test(battle-engine M13): shared NetworkEmitFixtureBase teardown — close IsForecast/agent global leak

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

SVSim.BattleEngine.Tests/NetworkEmitFixtureBase.cs

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+using NUnit.Framework;
+
+namespace SVSim.BattleEngine.Tests
+{
+    // Shared base for every network-emit test fixture (M13 EmitPathReadOracleTests, the
+    // construction-probe's OnEmit seam test, and any M14+ network fixture to come).
+    //
+    // WHY this exists — the global-state leak it closes:
+    //   HeadlessEngineEnv.NewNetworkEmitBattle() mutates two PROCESS globals that no per-mgr
+    //   teardown reverts on its own:
+    //     - Wizard.ToolboxGame.RealTimeNetworkAgent: a non-null agent is injected so the engine's
+    //       NetworkBattleSender ToolboxGame.RealTimeNetworkAgent.* calls resolve (the capture seam).
+    //     - BattleManagerBase.IsForecast: the emit path needs this FALSE, so the harness flips it from
+    //       the EnsureInitialized default of TRUE.
+    //   HeadlessEngineEnv.EnsureInitialized() is _done-guarded — it sets IsForecast=true exactly once
+    //   and then NO-OPs forever after. So once a network-emit fixture leaves IsForecast=false behind,
+    //   nothing restores it: a later SOLO fixture (e.g. RandomDrawOracleTests) that assumes
+    //   IsForecast=true would silently run with IsForecast=false (un-suppressed VFX) and a stale
+    //   injected agent. Currently latent-benign, but a real hygiene gap M14's added network fixtures
+    //   could turn flaky.
+    //
+    // Deriving from this base means NUnit runs the base-class [TearDown] after EVERY test in the
+    // derived fixture automatically, so the reset can never be forgotten when a new network-emit
+    // fixture is added — inherit this, don't re-roll a local teardown.
+    public abstract class NetworkEmitFixtureBase
+    {
+        [TearDown]
+        public void ResetNetworkEmitGlobals()
+        {
+            // Clear the injected agent (the solo oracles don't read it, but clearing it is defensive,
+            // mirroring RandomDrawOracleTests.ResetRandomDrawGate).
+            Wizard.ToolboxGame.SetRealTimeNetworkBattle(null);
+            // Restore the EnsureInitialized default. This is the load-bearing restore: every solo
+            // oracle and EnsureInitialized assume IsForecast=TRUE, and EnsureInitialized only sets it
+            // once (guarded), so without restoring it here a solo fixture running after a network-emit
+            // fixture would see IsForecast=false and un-suppressed VFX.
+            BattleManagerBase.IsForecast = true;
+        }
+    }
+}