docs(battle-engine M13): note _notEmit precondition on TryReadStockedEmitData (review polish)

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

SVSim.BattleEngine.Tests/HeadlessFixture.cs

@@ -440,6 +440,9 @@ namespace SVSim.BattleEngine.Tests
         // expected to be null/empty — return null on any null/throw so the test degrades to Inconclusive
         // rather than failing. Field `stockEmitMessageMgr` (:103) + `GetSequenceAllData()`
         // (StockEmitMgr.cs:81, returns List<Dictionary<string,object>>) verified against the copied engine.
+        // Precondition: this is expected-null ONLY while NewNetworkEmitBattle sets _notEmit=true and leaves
+        // stockEmitMessageMgr unconstructed. If that harness setup changes, revisit — a non-null stock should
+        // then make the test ASSERT on the payload rather than defer to Inconclusive.
         public static System.Collections.IList TryReadStockedEmitData(RealTimeNetworkAgent agent)
         {
             try