fix(stealth): hide concealed players from server ping

src/test/java/games/dmg/spigotstealth/ServerListPingVisibilityTest.java

@@ -0,0 +1,43 @@
+package games.dmg.spigotstealth;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import java.util.Set;
+import java.util.UUID;
+import org.junit.jupiter.api.Test;
+
+class ServerListPingVisibilityTest {
+    @Test
+    void publicPlayerCountNeverBecomesNegative() {
+        ServerListPingVisibility.Snapshot adjusted = ServerListPingVisibility.adjust(
+                0, 100, List.of(), Set.of(UUID.randomUUID()));
+
+        assertEquals(0, adjusted.playersOnline());
+    }
+
+    @Test
+    void ordinaryPlayersRemainCountedAndSampled() {
+        UUID firstId = UUID.randomUUID();
+        UUID secondId = UUID.randomUUID();
+
+        ServerListPingVisibility.Snapshot adjusted = ServerListPingVisibility.adjust(
+                2, 100, List.of(firstId, secondId), Set.of());
+
+        assertEquals(2, adjusted.playersOnline());
+        assertEquals(List.of(firstId, secondId), adjusted.samplePlayerIds());
+    }
+
+    @Test
+    void excludesConcealedPlayersFromPublicCountAndSampleWithoutChangingMaximum() {
+        UUID visibleId = UUID.randomUUID();
+        UUID concealedId = UUID.randomUUID();
+
+        ServerListPingVisibility.Snapshot adjusted = ServerListPingVisibility.adjust(
+                2, 100, List.of(visibleId, concealedId), Set.of(concealedId));
+
+        assertEquals(1, adjusted.playersOnline());
+        assertEquals(100, adjusted.playersMaximum());
+        assertEquals(List.of(visibleId), adjusted.samplePlayerIds());
+    }
+}

src/test/java/games/dmg/spigotstealth/StealthSessionServiceTest.java

@@ -1,15 +1,35 @@
 package games.dmg.spigotstealth;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.time.Duration;
 import java.time.Instant;
 import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 import org.junit.jupiter.api.Test;
 
 class StealthSessionServiceTest {
+    @Test
+    void reportsOnlyCurrentlyConcealedPlayerIdsForPublicPresentation() {
+        UUID concealedId = UUID.randomUUID();
+        UUID staleId = UUID.randomUUID();
+        try (StealthStateManager manager = manager()) {
+            manager.update(state -> state
+                    .withPlayer(unlocked(concealedId).withSession(true, false))
+                    .withPlayer(unlocked(staleId).withSession(false, true)))
+                    .join();
+            QualifyingInvisibilityService progression = new QualifyingInvisibilityService(
+                    manager, Duration.ofHours(8), System::nanoTime, ignored -> { });
+            StealthSessionService sessions = new StealthSessionService(manager, progression);
+            sessions.login(concealedId, "Hidden");
+
+            assertEquals(Set.of(concealedId), sessions.concealedPlayerIds());
+        }
+    }
+
     @Test
     void unlockedQualifyingDisconnectPreparesAndConsumesOneConcealedLogin() {
         UUID playerId = UUID.randomUUID();