feat(commands): manage height bounds with tab completion

README.md

@@ -64,6 +64,22 @@ launcher:
 
 Player scales are stored by UUID in `plugins/SpigotHeights/state.yml`.
 
+## Commands
+
+Operators (or senders granted `spigotheights.admin`) can use:
+
+```text
+/heights settings
+/heights set min 0.2
+/heights set max 3.0
+```
+
+Console is supported. Tab completion suggests subcommands, bound names, and valid example values; other valid numbers may also be entered.
+
+Changes are saved to `plugins/SpigotHeights/config.yml` and take effect without a restart. Minimum must be at least `0.0625`, maximum at most `16.0`, minimum cannot exceed maximum, and the launcher threshold must remain within the range. Invalid changes or save failures leave active settings unchanged.
+
+Players are not immediately resized. Subsequent potion use, joins, and respawns use the new limits; Restoration still returns and preserves exact scale `1.0`. These commands only change min/max; edit other settings in the configuration file and restart the server.
+
 ## Build
 
 ```bash

design/log.md

@@ -6,6 +6,18 @@ description: Chronological record of material decisions affecting Spigot Heights
 
 # Spigot Heights Design Log
 
+## 2026-09-06T23:51:22Z — Settings commands completed
+
+- Added `/heights settings` and `/heights set min|max <value>` with `spigotheights.admin` (default op), generic sender support, and prefix-filtered tab completion of valid example values.
+- Validated changes are persisted through temporary-file replacement (atomic where supported) before activating shared live settings. Unrelated YAML values are preserved; malformed files and write failures do not activate new limits.
+- Updated gameplay listeners to read current settings without immediately resizing players or resetting launcher cooldowns.
+- Verified `./gradlew clean check jar`: all 26 tests passed. Inspected command registration and event wiring; live-server/client verification remains unperformed. Completed US-007 and the related US-004 change.
+
+## 2026-09-06T23:45:28Z — Settings commands approved and started
+
+- Approved [US-007](user-stories/us-007-manage-settings-commands.md): permission-protected min/max commands, tab completion, validation, and persistent live updates.
+- Existing players are not resized immediately; subsequent gameplay reads current limits. The exact `1.0` restoration exception remains intact.
+
 ## 2026-09-06T23:41:16Z — Restoration completed
 
 - Added the white Potion of Restoration with persistent identity and the approved Sugar upgrade recipe.

design/user-stories/index.md

@@ -12,3 +12,4 @@ description: Catalog of user stories for the Spigot Heights plugin.
 4. [US-004: Configure and persist stature behavior](us-004-configure-and-persist.md)
 5. [US-005: Build and release the plugin](us-005-build-and-release.md)
 6. [US-006: Restore default stature](us-006-restore-default-stature.md)
+7. [US-007: Manage stature settings with commands](us-007-manage-settings-commands.md)

design/user-stories/us-004-configure-and-persist.md

@@ -19,8 +19,10 @@ As a **server operator**, I want validated stature and launcher settings with du
 - [x] Missing state defaults safely to scale `1.0` clamped to the configured range.
 - [x] Saved out-of-range state is clamped before it is applied, except exact scale `1.0`, which is preserved for restoration.
 - [x] Configuration and state behavior have automated tests.
+- [x] Approved min/max commands validate and persist changes before publishing live settings to gameplay listeners, without immediately resizing players.
 
 ## Related
 
 - [User-story catalog](index.md)
+- [US-007: Manage stature settings with commands](us-007-manage-settings-commands.md)
 - [US-006: Restore default stature](us-006-restore-default-stature.md)

design/user-stories/us-007-manage-settings-commands.md

@@ -0,0 +1,30 @@
+---
+type: User Story
+title: "US-007: Manage stature settings with commands"
+description: Let administrators view and persistently change stature bounds with tab-completed commands.
+status: done
+---
+
+# US-007: Manage stature settings with commands
+
+As a **server administrator**, I want commands with tab completion so that I can change stature limits without restarting the server.
+
+## Acceptance criteria
+
+- [x] `/heights settings` displays current settings; `/heights set min|max <value>` changes the selected bound.
+- [x] Operators and senders with `spigotheights.admin` may use the commands, including console; unauthorized senders cannot change settings or receive suggestions.
+- [x] Tab completion suggests subcommands, `min`/`max`, and valid example values, filtered by the typed prefix.
+- [x] Successful changes apply immediately to gameplay and persist to `plugins/SpigotHeights/config.yml` without discarding unrelated configuration.
+- [x] Invalid arguments or settings produce clear explanations and leave active and saved settings unchanged; persistence failure does not activate the new settings.
+- [x] Existing players are not immediately resized; subsequent potion use, joins, and respawns use current limits, preserving the restoration exception for `1.0`.
+- [x] Automated tests and README documentation cover commands, permissions, completion, validation, persistence, and live settings.
+
+## Verification
+
+- `./gradlew clean check jar` passed all 26 tests, including command execution with authorized/unauthorized generic senders, prefix-filtered valid completions, argument validation, failed saves, YAML reload/preservation, and live domain behavior.
+- Code inspection confirms command/permission registration and shared settings suppliers in consumption, join, respawn, and launcher adapters. No live-server command or client tab-completion test was performed.
+
+## Related
+
+- [US-004: Configure and persist stature behavior](us-004-configure-and-persist.md)
+- [US-006: Restore default stature](us-006-restore-default-stature.md)

src/main/java/games/dmg/spigotheights/HeightsCommand.java

@@ -0,0 +1,97 @@
+package games.dmg.spigotheights;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Locale;
+import java.util.logging.Logger;
+import java.util.stream.Stream;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+
+public final class HeightsCommand implements TabExecutor {
+    private static final String PERMISSION = "spigotheights.admin";
+    private static final String USAGE = "Usage: /heights settings | /heights set min|max <value>";
+    private final LiveHeightSettings settings;
+    private final Logger logger;
+
+    public HeightsCommand(LiveHeightSettings settings, Logger logger) {
+        this.settings = settings;
+        this.logger = logger;
+    }
+
+    @Override
+    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
+        if (!sender.hasPermission(PERMISSION)) {
+            sender.sendMessage("You do not have permission to manage Spigot Heights settings.");
+            return true;
+        }
+        if (args.length == 1 && args[0].equalsIgnoreCase("settings")) {
+            HeightSettings current = settings.get();
+            sender.sendMessage("Spigot Heights: min=" + current.minimum() + ", max=" + current.maximum()
+                    + ", adjustment-step=" + current.adjustmentStep()
+                    + ", launcher-threshold=" + current.launcherThreshold()
+                    + ", launcher-speed=" + current.launcherSpeed()
+                    + ", launcher-cooldown-ticks=" + current.launcherCooldownTicks());
+            return true;
+        }
+        if (args.length != 3 || !args[0].equalsIgnoreCase("set") || !isBound(args[1])) {
+            sender.sendMessage(USAGE);
+            return true;
+        }
+        try {
+            String bound = args[1].toLowerCase(Locale.ROOT);
+            double value = Double.parseDouble(args[2]);
+            settings.setBound(bound, value);
+            sender.sendMessage("Set " + bound + " to " + value + ". Saved and active; existing players were not resized.");
+        } catch (NumberFormatException exception) {
+            sender.sendMessage("Invalid value: enter a finite number, for example 0.2 or 3.0.");
+        } catch (IllegalArgumentException exception) {
+            sender.sendMessage("Invalid settings: " + exception.getMessage());
+        } catch (IOException exception) {
+            logger.warning("Could not save height settings: " + exception.getMessage());
+            sender.sendMessage("Could not save settings. Active settings are unchanged; check the server log.");
+        }
+        return true;
+    }
+
+    @Override
+    public List<String> onTabComplete(CommandSender sender, Command command, String alias, String[] args) {
+        if (!sender.hasPermission(PERMISSION)) {
+            return List.of();
+        }
+        if (args.length == 1) {
+            return matching(Stream.of("settings", "set"), args[0]);
+        }
+        if (args.length == 2 && args[0].equalsIgnoreCase("set")) {
+            return matching(Stream.of("min", "max"), args[1]);
+        }
+        if (args.length == 3 && args[0].equalsIgnoreCase("set") && isBound(args[1])) {
+            String bound = args[1].toLowerCase(Locale.ROOT);
+            HeightSettings current = settings.get();
+            return matching(Stream.of(current.minimum(), current.maximum(), current.launcherThreshold(),
+                            0.0625, 0.2, 0.4, 0.5, 1.0, 2.0, 3.0, 16.0)
+                    .distinct().sorted().filter(value -> isValid(bound, value)).map(String::valueOf), args[2]);
+        }
+        // Never fall back to Bukkit's player-name completion.
+        return List.of();
+    }
+
+    private boolean isValid(String bound, double value) {
+        try {
+            settings.candidate(bound, value);
+            return true;
+        } catch (IllegalArgumentException exception) {
+            return false;
+        }
+    }
+
+    private static boolean isBound(String value) {
+        return value.equalsIgnoreCase("min") || value.equalsIgnoreCase("max");
+    }
+
+    private static List<String> matching(Stream<String> candidates, String prefix) {
+        String normalized = prefix.toLowerCase(Locale.ROOT);
+        return candidates.filter(value -> value.startsWith(normalized)).toList();
+    }
+}

src/main/java/games/dmg/spigotheights/LiveHeightSettings.java

@@ -0,0 +1,42 @@
+package games.dmg.spigotheights;
+
+import java.io.IOException;
+import java.util.function.Supplier;
+
+/** Server-thread settings shared by commands and gameplay listeners. */
+public final class LiveHeightSettings implements Supplier<HeightSettings> {
+    @FunctionalInterface
+    public interface Saver {
+        void save(HeightSettings settings) throws IOException;
+    }
+
+    private HeightSettings current;
+    private final Saver saver;
+
+    public LiveHeightSettings(HeightSettings initial, Saver saver) {
+        this.current = initial;
+        this.saver = saver;
+    }
+
+    @Override
+    public HeightSettings get() {
+        return current;
+    }
+
+    public HeightSettings candidate(String bound, double value) {
+        if (!bound.equals("min") && !bound.equals("max")) {
+            throw new IllegalArgumentException("Choose min or max.");
+        }
+        return new HeightSettings(
+                bound.equals("min") ? value : current.minimum(),
+                bound.equals("max") ? value : current.maximum(),
+                current.adjustmentStep(), current.launcherThreshold(),
+                current.launcherSpeed(), current.launcherCooldownTicks());
+    }
+
+    public void setBound(String bound, double value) throws IOException {
+        HeightSettings next = candidate(bound, value);
+        saver.save(next);
+        current = next;
+    }
+}

src/main/java/games/dmg/spigotheights/SettingsFileStore.java

@@ -0,0 +1,41 @@
+package games.dmg.spigotheights;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.AtomicMoveNotSupportedException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
+import org.bukkit.configuration.InvalidConfigurationException;
+import org.bukkit.configuration.file.YamlConfiguration;
+
+public final class SettingsFileStore {
+    private final Path path;
+
+    public SettingsFileStore(Path path) {
+        this.path = path.toAbsolutePath();
+    }
+
+    public void save(HeightSettings settings) throws IOException {
+        // Read a separate document so failed writes cannot mutate the active configuration.
+        YamlConfiguration config = new YamlConfiguration();
+        try {
+            config.load(path.toFile());
+        } catch (InvalidConfigurationException exception) {
+            throw new IOException("Existing config.yml is invalid; refusing to overwrite it", exception);
+        }
+        config.set("height.minimum", settings.minimum());
+        config.set("height.maximum", settings.maximum());
+        Path temporary = Files.createTempFile(path.getParent(), "config-", ".yml.tmp");
+        try {
+            Files.writeString(temporary, config.saveToString(), StandardCharsets.UTF_8);
+            try {
+                Files.move(temporary, path, StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
+            } catch (AtomicMoveNotSupportedException exception) {
+                Files.move(temporary, path, StandardCopyOption.REPLACE_EXISTING);
+            }
+        } finally {
+            Files.deleteIfExists(temporary);
+        }
+    }
+}

src/main/java/games/dmg/spigotheights/SpigotHeightsPlugin.java

@@ -1,5 +1,7 @@
 package games.dmg.spigotheights;
 
+import java.util.Objects;
+import org.bukkit.command.PluginCommand;
 import org.bukkit.configuration.file.FileConfiguration;
 import org.bukkit.plugin.java.JavaPlugin;
 
@@ -16,12 +18,23 @@ public final class SpigotHeightsPlugin extends JavaPlugin {
             return;
         }
 
+        SettingsFileStore configStore = new SettingsFileStore(getDataFolder().toPath().resolve("config.yml"));
+        LiveHeightSettings liveSettings = new LiveHeightSettings(settings, next -> {
+            configStore.save(next);
+            getConfig().set("height.minimum", next.minimum());
+            getConfig().set("height.maximum", next.maximum());
+        });
+        HeightsCommand executor = new HeightsCommand(liveSettings, getLogger());
+        PluginCommand command = Objects.requireNonNull(getCommand("heights"), "Missing heights command declaration");
+        command.setExecutor(executor);
+        command.setTabCompleter(executor);
+
         HeightStore store = new HeightStore(getDataFolder());
         PotionRecipes potions = new PotionRecipes(this);
         potions.register();
         getServer().getPluginManager().registerEvents(
-                new StatureListener(this, settings, store, potions), this);
+                new StatureListener(this, liveSettings, store, potions), this);
-        getServer().getPluginManager().registerEvents(new TinyPlayerLauncher(settings), this);
+        getServer().getPluginManager().registerEvents(new TinyPlayerLauncher(liveSettings), this);
         getLogger().info("Spigot Heights enabled.");
     }
 

src/main/java/games/dmg/spigotheights/StatureListener.java

@@ -2,6 +2,7 @@ package games.dmg.spigotheights;
 
 import java.io.IOException;
 import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.Supplier;
 import org.bukkit.attribute.Attribute;
 import org.bukkit.attribute.AttributeInstance;
 import org.bukkit.entity.Player;
@@ -19,11 +20,11 @@ import org.bukkit.plugin.java.JavaPlugin;
 
 public final class StatureListener implements Listener {
     private final JavaPlugin plugin;
-    private final HeightSettings settings;
+    private final Supplier<HeightSettings> settings;
     private final HeightStore store;
     private final PotionRecipes potions;
 
-    public StatureListener(JavaPlugin plugin, HeightSettings settings, HeightStore store, PotionRecipes potions) {
+    public StatureListener(JavaPlugin plugin, Supplier<HeightSettings> settings, HeightStore store, PotionRecipes potions) {
         this.plugin = plugin;
         this.settings = settings;
         this.store = store;
@@ -50,7 +51,7 @@ public final class StatureListener implements Listener {
         }
         Player player = event.getPlayer();
         double current = currentScale(player);
-        double scale = kind.scaleAfterDrinking(current, settings,
+        double scale = kind.scaleAfterDrinking(current, settings.get(),
                 bound -> ThreadLocalRandom.current().nextInt(bound));
         applyAndSave(player, scale);
         player.sendMessage("Your scale is now " + scale + ".");
@@ -58,14 +59,14 @@ public final class StatureListener implements Listener {
 
     @EventHandler
     public void onJoin(PlayerJoinEvent event) {
-        apply(event.getPlayer(), HeightMath.safeStoredScale(store.find(event.getPlayer().getUniqueId()), settings));
+        apply(event.getPlayer(), HeightMath.safeStoredScale(store.find(event.getPlayer().getUniqueId()), settings.get()));
     }
 
     @EventHandler
     public void onRespawn(PlayerRespawnEvent event) {
         plugin.getServer().getScheduler().runTask(plugin, () -> {
             Player player = event.getPlayer();
-            apply(player, HeightMath.safeStoredScale(store.find(player.getUniqueId()), settings));
+            apply(player, HeightMath.safeStoredScale(store.find(player.getUniqueId()), settings.get()));
         });
     }
 

src/main/java/games/dmg/spigotheights/TinyPlayerLauncher.java

@@ -3,6 +3,7 @@ package games.dmg.spigotheights;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;
+import java.util.function.Supplier;
 import org.bukkit.Bukkit;
 import org.bukkit.Location;
 import org.bukkit.Material;
@@ -19,11 +20,11 @@ import org.bukkit.event.player.PlayerMoveEvent;
 import org.bukkit.util.Vector;
 
 public final class TinyPlayerLauncher implements Listener {
-    private final HeightSettings settings;
+    private final Supplier<HeightSettings> settingsSupplier;
     private final Map<UUID, Long> lastLaunchTicks = new HashMap<>();
 
-    public TinyPlayerLauncher(HeightSettings settings) {
+    public TinyPlayerLauncher(Supplier<HeightSettings> settingsSupplier) {
-        this.settings = settings;
+        this.settingsSupplier = settingsSupplier;
     }
 
     @EventHandler(ignoreCancelled = true)
@@ -32,6 +33,7 @@ public final class TinyPlayerLauncher implements Listener {
         if (destination == null || sameBlock(event.getFrom(), destination)) {
             return;
         }
+        HeightSettings settings = settingsSupplier.get();
         Player player = event.getPlayer();
         if (!LauncherPolicy.isSmallEnough(scale(player), settings.launcherThreshold())) {
             return;

src/main/resources/plugin.yml

@@ -4,3 +4,12 @@ main: games.dmg.spigotheights.SpigotHeightsPlugin
 api-version: "1.21"
 description: Craftable player stature potions and tiny-player dispenser launchers.
 author: dmg.games
+commands:
+  heights:
+    description: View and change Spigot Heights stature limits.
+    usage: /heights settings | /heights set min|max <value>
+    permission: spigotheights.admin
+permissions:
+  spigotheights.admin:
+    description: View and change Spigot Heights settings.
+    default: op

src/test/java/games/dmg/spigotheights/HeightsCommandTest.java

@@ -0,0 +1,111 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.lang.reflect.Proxy;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.logging.Logger;
+import org.bukkit.command.CommandSender;
+import org.junit.jupiter.api.Test;
+
+class HeightsCommandTest {
+    private final List<HeightSettings> saved = new ArrayList<>();
+    private final List<String> messages = new ArrayList<>();
+    private final LiveHeightSettings live = new LiveHeightSettings(
+            new HeightSettings(0.4, 2.0, 0.1, 0.5, 1.5, 20), saved::add);
+    private final HeightsCommand command = new HeightsCommand(live, Logger.getAnonymousLogger());
+
+    @Test
+    void authorizedSenderCanInspectAndChangeBounds() {
+        CommandSender sender = sender(true);
+        command.onCommand(sender, null, "heights", new String[] {"settings"});
+        assertTrue(messages.getLast().contains("min=0.4"));
+        assertTrue(messages.getLast().contains("max=2.0"));
+        command.onCommand(sender, null, "heights", new String[] {"set", "min", "0.2"});
+        command.onCommand(sender, null, "heights", new String[] {"set", "max", "3"});
+        assertEquals(0.2, live.get().minimum());
+        assertEquals(3.0, live.get().maximum());
+        assertEquals(2, saved.size());
+        assertTrue(messages.getLast().contains("3.0"));
+    }
+
+    @Test
+    void unauthorizedSenderCannotInspectMutateOrComplete() {
+        CommandSender sender = sender(false);
+        command.onCommand(sender, null, "heights", new String[] {"set", "min", "0.2"});
+        command.onCommand(sender, null, "heights", new String[] {"settings"});
+        assertTrue(messages.stream().allMatch(message -> message.contains("permission")));
+        assertEquals(List.of(), saved);
+        assertEquals(List.of(), command.onTabComplete(sender, null, "heights", new String[] {""}));
+    }
+
+    @Test
+    void malformedAndInvalidInputNeverSaves() {
+        for (String[] args : new String[][] {
+                {}, {"set"}, {"set", "min"}, {"set", "min", "0.2", "extra"},
+                {"settings", "extra"}, {"unknown"}, {"set", "speed", "1"},
+                {"set", "min", "nope"}, {"set", "min", "NaN"},
+                {"set", "max", "Infinity"}, {"set", "min", "0.6"}, {"set", "max", "0.3"}}) {
+            int before = messages.size();
+            assertTrue(command.onCommand(sender(true), null, "heights", args));
+            assertEquals(before + 1, messages.size());
+        }
+        assertEquals(List.of(), saved);
+        assertEquals(0.4, live.get().minimum());
+        assertEquals(2.0, live.get().maximum());
+    }
+
+    @Test
+    void completionsArePrefixFilteredAndValidForCurrentRange() throws Exception {
+        CommandSender sender = sender(true);
+        assertEquals(List.of("settings", "set"), complete(sender, "s"));
+        assertEquals(List.of("settings"), complete(sender, "sett"));
+        assertEquals(List.of("min", "max"), complete(sender, "set", "m"));
+        assertEquals(List.of("max"), complete(sender, "set", "ma"));
+        assertEquals(List.of(), complete(sender, "settings", ""));
+        assertEquals(List.of(), complete(sender, "set", "other", ""));
+        assertEquals(List.of(), complete(sender, "set", "min", "0.2", ""));
+        assertTrue(complete(sender, "set", "min", "0.").contains("0.2"));
+        for (String bound : List.of("min", "max")) {
+            for (String value : complete(sender, "set", bound, "")) {
+                live.candidate(bound, Double.parseDouble(value));
+            }
+        }
+        live.setBound("max", 0.8);
+        assertTrue(complete(sender, "set", "max", "0.").contains("0.8"));
+        assertEquals(List.of(), complete(sender, "set", "min", "1"));
+    }
+
+    @Test
+    void saveFailureIsReportedWithoutChangingActiveSettings() {
+        LiveHeightSettings failing = new LiveHeightSettings(live.get(), settings -> {
+            throw new IOException("test save failure");
+        });
+        new HeightsCommand(failing, Logger.getAnonymousLogger()).onCommand(
+                sender(true), null, "heights", new String[] {"set", "min", "0.2"});
+        assertTrue(messages.getLast().contains("Could not save"));
+        assertEquals(0.4, failing.get().minimum());
+    }
+
+    private List<String> complete(CommandSender sender, String... args) {
+        return command.onTabComplete(sender, null, "heights", args);
+    }
+
+    private CommandSender sender(boolean permitted) {
+        return (CommandSender) Proxy.newProxyInstance(CommandSender.class.getClassLoader(),
+                new Class<?>[] {CommandSender.class}, (proxy, method, args) -> {
+                    if (method.getName().equals("hasPermission")) {
+                        assertEquals("spigotheights.admin", args[0]);
+                        return permitted;
+                    }
+                    if (method.getName().equals("sendMessage") && args[0] instanceof String text) {
+                        messages.add(text);
+                        return null;
+                    }
+                    throw new UnsupportedOperationException(method.getName());
+                });
+    }
+}

src/test/java/games/dmg/spigotheights/LiveHeightSettingsTest.java

@@ -0,0 +1,50 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class LiveHeightSettingsTest {
+    private static final HeightSettings DEFAULTS = new HeightSettings(0.4, 2.0, 0.1, 0.5, 1.5, 20);
+
+    @Test
+    void savesBeforePublishingAndGameplayReadsNewBounds() throws Exception {
+        List<HeightSettings> saved = new ArrayList<>();
+        LiveHeightSettings live = new LiveHeightSettings(DEFAULTS, saved::add);
+        live.setBound("min", 0.2);
+        live.setBound("max", 3.0);
+        assertEquals(2, saved.size());
+        assertSame(saved.getLast(), live.get());
+        assertEquals(0.2, HeightMath.randomScale(live.get(), bound -> 0));
+        assertEquals(3.0, HeightMath.grow(3.0, live.get()));
+        assertEquals(0.2, HeightMath.safeStoredScale(0.1, live.get()));
+        assertEquals(1.0, HeightMath.safeStoredScale(1.0, live.get()));
+        assertEquals(0.1, live.get().adjustmentStep());
+        assertEquals(0.5, live.get().launcherThreshold());
+    }
+
+    @Test
+    void invalidChangesAndSaveFailuresDoNotPublish() {
+        List<HeightSettings> saved = new ArrayList<>();
+        LiveHeightSettings live = new LiveHeightSettings(DEFAULTS, saved::add);
+        for (double value : new double[] {Double.NaN, Double.POSITIVE_INFINITY, -1, 0, 0.01, 0.6, 3}) {
+            assertThrows(IllegalArgumentException.class, () -> live.setBound("min", value));
+        }
+        for (double value : new double[] {0.3, 0.45, 17, Double.NEGATIVE_INFINITY}) {
+            assertThrows(IllegalArgumentException.class, () -> live.setBound("max", value));
+        }
+        assertThrows(IllegalArgumentException.class, () -> live.setBound("speed", 1));
+        assertEquals(List.of(), saved);
+        assertSame(DEFAULTS, live.get());
+        LiveHeightSettings failing = new LiveHeightSettings(DEFAULTS, settings -> {
+            throw new IOException("disk full");
+        });
+        assertThrows(IOException.class, () -> failing.setBound("min", 0.2));
+        assertSame(DEFAULTS, failing.get());
+    }
+}

src/test/java/games/dmg/spigotheights/SettingsFileStoreTest.java

@@ -0,0 +1,47 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.bukkit.configuration.file.YamlConfiguration;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class SettingsFileStoreTest {
+    @TempDir
+    Path directory;
+
+    @Test
+    void savedBoundsSurviveReloadAndPreserveOtherConfiguration() throws Exception {
+        Path config = directory.resolve("config.yml");
+        try (var defaults = getClass().getResourceAsStream("/config.yml")) {
+            Files.copy(defaults, config);
+        }
+        Files.writeString(config, Files.readString(config) + "\nfuture-setting: retained\n");
+        HeightSettings initial = SpigotHeightsPlugin.loadSettings(YamlConfiguration.loadConfiguration(config.toFile()));
+        LiveHeightSettings live = new LiveHeightSettings(initial, new SettingsFileStore(config)::save);
+        live.setBound("min", 0.2);
+        live.setBound("max", 3.0);
+        YamlConfiguration reloaded = YamlConfiguration.loadConfiguration(config.toFile());
+        assertEquals(live.get(), SpigotHeightsPlugin.loadSettings(reloaded));
+        assertEquals("retained", reloaded.getString("future-setting"));
+        try (var files = Files.list(directory)) {
+            assertEquals(1, files.count());
+        }
+    }
+
+    @Test
+    void malformedConfigurationIsNotOverwrittenOrActivated() throws Exception {
+        Path config = directory.resolve("config.yml");
+        String malformed = "height: [unterminated";
+        Files.writeString(config, malformed);
+        HeightSettings initial = new HeightSettings(0.4, 2.0, 0.1, 0.5, 1.5, 20);
+        LiveHeightSettings live = new LiveHeightSettings(initial, new SettingsFileStore(config)::save);
+        assertThrows(IOException.class, () -> live.setBound("min", 0.2));
+        assertEquals(initial, live.get());
+        assertEquals(malformed, Files.readString(config));
+    }
+}