docs(rng-seam): note stableRandomCount divergence in HeadlessBattleMgr

SVSim.BattleEngine/Rng/HeadlessBattleMgr.cs

@@ -23,6 +23,11 @@ namespace SVSim.BattleEngine.Rng
             _rng = rng ?? new SeededRandomSource(contentsCreator.RandomSeed);
         }
 
+        // KNOWN DIVERGENCE: the base StableRandom/StableRandomDouble also bump a private
+        // `stableRandomCount` diagnostic field; these overrides cannot (it's private to the base) and do
+        // not. The field is currently unread anywhere in the engine, so this is harmless; if a future
+        // replay/audit path starts reading the count, promote it via a protected accessor (another DP5
+        // patch) rather than leaving it silently zero.
         public override int StableRandom(int val)
         {
             double unit = _rng.NextUnit();