Refuse enemies joining an open talk circle.

RankInvitees already skipped enemies when a circle formed; a later Chat in the same node still joined without checking opinions.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/HSchool.Simulation.Tests/TalkCircleTests.cs

@@ -52,6 +52,44 @@ public class TalkCircleTests
         }
     }
 
+    [Fact]
+    public void Enemy_StartsNeighborCircle_InsteadOfJoiningFriends()
+    {
+        var (school, pupils) = FivePupilsOnBreak();
+        using (school)
+        {
+            var first = pupils[0];
+            var second = pupils[1];
+            var enemy = pupils[2];
+            var ally = pupils[3];
+            OpinionStore.Set(first, second.Id, 55);
+            OpinionStore.Set(second, first.Id, 55);
+            OpinionStore.Set(enemy, first.Id, -55);
+            OpinionStore.Set(first, enemy.Id, -55);
+            OpinionStore.Set(enemy, second.Id, -55);
+            OpinionStore.Set(second, enemy.Id, -55);
+            OpinionStore.Set(enemy, ally.Id, 55);
+            OpinionStore.Set(ally, enemy.Id, 55);
+
+            PlaceAt(school, first.Id, "corridor-1");
+            PlaceAt(school, second.Id, "corridor-1");
+            Assert.True(school.TryStartAction(first.Id, TalkActions.Chat));
+            var friends = school.TalkCircleOf(first.Id);
+            Assert.NotNull(friends);
+            Assert.DoesNotContain(enemy.Id, friends.MemberIds);
+
+            PlaceAt(school, enemy.Id, "corridor-1");
+            PlaceAt(school, ally.Id, "corridor-1");
+            Assert.True(school.TryStartAction(enemy.Id, TalkActions.Chat));
+            var neighbor = school.TalkCircleOf(enemy.Id);
+            Assert.NotNull(neighbor);
+            Assert.NotEqual(friends.MemberIds, neighbor.MemberIds);
+            Assert.Contains(ally.Id, neighbor.MemberIds);
+            Assert.DoesNotContain(first.Id, neighbor.MemberIds);
+            Assert.Equal(friends.MemberIds, school.TalkCircleOf(first.Id)?.MemberIds);
+        }
+    }
+
     [Fact]
     public void FifthPerson_DoesNotJoinFullCircle()
     {