworkAgent / GameMgr
BattleManagerBase.GetIns() returns null unconditionally; the residual static
flags + 3 façades (Certification.ViewerId, Data.BattleRecoveryInfo,
ToolboxGame.RealTimeNetworkAgent) are null-tolerant defaults kept for the
handful of engine-internal readers that still reference their types. Zero
BattleAmbient references anywhere in engine + node + tests.

Added pre-seeded GameMgr ctor overload threaded through the mgr chain
(BattleManagerBase → SingleBattleMgr / NetworkBattleManagerBase → NetworkStandard-
BattleMgr → HeadlessBattleMgr / HeadlessNetworkBattleMgr). Fixtures build a
GameMgr, seed it via HeadlessEngineEnv.SeedCharaIds/SeedNetUser, and pass it
to the mgr's ctor — no ambient reach.

Node side (SVSim.BattleNode/SessionBattleEngine): _ctx replaced with a plain
GameMgr field; 34 `using var _ambient = BattleAmbient.Enter(_ctx)` scope wraps
ripped from every accessor and mutator; EngineGlobalInit.WirePerSessionGameMgr
takes GameMgr as a param and runs from SessionBattleEngine.SetupInternal
BEFORE mgr construction.

Test side: TestBattleScope deleted; 18 fixture [SetUp]s migrated to
`HeadlessEngineEnv.EnsureProcessGlobals()`; MultiInstanceEngineTests rewritten
around per-mgr construction (GetIns() → null is the pinned invariant).

## Regression fixes

- **chunk-48** (MulliganCtrl): chunk-35's `= null` stubs on card lookups broke
  the live receive-driven Deal path (BattlePlayerBase.DrawCard NRE'd downstream
  of NetworkPlayerMulliganCtrl.StartMulliganVfx). Restored the three lookups
  via `_battlePlayer.BattleMgr.GetBattleCardIdx`. Engine tests were satisfied
  by the WireMulliganPhase seam; unit tests exposed the live-path gap.

## Ship state

- SVSim.BattleEngine.Tests: 56/56 pass, 2 skip
- SVSim.UnitTests: 1554/1554 pass (was 1523/31-fail before chunk 48)
- Solution build: 0 source warnings (40 pre-existing NU1902 MessagePack CVEs
  in SVSim.EmulatedEntrypoint, unrelated)
- Sequential PVP smoke: verified live (two back-to-back battles, no regression
  on cleanup/spinup)
- Concurrent PVP smoke: verified live

Adds tools/engine-port/ClosureAnalyzer/ — the Roslyn transitive-type-closure
analyzer needed to make future cascade cleanup safe (per feedback memory
"Engine cleanup needs closure tool" from the 2026-06-28 pass-3 failure).

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

SVSim.BattleNode/Sessions/Participants/RealParticipant.cs

@@ -204,9 +204,23 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
         {
             if (_diagnosticLogging)
             {
-                _log.LogWarning(
-                    "[ws-loop-exit] viewer={Vid} reason={Reason} wsState={State} cancelled={Cancelled}",
-                    ViewerId, exitReason, _ws.State, cancellation.IsCancellationRequested);
+                // Clean-teardown terminators (normal client close, or a null read after
+                // cancellation was requested) log at Info; anything else stays Warn so
+                // genuine crashes stay visible even with diagnostics on.
+                bool cleanExit = exitReason == "read-returned-null" &&
+                    (cancellation.IsCancellationRequested || _ws.State is WebSocketState.CloseReceived or WebSocketState.Closed);
+                if (cleanExit)
+                {
+                    _log.LogInformation(
+                        "[ws-loop-exit] viewer={Vid} reason={Reason} wsState={State} cancelled={Cancelled}",
+                        ViewerId, exitReason, _ws.State, cancellation.IsCancellationRequested);
+                }
+                else
+                {
+                    _log.LogWarning(
+                        "[ws-loop-exit] viewer={Vid} reason={Reason} wsState={State} cancelled={Cancelled}",
+                        ViewerId, exitReason, _ws.State, cancellation.IsCancellationRequested);
+                }
             }
         }
     }
@@ -495,7 +509,14 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
             catch (OperationCanceledException)
             {
                 if (_diagnosticLogging)
-                    _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=OperationCanceled wsState={State}", ViewerId, _ws.State);
+                {
+                    // A cancellation-requested cancel is a normal session teardown; a spontaneous
+                    // OperationCanceled without cancellation being requested is a real anomaly.
+                    if (ct.IsCancellationRequested)
+                        _log.LogInformation("[ws-recv-exit] viewer={Vid} reason=OperationCanceled wsState={State}", ViewerId, _ws.State);
+                    else
+                        _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=OperationCanceled wsState={State}", ViewerId, _ws.State);
+                }
                 return null;
             }
             catch (WebSocketException wsex)
@@ -508,8 +529,15 @@ public sealed class RealParticipant : IBattleParticipant, IHasHandshakePhase
             if (result.MessageType == WebSocketMessageType.Close)
             {
                 if (_diagnosticLogging)
-                    _log.LogWarning("[ws-recv-exit] viewer={Vid} reason=ClientCloseFrame wsState={State} closeStatus={Status} desc={Desc}",
-                        ViewerId, _ws.State, result.CloseStatus, result.CloseStatusDescription);
+                {
+                    // NormalClosure ("Bye!") at battle-end is expected; abnormal close statuses stay Warn.
+                    if (result.CloseStatus == WebSocketCloseStatus.NormalClosure)
+                        _log.LogInformation("[ws-recv-exit] viewer={Vid} reason=ClientCloseFrame wsState={State} closeStatus={Status} desc={Desc}",
+                            ViewerId, _ws.State, result.CloseStatus, result.CloseStatusDescription);
+                    else
+                        _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);