feat(border): add base boundary particles

README.md

@@ -31,6 +31,7 @@ The plugin JAR is written to `build/libs/`.
 /basesettings visitors <allowed|blocked>
 /basesettings navigation <enable|disable>
 /basesettings flight <enable|disable>
+/basesettings border <enable|disable>
 /basesettings bossbar <enable|disable>
 ```
 

design/log.md

@@ -69,3 +69,10 @@ description: Chronological record of material decisions affecting the Spigot Bas
 - Removed the unsafe unconfirmed base reset path; complete resets now require `reset <player> all confirm`.
 - Tightened argument validation and replaced implementation-specific enum errors with player-facing usage guidance.
 - Verified the administrative revision with `./gradlew clean check jar`.
+
+## 2026-08-10 — Base border visualization
+
+- Added persisted, owner-only base border particles controlled by `/basesettings border enable|disable` with contextual autocomplete.
+- Rendered a bounded nearby arc at the player's current height using the current base radius while respecting world and vertical bounds.
+- Added border preference reporting to player and administrative status output and safe defaults for existing state files.
+- Verified the feature with `./gradlew clean check jar`.

design/user-stories/index.md

@@ -18,3 +18,4 @@ description: Catalog of user stories for the Spigot Base plugin.
 10. [US-010: Administer player progression](us-010-administer-player-progression.md)
 11. [US-011: Configure and persist progression](us-011-configure-and-persist-progression.md)
 12. [US-012: Build and release the plugin](us-012-build-and-release-plugin.md)
+13. [US-013: Visualize the base border](us-013-visualize-base-border.md)

design/user-stories/us-013-visualize-base-border.md

@@ -0,0 +1,31 @@
+---
+type: User Story
+title: "US-013: Visualize the base border"
+description: Let players display a bounded, owner-only particle arc along the current edge of their established base.
+status: done
+---
+
+# US-013: Visualize the base border
+
+As a **player with Base I**, I want to display a particle effect at my base border so that I can understand where base benefits begin and end while building.
+
+## Acceptance criteria
+
+- [x] Border visualization requires Base I and an established base.
+- [x] `/basesettings border enable` enables visualization idempotently, and `/basesettings border disable` disables it idempotently.
+- [x] `border`, `enable`, and `disable` are offered through contextual autocomplete.
+- [x] Border visualization is disabled by default and the preference persists across reconnects and restarts.
+- [x] Older state files without the preference load it as disabled.
+- [x] `/basesettings status` and `/baseadmin status` display the border preference.
+- [x] Particles are visible only to the base owner.
+- [x] Particles trace the current circular horizontal boundary at the player's current Y-level and follow base expansion or relocation immediately.
+- [x] Particles render only while the player is in the base world, within the base's vertical range, and reasonably close to the boundary.
+- [x] Particle generation is bounded to avoid excessive server and client load.
+- [x] A complete administrative reset disables border visualization.
+
+## Related
+
+- [US-001: Unlock and establish Base I](us-001-unlock-and-establish-base.md)
+- [US-003: Expand the base](us-003-expand-the-base.md)
+- [US-009: View progression and unlock notifications](us-009-view-progression-and-notifications.md)
+- [US-010: Administer player progression](us-010-administer-player-progression.md)

src/main/java/games/dmg/spigotbase/BaseAdminCommand.java

@@ -97,8 +97,8 @@ final class BaseAdminCommand implements CommandExecutor, TabCompleter {
         sender.sendMessage(ChatColor.GRAY + "In-base placements=" + player.blocksPlacedInBase()
             + " breaks=" + player.blocksBrokenInBase());
         sender.sendMessage(ChatColor.GRAY + "Toggles: navigation=" + player.navigationEnabled()
-            + " flight=" + player.flightEnabled() + " bossbar=" + player.bossBarEnabled()
+            + " flight=" + player.flightEnabled() + " border=" + player.borderEnabled()
-            + " visitors=" + player.visitorsEnabled());
+            + " bossbar=" + player.bossBarEnabled() + " visitors=" + player.visitorsEnabled());
         sender.sendMessage(ChatColor.GRAY + "Base: " + player.base()
             .map(base -> base.worldName() + " " + base.x() + "," + base.y() + "," + base.z())
             .orElse("not set"));

src/main/java/games/dmg/spigotbase/BaseBorderController.java

@@ -0,0 +1,62 @@
+package games.dmg.spigotbase;
+
+import org.bukkit.Location;
+import org.bukkit.Particle;
+import org.bukkit.Server;
+import org.bukkit.entity.Player;
+
+final class BaseBorderController implements Runnable {
+    private final Server server;
+    private final BaseStateManager stateManager;
+    private final BaseBoundsService boundsService;
+
+    BaseBorderController(
+        Server server,
+        BaseStateManager stateManager,
+        BaseBoundsService boundsService
+    ) {
+        this.server = server;
+        this.stateManager = stateManager;
+        this.boundsService = boundsService;
+    }
+
+    @Override
+    public void run() {
+        for (Player player : server.getOnlinePlayers()) {
+            PlayerState state = stateManager.player(player.getUniqueId(), player.getName());
+            if (!state.borderEnabled() || state.base().isEmpty()) {
+                continue;
+            }
+            BaseLocation base = state.base().orElseThrow();
+            if (!player.getWorld().getUID().equals(base.worldId())) {
+                continue;
+            }
+            Location playerLocation = player.getLocation();
+            long minimumY = (long) base.y() - boundsService.verticalRange(state);
+            long maximumY = (long) base.y() + boundsService.verticalRange(state);
+            if (playerLocation.getY() < minimumY || playerLocation.getY() > maximumY) {
+                continue;
+            }
+            for (BaseBorderGeometry.Point point : BaseBorderGeometry.visiblePoints(
+                    base.x() + 0.5,
+                    base.z() + 0.5,
+                    boundsService.radius(state),
+                    playerLocation.getX(),
+                    playerLocation.getZ()
+            )) {
+                Location particle = new Location(
+                    player.getWorld(),
+                    point.x(),
+                    playerLocation.getY() + 0.15,
+                    point.z()
+                );
+                player.spawnParticle(
+                    Particle.END_ROD,
+                    particle,
+                    1,
+                    0.0, 0.0, 0.0, 0.0
+                );
+            }
+        }
+    }
+}

src/main/java/games/dmg/spigotbase/BaseBorderGeometry.java

@@ -0,0 +1,58 @@
+package games.dmg.spigotbase;
+
+import java.util.ArrayList;
+import java.util.List;
+
+final class BaseBorderGeometry {
+    static final int MAX_PARTICLES = 64;
+    static final double VISIBILITY_DISTANCE = 32.0;
+    private static final double PARTICLE_SPACING = 1.0;
+
+    private BaseBorderGeometry() {
+    }
+
+    static List<Point> visiblePoints(
+        double centerX,
+        double centerZ,
+        int radius,
+        double playerX,
+        double playerZ
+    ) {
+        if (radius <= 0) {
+            throw new IllegalArgumentException("border radius must be positive");
+        }
+        double playerRadius = Math.hypot(playerX - centerX, playerZ - centerZ);
+        if (Math.abs(playerRadius - radius) > VISIBILITY_DISTANCE) {
+            return List.of();
+        }
+
+        double circumference = 2.0 * Math.PI * radius;
+        int count = Math.min(MAX_PARTICLES, Math.max(1, (int) Math.ceil(
+            circumference / PARTICLE_SPACING
+        )));
+        double centerAngle = Math.atan2(playerZ - centerZ, playerX - centerX);
+        double angleStep = circumference <= MAX_PARTICLES * PARTICLE_SPACING
+            ? 2.0 * Math.PI / count
+            : PARTICLE_SPACING / radius;
+        double startAngle = circumference <= MAX_PARTICLES * PARTICLE_SPACING
+            ? 0.0
+            : centerAngle - angleStep * (count - 1) / 2.0;
+
+        List<Point> points = new ArrayList<>(count);
+        double visibilitySquared = VISIBILITY_DISTANCE * VISIBILITY_DISTANCE;
+        for (int index = 0; index < count; index++) {
+            double angle = startAngle + angleStep * index;
+            double x = centerX + radius * Math.cos(angle);
+            double z = centerZ + radius * Math.sin(angle);
+            double deltaX = x - playerX;
+            double deltaZ = z - playerZ;
+            if (deltaX * deltaX + deltaZ * deltaZ <= visibilitySquared) {
+                points.add(new Point(x, z));
+            }
+        }
+        return List.copyOf(points);
+    }
+
+    record Point(double x, double z) {
+    }
+}

src/main/java/games/dmg/spigotbase/BaseSettingsCommand.java

@@ -15,7 +15,7 @@ import org.bukkit.inventory.PlayerInventory;
 
 final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
     private static final List<String> SETTINGS = List.of(
-        "status", "upgrade", "visitors", "navigation", "flight", "bossbar"
+        "status", "upgrade", "visitors", "navigation", "flight", "border", "bossbar"
     );
     private static final List<String> VISITOR_MODES = List.of("allowed", "blocked");
     private static final List<String> ENABLE_MODES = List.of("enable", "disable");
@@ -59,6 +59,9 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
         if (arguments.length == 2 && arguments[0].equalsIgnoreCase("flight")) {
             return updateFlight(player, state, arguments[1]);
         }
+        if (arguments.length == 2 && arguments[0].equalsIgnoreCase("border")) {
+            return updateBorder(player, state, arguments[1]);
+        }
         if (arguments.length == 2 && arguments[0].equalsIgnoreCase("bossbar")) {
             return updateBossBar(player, arguments[1]);
         }
@@ -189,6 +192,29 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
         return true;
     }
 
+    private boolean updateBorder(Player player, PlayerState state, String mode) {
+        if (state.baseLevel() < 1 || state.base().isEmpty()) {
+            player.sendMessage(ChatColor.RED
+                + "Establish Base I before enabling border visualization.");
+            return true;
+        }
+        Boolean enabled = enabledMode(mode);
+        if (enabled == null) {
+            sendUsage(player);
+            return true;
+        }
+        state = stateManager.update(
+            player.getUniqueId(),
+            player.getName(),
+            current -> current.withBorderEnabled(enabled)
+        );
+        stateManager.saveIfDirty();
+        player.sendMessage(ChatColor.YELLOW + "Base border visualization is now "
+            + (state.borderEnabled() ? ChatColor.GREEN + "enabled" : ChatColor.RED + "disabled")
+            + ChatColor.YELLOW + ".");
+        return true;
+    }
+
     private boolean updateBossBar(Player player, String mode) {
         Boolean enabled = enabledMode(mode);
         if (enabled == null) {
@@ -218,6 +244,7 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
             + (state.visitorsEnabled() ? "allowed" : "blocked")
             + " navigation=" + (state.navigationEnabled() ? "enabled" : "disabled")
             + " flight=" + (state.flightEnabled() ? "enabled" : "disabled")
+            + " border=" + (state.borderEnabled() ? "enabled" : "disabled")
             + " bossbar=" + (state.bossBarEnabled() ? "enabled" : "disabled"));
         state.base().ifPresentOrElse(
             base -> player.sendMessage(ChatColor.GRAY + "Base: " + base.worldName() + " "
@@ -306,7 +333,7 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
             List<String> modes = arguments[0].equalsIgnoreCase("visitors")
                 ? VISITOR_MODES
                 : switch (arguments[0].toLowerCase(Locale.ROOT)) {
-                    case "navigation", "flight", "bossbar" -> ENABLE_MODES;
+                    case "navigation", "flight", "border", "bossbar" -> ENABLE_MODES;
                     default -> List.of();
                 };
             String prefix = arguments[1].toLowerCase(Locale.ROOT);
@@ -372,6 +399,6 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
     private static void sendUsage(Player player) {
         player.sendMessage(ChatColor.RED + "Usage: /basesettings "
             + "[status|upgrade|visitors <allowed|blocked>|navigation <enable|disable>"
-            + "|flight <enable|disable>|bossbar <enable|disable>]");
+            + "|flight <enable|disable>|border <enable|disable>|bossbar <enable|disable>]");
     }
 }

src/main/java/games/dmg/spigotbase/PlayerState.java

@@ -26,7 +26,8 @@ public record PlayerState(
     boolean visitorsEnabled,
     Optional<Instant> lastBaseSet,
     Optional<Instant> lastBaseTeleport,
-    Map<UUID, Instant> visitorCooldownUntil
+    Map<UUID, Instant> visitorCooldownUntil,
+    boolean borderEnabled
 ) {
     public PlayerState {
         if (playerId == null) {
@@ -69,12 +70,47 @@ public record PlayerState(
         if (baseLevel < 4 && visitorsEnabled) {
             throw new IllegalArgumentException("visitor access requires Base IV");
         }
+        if (borderEnabled && (baseLevel < 1 || base.isEmpty())) {
+            throw new IllegalArgumentException("border visualization requires an established Base I");
+        }
         if (visitorCooldownUntil.entrySet().stream().anyMatch(entry ->
                 entry.getKey() == null || entry.getValue() == null)) {
             throw new IllegalArgumentException("visitor cooldowns must be complete");
         }
     }
 
+    public PlayerState(
+        UUID playerId,
+        String latestName,
+        Optional<BaseLocation> base,
+        int baseLevel,
+        int sizeLevel,
+        int flightLevel,
+        int warmupLevel,
+        int cooldownLevel,
+        long grassAndDirtBroken,
+        long stoneBroken,
+        long deepslateBroken,
+        long obsidianBroken,
+        long blocksPlacedInBase,
+        long blocksBrokenInBase,
+        boolean navigationEnabled,
+        boolean flightEnabled,
+        boolean bossBarEnabled,
+        boolean visitorsEnabled,
+        Optional<Instant> lastBaseSet,
+        Optional<Instant> lastBaseTeleport,
+        Map<UUID, Instant> visitorCooldownUntil
+    ) {
+        this(
+            playerId, latestName, base, baseLevel, sizeLevel, flightLevel,
+            warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
+            obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
+            navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, false
+        );
+    }
+
     public static PlayerState newPlayer(UUID playerId, String latestName) {
         return new PlayerState(
             playerId,
@@ -93,7 +129,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -103,7 +139,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, count, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -113,7 +149,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, enabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -123,7 +159,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             enabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -133,7 +169,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stone, deepslate,
             obsidian, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -143,7 +179,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, enabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -163,7 +199,7 @@ public record PlayerState(
             newWarmupLevel, newCooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, placements, breaks,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -179,7 +215,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, Optional.of(usedAt), visitorCooldownUntil
+            lastBaseSet, Optional.of(usedAt), visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -189,7 +225,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -206,7 +242,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassDirt, stone, deepslate,
             obsidian, placements, baseBreaks,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -225,7 +261,8 @@ public record PlayerState(
             newWarmupLevel, newCooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             newNavigationEnabled, newFlightEnabled, bossBarEnabled, newVisitorsEnabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil,
+            borderEnabled && newBaseLevel >= 1 && base.isPresent()
         );
     }
 
@@ -235,7 +272,17 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, enabled,
-            lastBaseSet, lastBaseTeleport, visitorCooldownUntil
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, borderEnabled
+        );
+    }
+
+    public PlayerState withBorderEnabled(boolean enabled) {
+        return new PlayerState(
+            playerId, latestName, base, baseLevel, sizeLevel, flightLevel,
+            warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
+            obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
+            navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
+            lastBaseSet, lastBaseTeleport, visitorCooldownUntil, enabled
         );
     }
 
@@ -247,7 +294,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, cooldowns
+            lastBaseSet, lastBaseTeleport, cooldowns, borderEnabled
         );
     }
 
@@ -257,7 +304,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, Optional.empty(), visitorCooldownUntil
+            lastBaseSet, Optional.empty(), visitorCooldownUntil, borderEnabled
         );
     }
 
@@ -267,7 +314,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            lastBaseSet, lastBaseTeleport, Map.of()
+            lastBaseSet, lastBaseTeleport, Map.of(), borderEnabled
         );
     }
 
@@ -277,7 +324,7 @@ public record PlayerState(
             warmupLevel, cooldownLevel, grassAndDirtBroken, stoneBroken, deepslateBroken,
             obsidianBroken, blocksPlacedInBase, blocksBrokenInBase,
             navigationEnabled, flightEnabled, bossBarEnabled, visitorsEnabled,
-            Optional.of(setAt), lastBaseTeleport, visitorCooldownUntil
+            Optional.of(setAt), lastBaseTeleport, visitorCooldownUntil, borderEnabled
         );
     }
 

src/main/java/games/dmg/spigotbase/SpigotBasePlugin.java

@@ -91,6 +91,12 @@ public final class SpigotBasePlugin extends JavaPlugin {
             10L,
             10L
         );
+        getServer().getScheduler().runTaskTimer(
+            this,
+            new BaseBorderController(getServer(), stateManager, boundsService),
+            10L,
+            10L
+        );
         getServer().getScheduler().runTaskTimer(this, flightController, 5L, 5L);
         getServer().getScheduler().runTaskTimer(this, stateManager::saveIfDirty, 600L, 600L);
         getLogger().info("Spigot Base enabled.");

src/main/java/games/dmg/spigotbase/YamlBaseStateRepository.java

@@ -127,7 +127,8 @@ public final class YamlBaseStateRepository {
                     yaml.getBoolean(path + ".visitors-enabled", false),
                     instant(yaml, path + ".last-base-set-epoch-millis"),
                     instant(yaml, path + ".last-base-teleport-epoch-millis"),
-                    loadVisitorCooldowns(yaml, path + ".visitor-cooldowns")
+                    loadVisitorCooldowns(yaml, path + ".visitor-cooldowns"),
+                    yaml.getBoolean(path + ".border-enabled", false)
                 );
                 players.put(playerId, player);
             } catch (IllegalArgumentException ignored) {
@@ -222,6 +223,7 @@ public final class YamlBaseStateRepository {
             yaml.set(path + ".flight-enabled", player.flightEnabled());
             yaml.set(path + ".boss-bar-enabled", player.bossBarEnabled());
             yaml.set(path + ".visitors-enabled", player.visitorsEnabled());
+            yaml.set(path + ".border-enabled", player.borderEnabled());
             yaml.set(
                 path + ".last-base-set-epoch-millis",
                 player.lastBaseSet().map(Instant::toEpochMilli).orElse(null)

src/main/resources/plugin.yml

@@ -19,7 +19,7 @@ commands:
     aliases: [visit]
   basesettings:
     description: View progression, upgrade, and manage base settings.
-    usage: /basesettings [status|upgrade|visitors|navigation|flight|bossbar]
+    usage: /basesettings [status|upgrade|visitors|navigation|flight|border|bossbar]
     aliases: [homesettings]
   baseadmin:
     description: Administer Spigot Base.

src/test/java/games/dmg/spigotbase/AdminProgressionServiceTest.java

@@ -4,6 +4,7 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.time.Instant;
 import java.util.UUID;
 import org.junit.jupiter.api.Test;
 
@@ -36,6 +37,22 @@ final class AdminProgressionServiceTest {
         assertFalse(updated.visitorsEnabled());
     }
 
+    @Test
+    void loweringBaseDisablesBorderVisualization() {
+        UUID playerId = UUID.randomUUID();
+        PlayerState player = PlayerState.newPlayer(playerId, "Alex")
+            .withAdministrativeLevels(1, 0, 0, 0, 0, false, false, false)
+            .withBase(
+                new BaseLocation(UUID.randomUUID(), "world", 0, 64, 0, 0, 0),
+                Instant.EPOCH
+            )
+            .withBorderEnabled(true);
+
+        PlayerState updated = service.setLevel(player, ProgressionPath.BASE, 0);
+
+        assertFalse(updated.borderEnabled());
+    }
+
     @Test
     void rejectsUnknownLevel() {
         PlayerState player = PlayerState.newPlayer(UUID.randomUUID(), "Alex");

src/test/java/games/dmg/spigotbase/BaseBorderControllerTest.java

@@ -0,0 +1,92 @@
+package games.dmg.spigotbase;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.atLeastOnce;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.time.Instant;
+import java.util.Map;
+import java.util.UUID;
+import org.bukkit.Location;
+import org.bukkit.Particle;
+import org.bukkit.Server;
+import org.bukkit.World;
+import org.bukkit.entity.Player;
+import org.junit.jupiter.api.Test;
+
+final class BaseBorderControllerTest {
+    @Test
+    void doesNotRenderOutsideTheBaseVerticalRange() {
+        UUID playerId = UUID.randomUUID();
+        UUID worldId = UUID.randomUUID();
+        PlayerState state = PlayerState.newPlayer(playerId, "Builder")
+            .withAdministrativeLevels(1, 0, 0, 0, 0, false, false, false)
+            .withBase(new BaseLocation(worldId, "world", 0, 64, 0, 0, 0), Instant.EPOCH)
+            .withBorderEnabled(true);
+
+        World world = mock(World.class);
+        when(world.getUID()).thenReturn(worldId);
+        Player player = mock(Player.class);
+        when(player.getUniqueId()).thenReturn(playerId);
+        when(player.getName()).thenReturn("Builder");
+        when(player.getWorld()).thenReturn(world);
+        when(player.getLocation()).thenReturn(new Location(world, 10.5, 100.0, 0.5));
+        Server server = mock(Server.class);
+        doReturn(java.util.List.of(player)).when(server).getOnlinePlayers();
+        BaseStateManager stateManager = mock(BaseStateManager.class);
+        when(stateManager.player(playerId, "Builder")).thenReturn(state);
+
+        new BaseBorderController(
+            server,
+            stateManager,
+            new BaseBoundsService(PluginSettings.from(Map.of()))
+        ).run();
+
+        verify(player, never()).spawnParticle(
+            eq(Particle.END_ROD),
+            any(Location.class),
+            eq(1),
+            eq(0.0), eq(0.0), eq(0.0), eq(0.0)
+        );
+    }
+
+    @Test
+    void ownerSeesParticlesAtCurrentHeightNearEnabledBorder() {
+        UUID playerId = UUID.randomUUID();
+        UUID worldId = UUID.randomUUID();
+        PlayerState state = PlayerState.newPlayer(playerId, "Builder")
+            .withAdministrativeLevels(1, 0, 0, 0, 0, false, false, false)
+            .withBase(new BaseLocation(worldId, "world", 0, 64, 0, 0, 0), Instant.EPOCH)
+            .withBorderEnabled(true);
+
+        World world = mock(World.class);
+        when(world.getUID()).thenReturn(worldId);
+        Player player = mock(Player.class);
+        when(player.getUniqueId()).thenReturn(playerId);
+        when(player.getName()).thenReturn("Builder");
+        when(player.getWorld()).thenReturn(world);
+        when(player.getLocation()).thenReturn(new Location(world, 10.5, 70.0, 0.5));
+        Server server = mock(Server.class);
+        doReturn(java.util.List.of(player)).when(server).getOnlinePlayers();
+        BaseStateManager stateManager = mock(BaseStateManager.class);
+        when(stateManager.player(playerId, "Builder")).thenReturn(state);
+
+        new BaseBorderController(
+            server,
+            stateManager,
+            new BaseBoundsService(PluginSettings.from(Map.of()))
+        ).run();
+
+        verify(player, atLeastOnce()).spawnParticle(
+            eq(Particle.END_ROD),
+            any(Location.class),
+            eq(1),
+            eq(0.0), eq(0.0), eq(0.0), eq(0.0)
+        );
+    }
+}

src/test/java/games/dmg/spigotbase/BaseBorderGeometryTest.java

@@ -0,0 +1,27 @@
+package games.dmg.spigotbase;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+final class BaseBorderGeometryTest {
+    @Test
+    void producesBoundedPointsOnTheCurrentCircularBoundary() {
+        List<BaseBorderGeometry.Point> points = BaseBorderGeometry.visiblePoints(
+            0.5, 0.5, 150, 150.5, 0.5
+        );
+
+        assertFalse(points.isEmpty());
+        assertTrue(points.size() <= BaseBorderGeometry.MAX_PARTICLES);
+        assertTrue(points.stream().allMatch(point ->
+            Math.abs(Math.hypot(point.x() - 0.5, point.z() - 0.5) - 150.0) < 0.0001
+        ));
+    }
+
+    @Test
+    void omitsParticlesWhenPlayerIsFarFromBoundary() {
+        assertTrue(BaseBorderGeometry.visiblePoints(0.5, 0.5, 10, 100.5, 0.5).isEmpty());
+    }
+}

src/test/java/games/dmg/spigotbase/BaseSettingsCommandTest.java

@@ -24,6 +24,21 @@ import org.bukkit.inventory.PlayerInventory;
 import org.junit.jupiter.api.Test;
 
 final class BaseSettingsCommandTest {
+    @Test
+    void borderEnableIsIdempotent() {
+        UUID playerId = UUID.randomUUID();
+        PlayerState current = PlayerState.newPlayer(playerId, "Builder")
+            .withAdministrativeLevels(1, 0, 0, 0, 0, false, false, false)
+            .withBase(
+                new BaseLocation(UUID.randomUUID(), "world", 0, 64, 0, 0, 0),
+                Instant.EPOCH
+            );
+
+        CommandResult result = execute(current, "border", "enable");
+
+        assertTrue(result.updated().borderEnabled());
+    }
+
     @Test
     void invalidArgumentsShowUsage() {
         UUID playerId = UUID.randomUUID();
@@ -58,7 +73,7 @@ final class BaseSettingsCommandTest {
             List.of("allowed"),
             command.onTabComplete(null, null, "basesettings", new String[] {"visitors", "a"})
         );
-        for (String setting : List.of("navigation", "flight", "bossbar")) {
+        for (String setting : List.of("navigation", "flight", "border", "bossbar")) {
             assertEquals(
                 List.of("disable"),
                 command.onTabComplete(null, null, "basesettings", new String[] {setting, "d"})
@@ -75,7 +90,7 @@ final class BaseSettingsCommandTest {
         );
 
         assertEquals(
-            List.of("status", "upgrade", "visitors", "navigation", "flight", "bossbar"),
+            List.of("status", "upgrade", "visitors", "navigation", "flight", "border", "bossbar"),
             command.onTabComplete(null, null, "basesettings", new String[] {""})
         );
     }
@@ -194,6 +209,7 @@ final class BaseSettingsCommandTest {
             message.contains("Settings: visitors=")
                 && message.contains("navigation=")
                 && message.contains("flight=")
+                && message.contains("border=")
                 && message.contains("bossbar=")
             )
         );

src/test/java/games/dmg/spigotbase/PlayerStateTest.java

@@ -1,13 +1,31 @@
 package games.dmg.spigotbase;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.time.Instant;
 import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
 import org.junit.jupiter.api.Test;
 
 final class PlayerStateTest {
+    @Test
+    void borderVisualizationIsDisabledByDefaultAndCanBeEnabled() {
+        UUID playerId = UUID.randomUUID();
+        PlayerState player = PlayerState.newPlayer(playerId, "Alex");
+        PlayerState established = player
+            .withAdministrativeLevels(1, 0, 0, 0, 0, false, false, false)
+            .withBase(
+                new BaseLocation(UUID.randomUUID(), "world", 0, 64, 0, 0, 0),
+                Instant.EPOCH
+            );
+
+        assertFalse(player.borderEnabled());
+        assertTrue(established.withBorderEnabled(true).borderEnabled());
+    }
+
     @Test
     void rejectsLevelsOutsideKnownRanges() {
         UUID playerId = UUID.randomUUID();

src/test/java/games/dmg/spigotbase/YamlBaseStateRepositoryTest.java

@@ -28,7 +28,8 @@ final class YamlBaseStateRepositoryTest {
             true, true, false, true,
             Optional.of(Instant.ofEpochMilli(1_750_000_000_000L)),
             Optional.of(Instant.ofEpochMilli(1_750_000_100_000L)),
-            Map.of(ownerId, Instant.ofEpochMilli(1_750_001_000_000L))
+            Map.of(ownerId, Instant.ofEpochMilli(1_750_001_000_000L)),
+            true
         );
         PersistentState expected = new PersistentState(Map.of(playerId, player));
         YamlBaseStateRepository repository =
@@ -39,6 +40,24 @@ final class YamlBaseStateRepositoryTest {
         assertEquals(expected, repository.load());
     }
 
+    @Test
+    void olderStateWithoutBorderPreferenceDefaultsToDisabled() throws Exception {
+        UUID playerId = UUID.randomUUID();
+        Path stateFile = temporaryDirectory.resolve("state.yml");
+        Files.writeString(stateFile, """
+            players:
+              %s:
+                name: Alex
+            """.formatted(playerId));
+
+        PlayerState player = new YamlBaseStateRepository(stateFile)
+            .load()
+            .players()
+            .get(playerId);
+
+        assertFalse(player.borderEnabled());
+    }
+
     @Test
     void invalidRecordsCannotGrantProgression() throws Exception {
         UUID playerId = UUID.randomUUID();