Phase 7: one End boss at a time; more visible attack telegraphs

Adrian (2026-11-02): a second Eternatus appeared on his second visit
to the End; the attacks should be more visible.

- EndBoss waits until the entities around its spot are loaded before
  deciding it's missing, refuses a second copy while the recorded one
  is alive (join check, like the guardians), and removes extra copies
  near the spot (cleans up worlds that already have two).
- Telegraphs: 2.2-size dust redrawn every 2 ticks, the inside filled
  (Area.fill), rising sparks on the outline, a low bell on cast.
- Tests: no second End boss (after the End's middle is loaded), fill
  points inside their areas.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

mod/src/main/kotlin/dev/cobblesurvival/selftest/BossTests.kt

@@ -71,7 +71,8 @@ object BossTests {
         s.check(line.contains(Vec3(8.0, 64.0, 0.5)) && !line.contains(Vec3(8.0, 64.0, 2.0)) && !line.contains(Vec3(-2.0, 64.0, 0.0))) { "line" }
         val cone = Area.Cone(o, Math.PI / 2, 10.0, Math.toRadians(30.0))  // along +z
         s.check(cone.contains(Vec3(2.0, 64.0, 8.0)) && !cone.contains(Vec3(8.0, 64.0, 2.0)) && !cone.contains(Vec3(0.0, 64.0, 11.0))) { "cone" }
-        s.check(listOf(circle, ring, line, cone).all { it.outline().isNotEmpty() }) { "a shape without telegraph points" }
+        s.check(listOf(circle, ring, line, cone).all { it.outline().isNotEmpty() && it.fill().isNotEmpty() }) { "a shape without telegraph points" }
+        s.check(listOf(circle, ring, line, cone).all { area -> area.fill().all { area.contains(it) } }) { "telegraph points outside their area" }
         s.helper.succeed()
     }
 
@@ -160,26 +161,35 @@ object BossTests {
 
     private fun endBoss(s: Scenario) {
         val end = s.level.server.getLevel(Level.END) ?: throw GameTestAssertException("no End")
-        val chunks = (-2..2).flatMap { x -> (-2..2).map { z -> ChunkPos(x, z) } }
+        val chunks = (-3..3).flatMap { x -> (-3..3).map { z -> ChunkPos(x, z) } }
         chunks.forEach { end.setChunkForced(it.x, it.z, true) }
         val player = s.player()
         s.afterTest {
             EndBoss.current(end)?.discard()
             chunks.forEach { end.setChunkForced(it.x, it.z, false) }
         }
-        val dragon = EnderDragon(EntityType.ENDER_DRAGON, end)
-        dragon.moveTo(0.0, 80.0, 0.0)
-        s.check(!end.addFreshEntity(dragon) || dragon.isRemoved) { "an Ender Dragon could join the End" }
-        val boss = EndBoss.spawn(end) ?: throw GameTestAssertException("the End boss didn't appear")
-        s.check(boss.pokemon.species.name.equals(BossDefs.end!!.end!!.species, ignoreCase = true) && boss.pokemon.isUncatchable()) {
-            "the End boss is a catchable ${boss.pokemon.species.name}"
-        }
-        val xp = player.totalExperience
-        EndBoss.defeated(end, listOf(player))
-        s.check(player.totalExperience > xp) { "no experience for beating the End boss" }
-        val area = BlockPos.betweenClosed(BlockPos(-4, 0, -4), BlockPos(4, 255, 4))
-        s.check(area.any { end.getBlockState(it).`is`(Blocks.END_PORTAL) }) { "no exit portal after the End boss was beaten" }
-        s.check(area.any { end.getBlockState(it).`is`(Blocks.DRAGON_EGG) }) { "no dragon egg after the first win" }
-        s.helper.succeed()
+        s.helper.startSequence()
+            .thenWaitUntil { s.check(chunks.all { end.areEntitiesLoaded(it.toLong()) }) { "the End's middle isn't loaded yet" } }
+            .thenExecute {
+                val dragon = EnderDragon(EntityType.ENDER_DRAGON, end)
+                dragon.moveTo(0.0, 80.0, 0.0)
+                s.check(!end.addFreshEntity(dragon) || dragon.isRemoved) { "an Ender Dragon could join the End" }
+                val boss = EndBoss.spawn(end) ?: throw GameTestAssertException("the End boss didn't appear")
+                s.check(boss.pokemon.species.name.equals(BossDefs.end!!.end!!.species, ignoreCase = true) && boss.pokemon.isUncatchable()) {
+                    "the End boss is a catchable ${boss.pokemon.species.name}"
+                }
+                // A second one may not join while the first is alive (Adrian saw one appear on each visit).
+                val second = EndBoss.spawn(end)
+                s.check(second == null || second.isRemoved) { "a second End boss joined beside the first" }
+                s.check(EndBoss.current(end) === boss) { "the End boss on record isn't the first one" }
+                val xp = player.totalExperience
+                EndBoss.defeated(end, listOf(player))
+                s.check(player.totalExperience > xp) { "no experience for beating the End boss" }
+                val area = BlockPos.betweenClosed(BlockPos(-4, 0, -4), BlockPos(4, 255, 4))
+                s.check(area.any { end.getBlockState(it).`is`(Blocks.END_PORTAL) }) { "no exit portal after the End boss was beaten" }
+                s.check(area.any { end.getBlockState(it).`is`(Blocks.DRAGON_EGG) }) { "no dragon egg after the first win" }
+                boss.discard()
+            }
+            .thenSucceed()
     }
 }