feat(heights): carry consenting players with native dismounts

AGENTS.md

@@ -1,18 +1,9 @@
-# Spigot Heights Agent Guide
+# spigot-heights agent entrypoint
 
-## Canonical design
+The canonical stories, engineering guidance, and **all process documents** are in the private [SoMC OKF wiki](https://git.garvis.dev/dmg/somc-okf/src/branch/main/index.md).
 
-- `design/` is the canonical OKF v0.1 knowledge bundle.
-- Read relevant user stories before implementation and keep acceptance criteria and `design/log.md` synchronized with verified behavior.
+Before work, read the sibling `../somc-okf/index.md`, `../somc-okf/processes/index.md`, `../somc-okf/projects/spigot-heights/index.md`, `engineering.md` in that project section, and relevant `../somc-okf/user-stories/spigot-heights/` stories. Also follow the parent workspace `AGENTS.md` when present.
 
-## Engineering
+For standalone checkouts, start at the [project page](https://git.garvis.dev/dmg/somc-okf/src/branch/main/projects/spigot-heights/index.md) and [shared process](https://git.garvis.dev/dmg/somc-okf/src/branch/main/processes/development.md). Obtain wiki access before feature work; do not recreate a local knowledge bundle. Source builds do not require private wiki access.
 
-- Target Java 25 and Purpur `26.2.build.2618-stable`.
-- Use Gradle Kotlin DSL and JUnit 5.
-- Prefer small, server-independent domain classes with Bukkit adapters at the boundary.
-- Develop test-first where practical and verify with `./gradlew clean check jar`.
-- Treat custom item identity as persistent metadata; never trust display names.
-- Validate all configuration before enabling gameplay behavior.
-- Persist player data by UUID and use atomic replacement where supported.
-- Keep event handlers on the server thread and avoid unnecessary work on player movement.
-- Use conventional commits in the form `type(scope): description`.
+Development follows [Development cycle](https://git.garvis.dev/dmg/somc-okf/src/branch/main/runbooks/development-cycle.md): approved stories, failing tests, passing implementation, verification, then source/wiki commit and push. GitOps updates are committed locally **without pushing**; only [Do release](https://git.garvis.dev/dmg/somc-okf/src/branch/main/runbooks/do-release.md) authorizes a reviewed GitOps push.

README.md

@@ -2,7 +2,7 @@
 
 A Purpur 26.2 plugin adding craftable player-scaling potions and dispenser launch tubes for tiny players.
 
-Approved behavior is specified in the [OKF design bundle](design/index.md).
+Approved behavior is specified in the [SoMC OKF wiki](https://git.garvis.dev/dmg/somc-okf/src/branch/main/projects/spigot-heights/index.md).
 
 ## Requirements
 
@@ -41,7 +41,43 @@ Amethyst Shard | Potion of Shifting Stature | Amethyst Shard
 Gold Ingot     | Sugar                      | Gold Ingot
 ```
 
-Produces one Potion of Restoration. Drinking it restores scale to exactly `1.0` (normal size), even outside configured limits. This size is saved across reconnects, respawns, and server restarts. Other saved scales are still clamped to the configured range.
+Produces one Potion of Restoration. Drinking it restores scale to exactly `1.0` (normal size), even outside configured limits. This size is saved across reconnects, respawns, and server restarts. Other permanent saved scales are still clamped to the configured range.
+
+### Temporary splash and lingering variants
+
+Brew any of the four authenticated stature potions with **gunpowder** to make its splash variant; brew that with **dragon's breath** to make its lingering variant. Brewing preserves the stature kind, not arbitrary cosmetic renames/lore. Ordinary potions and cancelled brewing/application events are not overridden. Renaming an ordinary item cannot turn it into a stature potion.
+
+Each splash/cloud applies once per player, without recipient opt-in. The first application saves the player's original base scale. Further applications operate on the temporary scale and reset expiry to **five minutes after the latest application**, including a valid application already at a stature bound. Growth/shrinking respect the current limits; throwable Restoration sets temporary scale to exactly `1.0`.
+
+Example: `1.0 → 0.8`, then `0.8 → 0.6` four minutes later, returns to `1.0` five minutes after the second application. Expiry restores the **exact original baseline**, even if administrator limits changed meanwhile. Offline time counts. Baseline, expiry, and application receipts are persisted; a pending restoration survives disconnect during persistence and is acknowledged only after live application. After that sequence is cleared, ordinary later joins/respawns use the usual limit policy.
+
+Drinking a permanent stature potion ends the temporary sequence, using the current temporary scale (or restored baseline if already expired). Administrator height changes also end the sequence. File writes are serialized off the server tick thread; failed saves do not apply an unsaved change. Disable waits for the active writer and drains its result before returning. Do not forcibly kill the server while it is saving.
+
+Heights tracks only its loaded clouds and checks them every five ticks, dispatching `AreaEffectCloudApplyEvent` and honoring cancellation and recipient filtering. This supports effectless stature clouds without adding a vanilla status effect. Online expiry is checked every second. Durable receipts survive cloud unload and are retired on observed permanent entity removal; abrupt process termination can leave harmless orphan receipts.
+
+**Verification:** automated domain and Bukkit-boundary tests cover this implementation. Actual brewing, cloud delivery, client appearance, and logout/restart gameplay on Purpur 26.2 build 2618 still require manual acceptance checks.
+
+## Consensual carrying (US-010; live acceptance pending)
+
+Sneak-right-click another player with your main hand to request a ride or pickup. The larger player is always the carrier, regardless of who asks. The other player has **30 seconds** to explicitly accept:
+
+```text
+/heights carry accept
+/heights carry decline
+/heights carry stop
+```
+
+These commands require **no administrator permission**; settings and player-height commands still require `spigotheights.admin`. Console cannot carry players. One outstanding request per participant prevents replacement/ambiguous consent. Either participant can withdraw a pending request with `stop`; `decline` rejects an incoming request. Requests and carry tracking are not persisted.
+
+Both players must be available and within **4 blocks**, in the same world, when requesting and accepting. Their **effective** scale difference must be at least **three current adjustment steps** (normally `0.3`), including other plugins' attribute modifiers. Neither may already have a vehicle or passengers. Heights permits only one rider per carrier, and blocks additional/nested mounts involving an active pair.
+
+Either player can stop with **normal Minecraft dismounting**. Heights calls the rider's native `leaveVehicle()` and allows ordinary sneak-dismounts, leaving placement, falling, damage, and environmental hazards to Minecraft. There is no safe-ground requirement or search, rescue teleport, saved-position/spawn fallback, motion/fall-distance reset, invulnerability, or recovery system. Getting off above a drop is a gameplay risk.
+
+Eligibility is rechecked every five ticks, including temporary potion application/expiry, administrator edits and external scale modifiers. Death, disconnect, plugin disable and loss of eligibility attempt native cleanup. For observed teleport events, Heights detaches the pair and lets the original teleport continue, without replaying or redirecting it. Native carrier teleports that refuse passengers before emitting an event may still require `/heights carry stop` first.
+
+Server/plugin cancellation remains authoritative: a refused dismount leaves accurate tracking and is reported, not bypassed or called successful. A cancelled voluntary stop can be retried by either player; automatic eligibility cleanup continues checking and reports refusal once per ride rather than spamming. Lifecycle/disable refusals are logged. Native dismount events are reconciled after dispatch so a later cancellation is honored. An unrelated vehicle is never ejected during stale-pair cleanup.
+
+**Verification:** automated domain and constructed Bukkit-event tests are not live-server evidence. Purpur 26.2 build 2618 still needs checks for scaled rider positioning and movement, ordinary dismount placement/falling, cancellation interoperability, both-role death/disconnect, portal/cross-world teleports, plugin disable and eligibility changes. No throwing or added launch force, player items, storage, or changes to throwable-potion opt-in behavior are included.
 
 ## Tiny-player launchers
 
@@ -64,6 +100,32 @@ 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
+/heights player Steve
+/heights player Steve 0.5
+```
+
+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`. Processing an expired temporary sequence is another exception: its exact baseline is restored before ordinary later joins/respawns follow the new limits. The settings commands only change min/max; edit other settings in the configuration file and restart the server.
+
+### Player height
+
+`/heights player <name>` reports an online player's scale (`1.0` = normal size). If another plugin adds scale modifiers, both the base scale and effective scale are shown.
+
+`/heights player <name> <scale>` sets that player's base scale by UUID after an asynchronous durable save and ends any temporary sequence. Values must be finite and within current min/max limits, except `1.0` is always allowed. Saved scales follow the usual limits on reconnect and respawn if configuration changes later. A failed save leaves the player's height unchanged.
+
+Player names must match an online player exactly (case-insensitive); partial names and offline players are rejected. Tab completion suggests online names and valid example sizes. Operators, console, and senders with `spigotheights.admin` may view or set heights, including their own.
+
 ## Build
 
 ```bash

design/index.md

@@ -1,15 +0,0 @@
----
-type: Index
-title: Spigot Heights Design
-description: Entry point for the Spigot Heights OKF knowledge bundle.
-okf_version: "0.1"
----
-
-# Spigot Heights Design
-
-This bundle documents craftable player-scaling potions, configurable stature limits, tiny-player dispenser launchers, persistence, and delivery requirements.
-
-## Explore
-
-- [User stories](user-stories/index.md)
-- [Design log](log.md)

design/log.md

@@ -1,40 +0,0 @@
----
-type: Log
-title: Spigot Heights Design Log
-description: Chronological record of material decisions affecting Spigot Heights.
----
-
-# Spigot Heights Design Log
-
-## 2026-09-06T23:41:16Z — Restoration completed
-
-- Added the white Potion of Restoration with persistent identity and the approved Sugar upgrade recipe.
-- Consumption restores exact scale `1.0` through the existing report/save path; saved `1.0` bypasses configured-range clamping on join and respawn.
-- Verified `./gradlew clean check jar`: all 17 tests passed, including restoration, persistence reload, range exceptions, recipe shape, identity, and existing potion regression coverage.
-- Inspected Bukkit recipe/metadata and event wiring; live-server gameplay verification remains unperformed. Updated the README and completed US-006 and the related US-004 change.
-
-## 2026-09-06T23:37:19Z — Restoration approved and implementation started
-
-- Approved [US-006](user-stories/us-006-restore-default-stature.md): a Sugar-based upgrade of Shifting Stature restores exact scale `1.0`.
-- Approved an exception to saved-scale clamping in [US-004](user-stories/us-004-configure-and-persist.md) so restoration survives reconnects and respawns even outside configured limits.
-
-## 2026-09-04 — Initial design approved
-
-- Player scale defaults to a configurable range of `0.4` through `2.0`.
-- A moderate recipe creates a random stature potion; more expensive upgrades create targeted growth and diminution potions.
-- Random stature is selected uniformly in configurable `0.1` increments.
-- Players strictly below scale `0.5` can be launched through a dispenser fed by the hopper beneath them.
-- Launcher speed defaults to 1.5 blocks per tick with a 20-tick cooldown and safe-exit checks.
-- The project follows the neighboring Spigot Base Java 25, Purpur, Gradle, OKF, CI, and release conventions.
-
-## 2026-09-04 — Implementation started
-
-- Approved implementation began with user stories, tests, and the Gradle/Purpur foundation.
-
-## 2026-09-04 — Initial release scope completed
-
-- Implemented authenticated random, growth, and diminution potions with approved recipes and durable UUID-keyed player scale.
-- Added validated stature and launcher configuration with safe clamping to Minecraft's scale range.
-- Implemented cooldown-protected hopper-to-dispenser launch tubes for tiny players with six-axis launch support and empty-exit checks.
-- Added the Java 25 Purpur build, automated tests, Gitea CI and semantic-release workflows, README, and project-specific agent guidance.
-- Verified the implementation with `./gradlew clean check jar` and created the public `dmg/spigot-heights` Gitea repository.

design/user-stories/index.md

@@ -1,14 +0,0 @@
----
-type: Index
-title: Spigot Heights User Stories
-description: Catalog of user stories for the Spigot Heights plugin.
----
-
-# Spigot Heights User Stories
-
-1. [US-001: Drink a Potion of Shifting Stature](us-001-drink-shifting-stature-potion.md)
-2. [US-002: Make precise stature adjustments](us-002-adjust-stature.md)
-3. [US-003: Launch tiny players through dispensers](us-003-launch-tiny-players.md)
-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)

design/user-stories/us-001-drink-shifting-stature-potion.md

@@ -1,25 +0,0 @@
----
-type: User Story
-title: "US-001: Drink a Potion of Shifting Stature"
-description: Let players craft and drink a potion that gives them a random configured scale.
-status: done
----
-
-# US-001: Drink a Potion of Shifting Stature
-
-As a **player**, I want to drink a craftable potion that changes my stature unpredictably so that player size becomes a fun survival mechanic.
-
-## Acceptance criteria
-
-- [x] The distinct potion is authenticated with persistent item metadata rather than its display name alone.
-- [x] Its shaped recipe is `ACA/AWA/ACA`, where `A` is Amethyst Shard, `C` is Chorus Fruit, and `W` is an Awkward Potion.
-- [x] Drinking it consumes one potion, leaves normal bottle handling intact, and selects a scale from the configured inclusive range.
-- [x] Outcomes are uniformly selected in configured adjustment-step increments, including both endpoints when aligned.
-- [x] The resulting Minecraft scale attribute is applied and reported to the player.
-- [x] The resulting scale persists across logout, restart, world change, and death.
-- [x] Automated tests cover bounds, endpoint reachability, and recipe identity.
-
-## Related
-
-- [US-002: Make precise stature adjustments](us-002-adjust-stature.md)
-- [US-004: Configure and persist stature behavior](us-004-configure-and-persist.md)

design/user-stories/us-002-adjust-stature.md

@@ -1,24 +0,0 @@
----
-type: User Story
-title: "US-002: Make precise stature adjustments"
-description: Let players craft upgraded potions that increase or decrease scale by one configured step.
-status: done
----
-
-# US-002: Make precise stature adjustments
-
-As a **player**, I want more expensive growth and diminution potions so that I can adjust my stature predictably.
-
-## Acceptance criteria
-
-- [x] The Potion of Growth uses `GAG/ASA/GRG`, where `G` is Gold Ingot, `A` is Amethyst Shard, `S` is an authenticated Potion of Shifting Stature, and `R` is Rabbit's Foot.
-- [x] The Potion of Diminution uses `GAG/ASA/GFG`, where `F` is Fermented Spider Eye.
-- [x] Each resulting potion has distinct persistent metadata.
-- [x] Growth adds one configured adjustment step and clamps at the maximum.
-- [x] Diminution subtracts one configured adjustment step and clamps at the minimum.
-- [x] Adjusted scales are reported and persisted under the same rules as random stature.
-- [x] Automated tests cover adjustment, clamping, and potion identity.
-
-## Related
-
-- [US-001: Drink a Potion of Shifting Stature](us-001-drink-shifting-stature-potion.md)

design/user-stories/us-003-launch-tiny-players.md

@@ -1,25 +0,0 @@
----
-type: User Story
-title: "US-003: Launch tiny players through dispensers"
-description: Launch sufficiently small players from a dispenser connected to the hopper beneath them.
-status: done
----
-
-# US-003: Launch tiny players through dispensers
-
-As a **tiny player**, I want connected hoppers and dispensers to act as launch tubes so that my stature enables playful transport systems.
-
-## Acceptance criteria
-
-- [x] A player strictly below the configured threshold triggers when walking onto a hopper whose output points into a dispenser.
-- [x] No redstone signal is required.
-- [x] The player moves to a safe centered position immediately in front of the dispenser and receives velocity in its facing direction.
-- [x] Velocity magnitude and cooldown are configurable and default to 1.5 blocks per tick and 20 ticks.
-- [x] Obstructed or unsafe exits abort without moving the player.
-- [x] Players at or above the threshold are not launched.
-- [x] Cooldown prevents immediate repeated or cyclic launching.
-- [x] Automated tests cover threshold boundaries, orientations, cooldown, and obstruction policy.
-
-## Related
-
-- [US-004: Configure and persist stature behavior](us-004-configure-and-persist.md)

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

@@ -1,26 +0,0 @@
----
-type: User Story
-title: "US-004: Configure and persist stature behavior"
-description: Give operators validated settings and durable UUID-keyed player scales.
-status: done
----
-
-# US-004: Configure and persist stature behavior
-
-As a **server operator**, I want validated stature and launcher settings with durable state so that behavior remains safe and predictable.
-
-## Acceptance criteria
-
-- [x] Defaults are minimum `0.4`, maximum `2.0`, adjustment step `0.1`, launcher threshold `0.5`, speed `1.5`, and cooldown `20` ticks.
-- [x] Configuration requires finite positive values, minimum no greater than maximum, and a launcher threshold within the supported scale range.
-- [x] Invalid startup configuration disables the plugin with a clear error.
-- [x] Player scales are stored by UUID using atomic file replacement where supported.
-- [x] Updating known state preserves unknown forward-compatible YAML fields.
-- [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.
-
-## Related
-
-- [User-story catalog](index.md)
-- [US-006: Restore default stature](us-006-restore-default-stature.md)

design/user-stories/us-005-build-and-release.md

@@ -1,24 +0,0 @@
----
-type: User Story
-title: "US-005: Build and release the plugin"
-description: Give maintainers repeatable Purpur builds, automated verification, and versioned Gitea releases.
-status: done
----
-
-# US-005: Build and release the plugin
-
-As a **plugin maintainer**, I want automated builds and releases modeled on Spigot Base so that tested artifacts can be distributed consistently.
-
-## Acceptance criteria
-
-- [x] Gradle compiles against Purpur API `26.2.build.2618-stable` using Java 25.
-- [x] Compiler lint warnings fail the build and JUnit 5 tests run during `check`.
-- [x] Gitea Actions verifies pushes and pull requests and stores a development JAR.
-- [x] Pull requests validate conventional commits.
-- [x] Main-branch conventional commits drive semantic releases and attach versioned JARs to Gitea releases.
-- [x] The README documents requirements, recipes, configuration, building, and releases.
-- [x] `./gradlew clean check jar` succeeds.
-
-## Related
-
-- [User-story catalog](index.md)

design/user-stories/us-006-restore-default-stature.md

@@ -1,28 +0,0 @@
----
-type: User Story
-title: "US-006: Restore default stature"
-description: Let players craft a potion that permanently restores their scale to 1.0.
-status: done
----
-
-# US-006: Restore default stature
-
-As a **player**, I want a Potion of Restoration so that I can return to normal size.
-
-## Acceptance criteria
-
-- [x] Drinking the potion sets scale to exactly `1.0`, regardless of configured limits.
-- [x] The potion uses distinct persistent metadata rather than its display name for identity.
-- [x] The new scale is reported and saved by UUID, and retained across reconnects and respawns.
-- [x] The recipe is `GAG/ASA/GUG`, where `G` is Gold Ingot, `A` is Amethyst Shard, `S` is an authenticated Potion of Shifting Stature, and `U` is Sugar.
-- [x] Automated tests cover restoration, saved-scale handling, recipe shape, and distinct identity; the README documents the recipe and behavior.
-
-## Verification
-
-- `./gradlew clean check jar` passed all 17 tests.
-- Automated coverage checks scale calculation, storage reload, range exceptions, recipe shape, and enum identity. Code inspection confirms metadata authentication, ingredient registration, and the shared consumption/join/respawn adapters; no live-server gameplay test was performed.
-
-## Related
-
-- [US-002: Make precise stature adjustments](us-002-adjust-stature.md)
-- [US-004: Configure and persist stature behavior](us-004-configure-and-persist.md)

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

@@ -0,0 +1,176 @@
+package games.dmg.spigotheights;
+
+import java.util.UUID;
+import java.util.function.*;
+import java.util.logging.Logger;
+import org.bukkit.GameMode;
+import org.bukkit.Server;
+import org.bukkit.attribute.Attribute;
+import org.bukkit.attribute.AttributeInstance;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerInteractAtEntityEvent;
+import org.bukkit.event.player.PlayerInteractEntityEvent;
+import org.bukkit.inventory.EquipmentSlot;
+
+/** Bukkit boundary for the consent state machine. All methods run on the server thread. */
+public final class BukkitCarry implements Listener, CarryService.Port, AutoCloseable {
+    private final Function<UUID, Player> players;
+    private final Consumer<Runnable> nextTick;
+    private final Logger logger;
+    private final ToDoubleFunction<Player> scales;
+    private final CarryService service;
+    private final java.util.Set<UUID> dismounting = new java.util.HashSet<>();
+    private final java.util.Set<UUID> queuedStops = new java.util.HashSet<>();
+    private UUID mountingCarrier, mountingRider;
+    private boolean closed;
+
+    public BukkitCarry(Server server, Supplier<HeightSettings> settings, Consumer<Runnable> nextTick, Logger logger) {
+        this(server::getPlayer, settings, nextTick, logger, player -> {
+            AttributeInstance attribute = player.getAttribute(Attribute.SCALE);
+            return attribute == null ? Double.NaN : attribute.getValue();
+        }, () -> System.nanoTime() / 1_000_000);
+    }
+    BukkitCarry(Function<UUID, Player> players, Supplier<HeightSettings> settings,
+            Consumer<Runnable> nextTick, Logger logger, ToDoubleFunction<Player> scales, LongSupplier clock) {
+        this.players = players; this.nextTick = nextTick; this.logger = logger;
+        this.scales = scales;
+        service = new CarryService(this, () -> settings.get().adjustmentStep(), clock);
+    }
+
+    @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
+    public void interact(PlayerInteractEntityEvent event) {
+        if (event.isCancelled() || event instanceof PlayerInteractAtEntityEvent
+                || event.getHand() != EquipmentSlot.HAND || !event.getPlayer().isSneaking()
+                || !(event.getRightClicked() instanceof Player target)) { return; }
+        event.setCancelled(true);
+        Player sender = event.getPlayer();
+        String result = service.request(sender.getUniqueId(), target.getUniqueId());
+        sender.sendMessage(result);
+        if (result.equals("Carry request sent.")) {
+            target.sendMessage(sender.getName() + (scales.applyAsDouble(sender) > scales.applyAsDouble(target)
+                    ? " wants to carry you." : " wants to ride with you."));
+        }
+    }
+    public void command(Player player, String action) {
+        UUID id = player.getUniqueId();
+        player.sendMessage(switch (action) {
+            case "accept" -> service.accept(id);
+            case "decline" -> service.decline(id);
+            case "stop" -> service.stop(id);
+            default -> "Usage: /heights carry accept|decline|stop";
+        });
+    }
+    @Override public CarryService.State state(UUID id) {
+        Player player = players.apply(id);
+        if (player == null) { return null; }
+        return new CarryService.State(scales.applyAsDouble(player),
+                player.isOnline() && player.isValid() && !player.isDead() && !player.isSleeping()
+                        && player.getGameMode() != GameMode.SPECTATOR,
+                !player.isInsideVehicle() && player.getPassengers().isEmpty());
+    }
+    @Override public boolean nearby(UUID first, UUID second) {
+        Player a = players.apply(first), b = players.apply(second);
+        return a != null && b != null && a.getWorld().getUID().equals(b.getWorld().getUID())
+                && a.getLocation().toVector().distanceSquared(b.getLocation().toVector()) <= 16;
+    }
+    @Override public boolean mount(UUID carrier, UUID rider) {
+        Player a = players.apply(carrier), b = players.apply(rider);
+        if (a == null || b == null) { return false; }
+        mountingCarrier = carrier; mountingRider = rider;
+        try { return a.addPassenger(b) && attached(carrier, rider); }
+        finally { mountingCarrier = null; mountingRider = null; }
+    }
+    @Override public boolean linked(UUID carrier, UUID rider) {
+        Player b = players.apply(rider);
+        return b != null && b.getVehicle() != null && b.getVehicle().getUniqueId().equals(carrier);
+    }
+    @Override public boolean attached(UUID carrier, UUID rider) {
+        Player a = players.apply(carrier), b = players.apply(rider);
+        return a != null && b != null && b.getVehicle() != null && b.getVehicle().getUniqueId().equals(carrier)
+                && !a.isInsideVehicle() && b.getPassengers().isEmpty() && a.getPassengers().size() == 1
+                && a.getPassengers().getFirst().getUniqueId().equals(rider)
+                && a.getWorld().getUID().equals(b.getWorld().getUID());
+    }
+    @Override public boolean dismount(UUID carrier, UUID rider) {
+        Player b = players.apply(rider);
+        if (b == null) {
+            Player a = players.apply(carrier);
+            if (a != null) {
+                b = a.getPassengers().stream().filter(entity -> entity.getUniqueId().equals(rider))
+                        .filter(Player.class::isInstance).map(Player.class::cast).findFirst().orElse(null);
+            }
+        }
+        if (b == null || b.getVehicle() == null || !b.getVehicle().getUniqueId().equals(carrier)) {
+            return true; // Already detached; never disturb an unrelated vehicle.
+        }
+        if (!dismounting.add(rider)) { return false; }
+        try {
+            b.leaveVehicle();
+        } finally {
+            dismounting.remove(rider);
+        }
+        // Native API return values do not reliably reflect cancellation. Inspect the relationship.
+        return b.getVehicle() == null || !b.getVehicle().getUniqueId().equals(carrier);
+    }
+    @Override public void message(UUID id, String message) {
+        Player player = players.apply(id);
+        if (player != null && player.isOnline()) { player.sendMessage(message); }
+    }
+    @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
+    public void mountEvent(org.bukkit.event.entity.EntityMountEvent event) {
+        UUID rider = event.getEntity().getUniqueId(), carrier = event.getMount().getUniqueId();
+        if (rider.equals(mountingRider) && carrier.equals(mountingCarrier)) { return; }
+        if (service.involved(rider) || service.involved(carrier)
+                || rider.equals(mountingCarrier) || carrier.equals(mountingRider)
+                || rider.equals(mountingRider) || carrier.equals(mountingCarrier)) { event.setCancelled(true); }
+    }
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void dismountEvent(org.bukkit.event.entity.EntityDismountEvent event) {
+        UUID id = event.getEntity().getUniqueId();
+        if (event.isCancelled() || dismounting.contains(id) || !service.involved(id)
+                || closed || !queuedStops.add(id)) { return; }
+        // The event precedes native detachment. Reconcile actual attachment next tick;
+        // never cancel sneak-dismount or force a second dismount if another listener cancels.
+        nextTick.accept(() -> {
+            queuedStops.remove(id);
+            if (!closed && !event.isCancelled()) { service.tick(); }
+        });
+    }
+    @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
+    public void teleportEvent(org.bukkit.event.player.PlayerTeleportEvent event) {
+        if (event.isCancelled()) { return; }
+        Player player = event.getPlayer();
+        UUID id = player.getUniqueId();
+        // No rescue/replay teleport: detach through the native API, then allow the original.
+        // If another plugin refuses detachment, do not move an attached pair behind its back.
+        if (!service.cleanup(id)) {
+            event.setCancelled(true);
+            player.sendMessage("The server refused the dismount; stop carrying before teleporting.");
+        }
+    }
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void quit(org.bukkit.event.player.PlayerQuitEvent event) {
+        UUID id = event.getPlayer().getUniqueId();
+        if (!service.cleanup(id)) { reportUnresolved(id, "disconnect"); }
+    }
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void death(org.bukkit.event.entity.PlayerDeathEvent event) {
+        if (event.isCancelled()) { return; }
+        UUID id = event.getEntity().getUniqueId();
+        if (!service.cleanup(id)) { reportUnresolved(id, "death"); }
+    }
+    private void reportUnresolved(UUID id, String cause) {
+        logger.severe("Heights " + cause + ": carry involving " + id
+                + " remains attached because the server refused native dismounting; no cancellation was bypassed.");
+    }
+    public void tick() { if (!closed) { service.tick(); } }
+    @Override public void close() {
+        closed = true;
+        int unresolved = service.close();
+        if (unresolved != 0) { logger.severe("Heights disable: " + unresolved
+                + " native dismount(s) were refused by the server; no cancellation was bypassed."); }
+    }
+}

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

@@ -0,0 +1,34 @@
+package games.dmg.spigotheights;
+
+import java.util.List;
+import org.bukkit.Server;
+import org.bukkit.attribute.Attribute;
+import org.bukkit.attribute.AttributeInstance;
+import org.bukkit.entity.Player;
+
+/** Bukkit boundary for exact online-player lookup; used only on the server thread. */
+public final class BukkitPlayerHeights {
+    private final Server server;
+
+    public BukkitPlayerHeights(Server server) {
+        this.server = server;
+    }
+
+    public PlayerHeights.Target find(String name) {
+        Player player = server.getPlayerExact(name);
+        if (player == null) {
+            return null;
+        }
+        AttributeInstance scale = player.getAttribute(Attribute.SCALE);
+        if (scale == null) {
+            throw new IllegalArgumentException("Player " + player.getName() + " has no scale attribute.");
+        }
+        return new PlayerHeights.Target(player.getUniqueId(), player.getName(), scale.getBaseValue(),
+                scale.getValue(), scale::setBaseValue);
+    }
+
+    public List<String> names() {
+        return server.getOnlinePlayers().stream().map(Player::getName)
+                .sorted(String.CASE_INSENSITIVE_ORDER).toList();
+    }
+}

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

@@ -0,0 +1,211 @@
+package games.dmg.spigotheights;
+
+import java.time.Instant;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import org.bukkit.attribute.Attribute;
+import org.bukkit.attribute.AttributeInstance;
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.java.JavaPlugin;
+
+/** Captures Bukkit state on the tick thread; all stature file writes run on one worker. */
+public final class BukkitStatureService implements AutoCloseable {
+    private final JavaPlugin plugin;
+    private final Supplier<HeightSettings> settings;
+    private final HeightStore store;
+    private final TemporaryStature stature;
+    private final ExecutorService worker = Executors.newSingleThreadExecutor(Thread.ofPlatform()
+            .name("heights-state").factory());
+    private final StatureQueue queue;
+    private final CompletionMailbox completions;
+    private final Set<UUID> expiring = new HashSet<>();
+
+    public BukkitStatureService(JavaPlugin plugin, Supplier<HeightSettings> settings, HeightStore store) {
+        this.plugin = plugin;
+        this.settings = settings;
+        this.store = store;
+        this.stature = new TemporaryStature(store);
+        completions = new CompletionMailbox(task -> {
+            if (plugin.isEnabled()) {
+                try {
+                    plugin.getServer().getScheduler().runTask(plugin, task);
+                } catch (org.bukkit.plugin.IllegalPluginAccessException ignored) {
+                    // Disable raced with a completed, already durable write. Login will resume it.
+                }
+            }
+        });
+        queue = new StatureQueue(worker, completions);
+    }
+
+    public void temporary(UUID source, Player player, StaturePotion kind, Consumer<Boolean> completed) {
+        change(player, kind, source, completed);
+    }
+
+    public void drink(Player player, StaturePotion kind) {
+        change(player, kind, null, success -> {});
+    }
+
+    private void change(Player player, StaturePotion kind, UUID source, Consumer<Boolean> completed) {
+        UUID id = player.getUniqueId();
+        queue.submit(() -> {
+            Player currentPlayer = requireOnline(id);
+            double current = scale(currentPlayer);
+            HeightSettings limits = settings.get();
+            Instant now = Instant.now();
+            return () -> {
+                // A duplicate returns null; do not unbox it through a mixed Double/double ternary.
+                if (source != null) {
+                    return stature.applyOnce(id, source, current, kind, limits, now,
+                            bound -> ThreadLocalRandom.current().nextInt(bound));
+                }
+                return stature.drink(id, current, kind, limits, now,
+                        bound -> ThreadLocalRandom.current().nextInt(bound));
+            };
+        }, (result, error) -> {
+            if (error == null) {
+                if (result != null) {
+                    applyOnline(id, result);
+                }
+                completed.accept(true);
+            } else {
+                report(id, error);
+                completed.accept(false);
+            }
+        });
+    }
+
+    public void resume(Player player) {
+        UUID id = player.getUniqueId();
+        queue.submit(() -> {
+            requireOnline(id);
+            HeightSettings limits = settings.get();
+            Instant now = Instant.now();
+            return () -> stature.resume(id, limits, now);
+        }, (result, error) -> {
+            if (error == null) { applyRestoration(id, result); } else { report(id, error); }
+        });
+    }
+
+    /** Called once a second, not on movement; reads immutable cached state only. */
+    public void expireOnline() {
+        Instant now = Instant.now();
+        for (Player player : plugin.getServer().getOnlinePlayers()) {
+            UUID id = player.getUniqueId();
+            HeightStore.Sequence sequence = store.sequence(id);
+            if (player.isDead() || sequence == null || now.isBefore(sequence.expiresAt()) || !expiring.add(id)) {
+                continue;
+            }
+            queue.submit(() -> {
+                HeightSettings limits = settings.get();
+                Instant at = Instant.now();
+                // Recheck at queue execution: a permanent override or a later splash may have won.
+                Callable<Double> work = () -> {
+                    HeightStore.Sequence latest = store.sequence(id);
+                    return latest != null && !at.isBefore(latest.expiresAt()) ? stature.resume(id, limits, at) : null;
+                };
+                return work;
+            }, (result, error) -> {
+                expiring.remove(id);
+                if (error != null) { report(id, error); }
+                else if (result != null) { applyRestoration(id, result); }
+            });
+        }
+    }
+
+    public void retireSource(UUID source) {
+        queue.submit(() -> () -> { store.forgetSource(source); return null; }, (result, error) -> {
+            if (error != null) {
+                plugin.getLogger().warning("Could not retire throwable receipt " + source + ": " + error.getMessage());
+            }
+        });
+    }
+
+    public void set(String name, double value, Consumer<String> reply) {
+        Player target = plugin.getServer().getPlayerExact(name);
+        if (target == null) {
+            reply.accept("No online player named '" + name + "'. Use their full name.");
+            return;
+        }
+        UUID id = target.getUniqueId();
+        queue.submit(() -> {
+            requireOnline(id);
+            HeightSettings limits = settings.get();
+            if (!Double.isFinite(value) || (value != 1.0 && (value < limits.minimum() || value > limits.maximum()))) {
+                throw new IllegalArgumentException("Scale must be finite and within current limits, or exactly 1.0.");
+            }
+            return () -> { store.save(id, value); return value; };
+        }, (result, error) -> {
+            if (error == null) {
+                applyOnline(id, result);
+                reply.accept("Set " + name + "'s base scale to " + result + ". Saved and active.");
+            } else if (error instanceof IllegalArgumentException || error instanceof IllegalStateException) {
+                reply.accept(error.getMessage());
+            } else {
+                report(id, error);
+                reply.accept("Could not save player height. Their height is unchanged; check the server log.");
+            }
+        });
+    }
+
+    private Player requireOnline(UUID id) {
+        Player player = plugin.getServer().getPlayer(id);
+        if (player == null || !player.isOnline() || player.isDead()) {
+            throw new IllegalStateException("Player is no longer available for a stature change.");
+        }
+        return player;
+    }
+
+    private static double scale(Player player) {
+        AttributeInstance attribute = player.getAttribute(Attribute.SCALE);
+        if (attribute == null) {
+            throw new IllegalStateException("Player has no scale attribute.");
+        }
+        return attribute.getBaseValue();
+    }
+
+    private void applyRestoration(UUID id, double value) {
+        HeightStore.Sequence pending = store.sequence(id);
+        if (applyOnline(id, value) && pending != null && !Instant.now().isBefore(pending.expiresAt())) {
+            worker.execute(() -> {
+                try {
+                    stature.acknowledgeRestoration(id, pending);
+                } catch (java.io.IOException exception) {
+                    report(id, exception);
+                }
+            });
+        }
+    }
+
+    private boolean applyOnline(UUID id, double value) {
+        Player player = plugin.getServer().getPlayer(id);
+        if (plugin.isEnabled() && player != null && player.isOnline() && !player.isDead()) {
+            AttributeInstance attribute = player.getAttribute(Attribute.SCALE);
+            if (attribute != null) {
+                attribute.setBaseValue(value);
+                player.sendMessage("Your scale is now " + value + ".");
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private void report(UUID id, Exception error) {
+        plugin.getLogger().warning("Could not update stature for " + id + ": " + error.getMessage());
+    }
+
+    @Override
+    public void close() {
+        queue.close();
+        // Disable is the one blocking lifecycle boundary: never permit an old writer to outlive
+        // this store and overwrite a replacement plugin instance. close() joins even if interrupted.
+        worker.close();
+        completions.drain();
+    }
+}

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

@@ -0,0 +1,16 @@
+package games.dmg.spigotheights;
+
+/** Server-independent carry eligibility, using effective rather than base scale. */
+public final class CarryPolicy {
+    private CarryPolicy() {}
+
+    public static boolean eligible(double carrier, double rider, double step) {
+        if (!Double.isFinite(carrier) || !Double.isFinite(rider) || !Double.isFinite(step)
+                || carrier <= 0 || rider <= 0 || step <= 0 || carrier <= rider) {
+            return false;
+        }
+        double required = 3 * step;
+        double tolerance = 4 * Math.ulp(Math.max(carrier, rider));
+        return Double.isFinite(required) && carrier - rider + tolerance >= required;
+    }
+}

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

@@ -0,0 +1,146 @@
+package games.dmg.spigotheights;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.UUID;
+import java.util.function.DoubleSupplier;
+import java.util.function.LongSupplier;
+
+/** Tick-thread state machine; ports must not perform blocking I/O. */
+public final class CarryService {
+    public record State(double scale, boolean available, boolean free) {}
+    public interface Port {
+        State state(UUID player);
+        boolean nearby(UUID first, UUID second);
+        boolean mount(UUID carrier, UUID rider);
+        boolean attached(UUID carrier, UUID rider);
+        boolean linked(UUID carrier, UUID rider);
+        boolean dismount(UUID carrier, UUID rider);
+        void message(UUID player, String message);
+    }
+    private record Request(UUID sender, UUID recipient, UUID carrier, UUID rider, long sentAt) {}
+    private record Ride(UUID carrier, UUID rider) {}
+    private final Port port;
+    private final DoubleSupplier step;
+    private final LongSupplier clock;
+    private final Map<UUID, Request> requests = new HashMap<>();
+    private final Map<UUID, Ride> rides = new HashMap<>();
+    private final java.util.Set<UUID> reportedRefusals = new java.util.HashSet<>();
+    private boolean closed;
+
+    public CarryService(Port port, DoubleSupplier step, LongSupplier clock) {
+        this.port = port; this.step = step; this.clock = clock;
+    }
+
+    public String request(UUID sender, UUID recipient) {
+        if (closed) { return "Carrying is shutting down."; }
+        expireRequests();
+        if (busy(sender) || busy(recipient)) { return "A player already has a carry request or ride."; }
+        State a = port.state(sender), b = port.state(recipient);
+        if (sender.equals(recipient) || a == null || b == null) { return "Players are unavailable."; }
+        UUID carrier = a.scale() > b.scale() ? sender : recipient;
+        UUID rider = carrier.equals(sender) ? recipient : sender;
+        if (!eligible(carrier, rider, true) || !port.nearby(sender, recipient)) {
+            return "Carry requires nearby, available players differing by at least three adjustment steps.";
+        }
+        Request request = new Request(sender, recipient, carrier, rider, clock.getAsLong());
+        requests.put(recipient, request);
+        port.message(recipient, "Carry request: /heights carry accept or /heights carry decline within 30 seconds.");
+        return "Carry request sent.";
+    }
+
+    public String accept(UUID recipient) {
+        Request request = requests.remove(recipient);
+        if (request == null) { return "No pending request."; }
+        if (clock.getAsLong() - request.sentAt() >= 30_000
+                || involved(request.carrier()) || involved(request.rider())
+                || !eligible(request.carrier(), request.rider(), true)
+                || !port.nearby(request.carrier(), request.rider())) {
+            return "Carry request expired or players are no longer eligible/nearby.";
+        }
+        boolean mounted = port.mount(request.carrier(), request.rider());
+        if (!mounted && !port.linked(request.carrier(), request.rider())) { return "The server refused the ride."; }
+        Ride ride = new Ride(request.carrier(), request.rider());
+        rides.put(ride.carrier(), ride); rides.put(ride.rider(), ride);
+        if (!mounted) {
+            String stopped = stop(ride.rider());
+            String message = "The server produced an invalid ride. " + stopped;
+            if (involved(ride.rider())) { notify(ride, message); }
+            return message;
+        }
+        notify(ride, "Carry started. Either player can /heights carry stop.");
+        return "Carry started.";
+    }
+
+    private boolean eligible(UUID carrier, UUID rider, boolean free) {
+        State a = port.state(carrier), b = port.state(rider);
+        return a != null && b != null && a.available() && b.available()
+                && (!free || (a.free() && b.free()))
+                && CarryPolicy.eligible(a.scale(), b.scale(), step.getAsDouble());
+    }
+
+    private boolean busy(UUID player) {
+        return involved(player) || requests.values().stream()
+                .anyMatch(request -> request.sender().equals(player) || request.recipient().equals(player));
+    }
+
+    private void expireRequests() {
+        requests.values().removeIf(request -> clock.getAsLong() - request.sentAt() >= 30_000);
+    }
+
+    public String decline(UUID recipient) {
+        Request request = requests.remove(recipient);
+        if (request == null) { return "No pending request."; }
+        port.message(request.sender(), "Carry request declined.");
+        return "Carry request declined.";
+    }
+    public String stop(UUID player) {
+        var pending = requests.values().iterator();
+        while (pending.hasNext()) {
+            Request request = pending.next();
+            if (request.sender().equals(player) || request.recipient().equals(player)) {
+                pending.remove();
+                port.message(request.sender().equals(player) ? request.recipient() : request.sender(),
+                        "Carry request cancelled.");
+                return "Carry request cancelled.";
+            }
+        }
+        Ride ride = rides.get(player);
+        if (ride == null) { return "No active ride."; }
+        if (!port.dismount(ride.carrier(), ride.rider())) {
+            return "The server refused the dismount. The ride is still active; retry /heights carry stop.";
+        }
+        rides.remove(ride.carrier()); rides.remove(ride.rider());
+        reportedRefusals.remove(ride.rider());
+        notify(ride, "Carry ended.");
+        return "Carry ended.";
+    }
+    private void notify(Ride ride, String message) {
+        port.message(ride.carrier(), message); port.message(ride.rider(), message);
+    }
+    public void tick() {
+        expireRequests();
+        for (Ride ride : java.util.Set.copyOf(rides.values())) {
+            if (!eligible(ride.carrier(), ride.rider(), false)
+                    || !port.attached(ride.carrier(), ride.rider())) {
+                String result = stop(ride.rider());
+                if (involved(ride.rider()) && reportedRefusals.add(ride.rider())) {
+                    notify(ride, result);
+                }
+            }
+        }
+    }
+    public boolean cleanup(UUID player) {
+        requests.values().removeIf(request -> request.sender().equals(player) || request.recipient().equals(player));
+        stop(player);
+        return !involved(player);
+    }
+    /** Returns server-refused dismounts; never bypasses cancellation or claims false detachment. */
+    public int close() {
+        closed = true;
+        requests.clear();
+        for (Ride ride : java.util.Set.copyOf(rides.values())) { stop(ride.rider()); }
+        return rides.size() / 2;
+    }
+    public boolean involved(UUID player) { return rides.containsKey(player); }
+}

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

@@ -0,0 +1,27 @@
+package games.dmg.spigotheights;
+
+import java.util.concurrent.Executor;
+import java.util.function.Consumer;
+
+/** Retains worker outcomes even if the plugin scheduler stops during disable. */
+public final class CompletionMailbox implements Executor {
+    private final Consumer<Runnable> wakeup;
+    private final java.util.concurrent.ConcurrentLinkedQueue<Runnable> ready = new java.util.concurrent.ConcurrentLinkedQueue<>();
+
+    public CompletionMailbox(Consumer<Runnable> wakeup) {
+        this.wakeup = wakeup;
+    }
+
+    @Override public void execute(Runnable task) {
+        ready.add(task);
+        wakeup.accept(this::drain);
+    }
+
+    /** Must be called on the main thread, also after the writer joins during disable. */
+    public void drain() {
+        Runnable task;
+        while ((task = ready.poll()) != null) {
+            task.run();
+        }
+    }
+}

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

@@ -7,34 +7,117 @@ import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
+import java.time.Instant;
+import java.time.format.DateTimeParseException;
 import java.util.UUID;
+import org.bukkit.configuration.InvalidConfigurationException;
 import org.bukkit.configuration.file.YamlConfiguration;
 
 public final class HeightStore {
     private final Path statePath;
-    private final YamlConfiguration state;
+    private volatile YamlConfiguration state;
+
+    public record Sequence(double baseline, Instant expiresAt) {}
 
     public HeightStore(File dataFolder) {
         statePath = dataFolder.toPath().resolve("state.yml");
         state = YamlConfiguration.loadConfiguration(statePath.toFile());
     }
 
-    public synchronized Double find(UUID playerId) {
+    public Double find(UUID playerId) {
+        YamlConfiguration snapshot = state;
         String path = path(playerId);
-        return state.contains(path) ? state.getDouble(path) : null;
+        return snapshot.contains(path) ? snapshot.getDouble(path) : null;
     }
 
-    public synchronized void save(UUID playerId, double scale) throws IOException {
-        state.set(path(playerId), scale);
+    public Sequence sequence(UUID playerId) {
+        YamlConfiguration snapshot = state;
+        String path = temporaryPath(playerId);
+        if (!snapshot.isDouble(path + ".baseline") && !snapshot.isInt(path + ".baseline")) {
+            return null;
+        }
+        double baseline = snapshot.getDouble(path + ".baseline");
+        if (!Double.isFinite(baseline) || baseline < 0.0625 || baseline > 16.0) {
+            return null;
+        }
+        try {
+            return new Sequence(baseline, Instant.parse(snapshot.getString(path + ".expires-at", "")));
+        } catch (DateTimeParseException exception) {
+            return null;
+        }
+    }
+
+    /** A permanent write also invalidates any outstanding temporary sequence. */
+    public void save(UUID playerId, double scale) throws IOException {
+        save(playerId, scale, null);
+    }
+
+    public boolean hasReceipt(UUID playerId, UUID source) {
+        return state.getBoolean(receiptPath(playerId, source));
+    }
+
+    public void save(UUID playerId, double scale, Sequence sequence) throws IOException {
+        save(playerId, scale, sequence, null);
+    }
+
+    public synchronized void save(UUID playerId, double scale, Sequence sequence, UUID source) throws IOException {
+        YamlConfiguration next = copy();
+        next.set(path(playerId), scale);
+        next.set(temporaryPath(playerId), null);
+        if (sequence != null) {
+            next.set(temporaryPath(playerId) + ".baseline", sequence.baseline());
+            next.set(temporaryPath(playerId) + ".expires-at", sequence.expiresAt().toString());
+        }
+        if (source != null) {
+            next.set(receiptPath(playerId, source), true);
+        }
+        replace(next);
+    }
+
+    public synchronized void forgetSource(UUID source) throws IOException {
+        var players = state.getConfigurationSection("players");
+        if (players == null) {
+            return;
+        }
+        java.util.List<String> paths = players.getKeys(false).stream()
+                .map(player -> "players." + player + ".throwables." + source)
+                .filter(state::contains).toList();
+        if (!paths.isEmpty()) {
+            YamlConfiguration next = copy();
+            paths.forEach(path -> next.set(path, null));
+            replace(next);
+        }
+    }
+
+    private YamlConfiguration copy() throws IOException {
+        YamlConfiguration next = new YamlConfiguration();
+        try {
+            next.loadFromString(state.saveToString());
+        } catch (InvalidConfigurationException exception) {
+            throw new IOException("Could not copy player state", exception);
+        }
+        return next;
+    }
+
+    private void replace(YamlConfiguration next) throws IOException {
         Files.createDirectories(statePath.getParent());
         Path temporary = statePath.resolveSibling("state.yml.tmp");
-        Files.writeString(temporary, state.saveToString(), StandardCharsets.UTF_8);
+        Files.writeString(temporary, next.saveToString(), StandardCharsets.UTF_8);
         try {
             Files.move(temporary, statePath, StandardCopyOption.ATOMIC_MOVE,
                     StandardCopyOption.REPLACE_EXISTING);
         } catch (AtomicMoveNotSupportedException exception) {
             Files.move(temporary, statePath, StandardCopyOption.REPLACE_EXISTING);
         }
+        state = next;
+    }
+
+    private static String receiptPath(UUID playerId, UUID source) {
+        return "players." + playerId + ".throwables." + source;
+    }
+
+    private static String temporaryPath(UUID playerId) {
+        return "players." + playerId + ".temporary";
     }
 
     private static String path(UUID playerId) {

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

@@ -0,0 +1,170 @@
+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>"
+            + " | /heights player <name> [scale]";
+    private final LiveHeightSettings settings;
+    private final Logger logger;
+    private final PlayerHeights players;
+    private final HeightSetter heightSetter;
+    private final java.util.function.BiConsumer<org.bukkit.entity.Player, String> carry;
+    private static final String CARRY_USAGE = "Usage: /heights carry accept|decline|stop";
+    private static final List<String> CARRY_ACTIONS = List.of("accept", "decline", "stop");
+
+    @FunctionalInterface
+    public interface HeightSetter {
+        void set(String name, double value, java.util.function.Consumer<String> reply) throws IOException;
+    }
+
+    public HeightsCommand(LiveHeightSettings settings, PlayerHeights players, Logger logger) {
+        this(settings, players, logger, (name, value, reply) -> reply.accept(players.set(name, value)));
+    }
+
+    public HeightsCommand(LiveHeightSettings settings, PlayerHeights players, Logger logger, HeightSetter heightSetter) {
+        this(settings, players, logger, heightSetter,
+                (player, action) -> player.sendMessage("Carrying is unavailable."));
+    }
+
+    public HeightsCommand(LiveHeightSettings settings, PlayerHeights players, Logger logger, HeightSetter heightSetter,
+            java.util.function.BiConsumer<org.bukkit.entity.Player, String> carry) {
+        this.settings = settings;
+        this.players = players;
+        this.logger = logger;
+        this.heightSetter = heightSetter;
+        this.carry = carry;
+    }
+
+    @Override
+    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
+        if (args.length > 0 && args[0].equalsIgnoreCase("carry")) {
+            if (!(sender instanceof org.bukkit.entity.Player player)) {
+                sender.sendMessage("Only players can use carry commands.");
+            } else if (args.length != 2 || !CARRY_ACTIONS.contains(args[1].toLowerCase(Locale.ROOT))) {
+                sender.sendMessage(CARRY_USAGE);
+            } else {
+                carry.accept(player, args[1].toLowerCase(Locale.ROOT));
+            }
+            return true;
+        }
+        if (!sender.hasPermission(PERMISSION)) {
+            sender.sendMessage("You do not have permission to manage Spigot Heights.");
+            return true;
+        }
+        if (args.length > 0 && args[0].equalsIgnoreCase("player")) {
+            return playerCommand(sender, args);
+        }
+        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;
+    }
+
+    private boolean playerCommand(CommandSender sender, String[] args) {
+        if (args.length != 2 && args.length != 3) {
+            sender.sendMessage(USAGE);
+            return true;
+        }
+        try {
+            if (args.length == 2) {
+                sender.sendMessage(players.describe(args[1]));
+            } else {
+                heightSetter.set(args[1], Double.parseDouble(args[2]), sender::sendMessage);
+            }
+        } catch (NumberFormatException exception) {
+            sender.sendMessage("Invalid scale: enter a finite number, for example 0.5 or 1.0.");
+        } catch (IllegalArgumentException exception) {
+            sender.sendMessage(exception.getMessage());
+        } catch (IOException exception) {
+            logger.warning("Could not save player height: " + exception.getMessage());
+            sender.sendMessage("Could not save player height. Their height is unchanged; check the server log.");
+        }
+        return true;
+    }
+
+    @Override
+    public List<String> onTabComplete(CommandSender sender, Command command, String alias, String[] args) {
+        boolean player = sender instanceof org.bukkit.entity.Player;
+        if (player && args.length == 2 && args[0].equalsIgnoreCase("carry")) {
+            return matching(CARRY_ACTIONS.stream(), args[1]);
+        }
+        if (!sender.hasPermission(PERMISSION)) {
+            return player && args.length == 1 ? matching(Stream.of("carry"), args[0]) : List.of();
+        }
+        if (args.length == 1) {
+            return matching(player ? Stream.of("carry", "settings", "set", "player")
+                    : Stream.of("settings", "set", "player"), args[0]);
+        }
+        if (args.length == 2 && args[0].equalsIgnoreCase("player")) {
+            return matching(players.names().stream(), args[1]);
+        }
+        if (args.length == 3 && args[0].equalsIgnoreCase("player")
+                && players.names().stream().anyMatch(name -> name.equalsIgnoreCase(args[1]))) {
+            HeightSettings current = settings.get();
+            return matching(Stream.of(current.minimum(), current.maximum(), 0.0625, 0.2, 0.4, 0.5, 1.0, 2.0, 3.0, 16.0)
+                    .distinct().sorted().filter(players::isValid).map(String::valueOf), args[2]);
+        }
+        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.toLowerCase(Locale.ROOT).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/PlayerHeights.java

@@ -0,0 +1,65 @@
+package games.dmg.spigotheights;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.UUID;
+import java.util.function.DoubleConsumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+/** Online-player operations, called on the server thread. */
+public final class PlayerHeights {
+    public record Target(UUID id, String name, double baseScale, double effectiveScale, DoubleConsumer applyScale) {}
+
+    private final Supplier<HeightSettings> settings;
+    private final HeightStore store;
+    private final Function<String, Target> lookup;
+    private final Supplier<List<String>> onlineNames;
+
+    public PlayerHeights(Supplier<HeightSettings> settings, HeightStore store,
+            Function<String, Target> lookup, Supplier<List<String>> onlineNames) {
+        this.settings = settings;
+        this.store = store;
+        this.lookup = lookup;
+        this.onlineNames = onlineNames;
+    }
+
+    public String describe(String name) {
+        Target target = requireTarget(name);
+        String message = target.name() + " has scale " + target.baseScale() + " (1.0 = normal)";
+        if (target.effectiveScale() != target.baseScale()) {
+            message += "; effective scale with modifiers: " + target.effectiveScale();
+        }
+        return message + ".";
+    }
+
+    public String set(String name, double value) throws IOException {
+        Target target = requireTarget(name);
+        if (!isValid(value)) {
+            HeightSettings current = settings.get();
+            throw new IllegalArgumentException("Scale must be a finite number between " + current.minimum()
+                    + " and " + current.maximum() + ", or exactly 1.0 for normal size.");
+        }
+        store.save(target.id(), value);
+        target.applyScale().accept(value);
+        return "Set " + target.name() + "'s base scale to " + value + ". Saved and active.";
+    }
+
+    public List<String> names() {
+        return onlineNames.get();
+    }
+
+    public boolean isValid(double value) {
+        HeightSettings current = settings.get();
+        return Double.isFinite(value) && (value == 1.0
+                || value >= current.minimum() && value <= current.maximum());
+    }
+
+    private Target requireTarget(String name) {
+        Target target = lookup.apply(name);
+        if (target == null) {
+            throw new IllegalArgumentException("No online player named '" + name + "'. Use their full name.");
+        }
+        return target;
+    }
+}

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

@@ -1,10 +1,14 @@
 package games.dmg.spigotheights;
 
+import java.util.Locale;
+import java.util.function.Function;
+import io.papermc.paper.potion.PotionMix;
 import net.kyori.adventure.text.Component;
 import net.kyori.adventure.text.format.NamedTextColor;
 import org.bukkit.Color;
 import org.bukkit.Material;
 import org.bukkit.NamespacedKey;
+import org.bukkit.Server;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.RecipeChoice;
 import org.bukkit.inventory.ShapedRecipe;
@@ -19,12 +23,22 @@ public final class PotionRecipes {
     static final String[] DIMINUTION_SHAPE = {"GAG", "ASA", "GFG"};
     static final String[] RESTORATION_SHAPE = {"GAG", "ASA", "GUG"};
 
-    private final JavaPlugin plugin;
+    private final Server server;
     private final NamespacedKey potionKindKey;
+    private final Function<Material, ItemStack> items;
 
     public PotionRecipes(JavaPlugin plugin) {
-        this.plugin = plugin;
-        potionKindKey = new NamespacedKey(plugin, "stature_potion");
+        this(plugin.getServer(), new NamespacedKey(plugin, "stature_potion"), ItemStack::new);
+    }
+
+    PotionRecipes(Server server, NamespacedKey potionKindKey, Function<Material, ItemStack> items) {
+        this.server = server;
+        this.potionKindKey = potionKindKey;
+        this.items = items;
+    }
+
+    private NamespacedKey key(String value) {
+        return new NamespacedKey(potionKindKey.getNamespace(), value);
     }
 
     public void register() {
@@ -32,10 +46,46 @@ public final class PotionRecipes {
         registerGrowth();
         registerDiminution();
         registerRestoration();
+        registerBrewing(server.getPotionBrewer());
+    }
+
+    public void registerBrewing(org.bukkit.potion.PotionBrewer brewer) {
+        for (StaturePotion kind : StaturePotion.values()) {
+            mix(brewer, kind, Material.POTION, Material.GUNPOWDER, Material.SPLASH_POTION);
+            mix(brewer, kind, Material.SPLASH_POTION, Material.DRAGON_BREATH, Material.LINGERING_POTION);
+        }
+    }
+
+    private void mix(org.bukkit.potion.PotionBrewer brewer, StaturePotion kind, Material source,
+            Material ingredient, Material target) {
+        NamespacedKey mixKey = mixKey(kind, target);
+        brewer.removePotionMix(mixKey);
+        brewer.addPotionMix(new PotionMix(mixKey, create(kind, target),
+                PotionMix.createPredicateChoice(item -> item != null && item.getType() == source
+                        && identify(item) == kind),
+                PotionMix.createPredicateChoice(item -> item != null && item.getType() == ingredient)));
+    }
+
+    public void unregisterBrewing() {
+        for (StaturePotion kind : StaturePotion.values()) {
+            server.getPotionBrewer().removePotionMix(mixKey(kind, Material.SPLASH_POTION));
+            server.getPotionBrewer().removePotionMix(mixKey(kind, Material.LINGERING_POTION));
+        }
+    }
+
+    private NamespacedKey mixKey(StaturePotion kind, Material target) {
+        return key((kind.name() + "_" + target.name()).toLowerCase(Locale.ROOT));
     }
 
     public ItemStack create(StaturePotion kind) {
-        ItemStack item = new ItemStack(Material.POTION);
+        return create(kind, Material.POTION);
+    }
+
+    public ItemStack create(StaturePotion kind, Material form) {
+        if (!isPotionForm(form)) {
+            throw new IllegalArgumentException("Unsupported potion form");
+        }
+        ItemStack item = items.apply(form);
         PotionMeta meta = (PotionMeta) item.getItemMeta();
         meta.displayName(Component.text(kind.displayName(), NamedTextColor.LIGHT_PURPLE));
         meta.getPersistentDataContainer().set(potionKindKey, PersistentDataType.STRING, kind.name());
@@ -45,7 +95,8 @@ public final class PotionRecipes {
     }
 
     public StaturePotion identify(ItemStack item) {
-        if (item == null || item.getType() != Material.POTION || !(item.getItemMeta() instanceof PotionMeta meta)) {
+        if (item == null || !isPotionForm(item.getType()) || !(item.getItemMeta() instanceof PotionMeta meta)
+                || !meta.getPersistentDataContainer().has(potionKindKey, PersistentDataType.STRING)) {
             return null;
         }
         String value = meta.getPersistentDataContainer().get(potionKindKey, PersistentDataType.STRING);
@@ -59,13 +110,17 @@ public final class PotionRecipes {
         }
     }
 
+    private static boolean isPotionForm(Material form) {
+        return form == Material.POTION || form == Material.SPLASH_POTION || form == Material.LINGERING_POTION;
+    }
+
     public boolean isAwkwardPotion(ItemStack item) {
         return item != null && item.getItemMeta() instanceof PotionMeta meta
                 && meta.getBasePotionType() == PotionType.AWKWARD;
     }
 
     public NamespacedKey shiftingKey() {
-        return new NamespacedKey(plugin, "shifting_stature");
+        return key("shifting_stature");
     }
 
     private void registerShifting() {
@@ -74,39 +129,39 @@ public final class PotionRecipes {
         recipe.setIngredient('A', Material.AMETHYST_SHARD);
         recipe.setIngredient('C', Material.CHORUS_FRUIT);
         recipe.setIngredient('W', Material.POTION);
-        plugin.getServer().addRecipe(recipe);
+        server.addRecipe(recipe);
     }
 
     private void registerGrowth() {
-        ShapedRecipe recipe = new ShapedRecipe(new NamespacedKey(plugin, "growth"), create(StaturePotion.GROWTH));
+        ShapedRecipe recipe = new ShapedRecipe(key("growth"), create(StaturePotion.GROWTH));
         recipe.shape(GROWTH_SHAPE);
         recipe.setIngredient('G', Material.GOLD_INGOT);
         recipe.setIngredient('A', Material.AMETHYST_SHARD);
         recipe.setIngredient('S', new RecipeChoice.ExactChoice(create(StaturePotion.SHIFTING)));
         recipe.setIngredient('R', Material.RABBIT_FOOT);
-        plugin.getServer().addRecipe(recipe);
+        server.addRecipe(recipe);
     }
 
     private void registerDiminution() {
-        ShapedRecipe recipe = new ShapedRecipe(new NamespacedKey(plugin, "diminution"),
+        ShapedRecipe recipe = new ShapedRecipe(key("diminution"),
                 create(StaturePotion.DIMINUTION));
         recipe.shape(DIMINUTION_SHAPE);
         recipe.setIngredient('G', Material.GOLD_INGOT);
         recipe.setIngredient('A', Material.AMETHYST_SHARD);
         recipe.setIngredient('S', new RecipeChoice.ExactChoice(create(StaturePotion.SHIFTING)));
         recipe.setIngredient('F', Material.FERMENTED_SPIDER_EYE);
-        plugin.getServer().addRecipe(recipe);
+        server.addRecipe(recipe);
     }
 
     private void registerRestoration() {
-        ShapedRecipe recipe = new ShapedRecipe(new NamespacedKey(plugin, "restoration"),
+        ShapedRecipe recipe = new ShapedRecipe(key("restoration"),
                 create(StaturePotion.RESTORATION));
         recipe.shape(RESTORATION_SHAPE);
         recipe.setIngredient('G', Material.GOLD_INGOT);
         recipe.setIngredient('A', Material.AMETHYST_SHARD);
         recipe.setIngredient('S', new RecipeChoice.ExactChoice(create(StaturePotion.SHIFTING)));
         recipe.setIngredient('U', Material.SUGAR);
-        plugin.getServer().addRecipe(recipe);
+        server.addRecipe(recipe);
     }
 
     private static Color color(StaturePotion kind) {

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

@@ -1,9 +1,14 @@
 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;
 
 public final class SpigotHeightsPlugin extends JavaPlugin {
+    private BukkitStatureService stature;
+    private PotionRecipes potions;
+    private BukkitCarry carry;
     @Override
     public void onEnable() {
         saveDefaultConfig();
@@ -16,15 +21,56 @@ 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());
+        });
         HeightStore store = new HeightStore(getDataFolder());
-        PotionRecipes potions = new PotionRecipes(this);
+        BukkitPlayerHeights onlinePlayers = new BukkitPlayerHeights(getServer());
+        PlayerHeights playerHeights = new PlayerHeights(liveSettings, store, onlinePlayers::find, onlinePlayers::names);
+        stature = new BukkitStatureService(this, liveSettings, store);
+        carry = new BukkitCarry(getServer(), liveSettings,
+                task -> getServer().getScheduler().runTask(this, task), getLogger());
+        getServer().getPluginManager().registerEvents(carry, this);
+        // Includes external attribute modifiers and US-009 expiry/admin updates; no movement-event scans.
+        getServer().getScheduler().runTaskTimer(this, carry::tick, 5L, 5L);
+        HeightsCommand executor = new HeightsCommand(liveSettings, playerHeights, getLogger(), stature::set, carry::command);
+        PluginCommand command = Objects.requireNonNull(getCommand("heights"), "Missing heights command declaration");
+        command.setExecutor(executor);
+        command.setTabCompleter(executor);
+
+        potions = new PotionRecipes(this);
         potions.register();
         getServer().getPluginManager().registerEvents(
-                new StatureListener(this, settings, store, potions), this);
-        getServer().getPluginManager().registerEvents(new TinyPlayerLauncher(settings), this);
+                new StatureListener(potions, stature::drink, stature::resume,
+                        task -> getServer().getScheduler().runTask(this, task)), this);
+        ThrowableStatureListener throwable = new ThrowableStatureListener(potions,
+                new org.bukkit.NamespacedKey(this, "cloud_kind"), stature::temporary);
+        getServer().getPluginManager().registerEvents(throwable, this);
+        StatureClouds clouds = new StatureClouds(getServer(), throwable, stature::retireSource);
+        getServer().getPluginManager().registerEvents(clouds, this);
+        getServer().getScheduler().runTaskTimer(this, clouds::tick, 5L, 5L);
+        getServer().getScheduler().runTaskTimer(this, stature::expireOnline, 20L, 20L);
+        getServer().getOnlinePlayers().forEach(stature::resume);
+        getServer().getPluginManager().registerEvents(new TinyPlayerLauncher(liveSettings), this);
         getLogger().info("Spigot Heights enabled.");
     }
 
+    @Override
+    public void onDisable() {
+        if (carry != null) {
+            carry.close();
+        }
+        if (stature != null) {
+            stature.close();
+        }
+        if (potions != null) {
+            potions.unregisterBrewing();
+        }
+    }
+
     static HeightSettings loadSettings(FileConfiguration config) {
         return new HeightSettings(
                 config.getDouble("height.minimum"),

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

@@ -0,0 +1,69 @@
+package games.dmg.spigotheights;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.UUID;
+import org.bukkit.Server;
+import org.bukkit.entity.AreaEffectCloud;
+import org.bukkit.entity.Entity;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.entity.LingeringPotionSplashEvent;
+import org.bukkit.event.world.EntitiesLoadEvent;
+import org.bukkit.event.world.EntitiesUnloadEvent;
+
+/** Tracks only loaded, authenticated Heights clouds; does not scan worlds every tick. */
+public final class StatureClouds implements Listener {
+    private final Server server;
+    private final ThrowableStatureListener listener;
+    private final java.util.function.Consumer<UUID> retire;
+    private final Map<UUID, AreaEffectCloud> clouds = new HashMap<>();
+
+    public StatureClouds(Server server, ThrowableStatureListener listener, java.util.function.Consumer<UUID> retire) {
+        this.server = server;
+        this.listener = listener;
+        this.retire = retire;
+        server.getWorlds().forEach(world -> world.getEntitiesByClass(AreaEffectCloud.class).forEach(this::track));
+    }
+
+    private void track(Entity entity) {
+        if (entity instanceof AreaEffectCloud cloud && listener.cloudKind(cloud) != null) {
+            clouds.put(cloud.getUniqueId(), cloud);
+        }
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void onCreate(LingeringPotionSplashEvent event) {
+        if (!event.isCancelled()) {
+            track(event.getAreaEffectCloud());
+        }
+    }
+
+    @EventHandler
+    public void onLoad(EntitiesLoadEvent event) {
+        event.getEntities().forEach(this::track);
+    }
+
+    @EventHandler
+    public void onUnload(EntitiesUnloadEvent event) {
+        event.getEntities().forEach(entity -> clouds.remove(entity.getUniqueId()));
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onRemove(org.bukkit.event.entity.EntityRemoveEvent event) {
+        if (event.getCause() != org.bukkit.event.entity.EntityRemoveEvent.Cause.UNLOAD
+                && listener.isStatureSource(event.getEntity())) {
+            clouds.remove(event.getEntity().getUniqueId());
+            retire.accept(event.getEntity().getUniqueId());
+        }
+    }
+
+    public void tick() {
+        clouds.values().removeIf(cloud -> !cloud.isValid());
+        // Event callbacks may load/unload entities; iterate a snapshot to avoid reentrant mutation.
+        for (AreaEffectCloud cloud : java.util.List.copyOf(clouds.values())) {
+            listener.tickCloud(cloud, server.getPluginManager()::callEvent);
+        }
+    }
+}

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

@@ -1,9 +1,9 @@
 package games.dmg.spigotheights;
 
-import java.io.IOException;
-import java.util.concurrent.ThreadLocalRandom;
-import org.bukkit.attribute.Attribute;
-import org.bukkit.attribute.AttributeInstance;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import org.bukkit.Keyed;
+import org.bukkit.Material;
 import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
@@ -14,20 +14,19 @@ import org.bukkit.event.player.PlayerJoinEvent;
 import org.bukkit.event.player.PlayerRespawnEvent;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.Recipe;
-import org.bukkit.Keyed;
-import org.bukkit.plugin.java.JavaPlugin;
 
 public final class StatureListener implements Listener {
-    private final JavaPlugin plugin;
-    private final HeightSettings settings;
-    private final HeightStore store;
     private final PotionRecipes potions;
+    private final BiConsumer<Player, StaturePotion> drink;
+    private final Consumer<Player> resume;
+    private final Consumer<Runnable> nextTick;
 
-    public StatureListener(JavaPlugin plugin, HeightSettings settings, HeightStore store, PotionRecipes potions) {
-        this.plugin = plugin;
-        this.settings = settings;
-        this.store = store;
+    public StatureListener(PotionRecipes potions, BiConsumer<Player, StaturePotion> drink,
+            Consumer<Player> resume, Consumer<Runnable> nextTick) {
         this.potions = potions;
+        this.drink = drink;
+        this.resume = resume;
+        this.nextTick = nextTick;
     }
 
     @EventHandler
@@ -44,50 +43,22 @@ public final class StatureListener implements Listener {
 
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onConsume(PlayerItemConsumeEvent event) {
-        StaturePotion kind = potions.identify(event.getItem());
-        if (kind == null) {
+        if (event.isCancelled() || event.getItem().getType() != Material.POTION) {
             return;
         }
-        Player player = event.getPlayer();
-        double current = currentScale(player);
-        double scale = kind.scaleAfterDrinking(current, settings,
-                bound -> ThreadLocalRandom.current().nextInt(bound));
-        applyAndSave(player, scale);
-        player.sendMessage("Your scale is now " + scale + ".");
+        StaturePotion kind = potions.identify(event.getItem());
+        if (kind != null) {
+            drink.accept(event.getPlayer(), kind);
+        }
     }
 
     @EventHandler
     public void onJoin(PlayerJoinEvent event) {
-        apply(event.getPlayer(), HeightMath.safeStoredScale(store.find(event.getPlayer().getUniqueId()), settings));
+        resume.accept(event.getPlayer());
     }
 
     @EventHandler
     public void onRespawn(PlayerRespawnEvent event) {
-        plugin.getServer().getScheduler().runTask(plugin, () -> {
-            Player player = event.getPlayer();
-            apply(player, HeightMath.safeStoredScale(store.find(player.getUniqueId()), settings));
-        });
-    }
-
-    private void applyAndSave(Player player, double scale) {
-        apply(player, scale);
-        try {
-            store.save(player.getUniqueId(), scale);
-        } catch (IOException exception) {
-            plugin.getLogger().severe("Could not save scale for " + player.getUniqueId() + ": "
-                    + exception.getMessage());
-        }
-    }
-
-    private static void apply(Player player, double scale) {
-        AttributeInstance attribute = player.getAttribute(Attribute.SCALE);
-        if (attribute != null) {
-            attribute.setBaseValue(scale);
-        }
-    }
-
-    private static double currentScale(Player player) {
-        AttributeInstance attribute = player.getAttribute(Attribute.SCALE);
-        return attribute == null ? 1.0 : attribute.getBaseValue();
+        nextTick.accept(() -> resume.accept(event.getPlayer()));
     }
 }

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

@@ -0,0 +1,77 @@
+package games.dmg.spigotheights;
+
+import java.util.ArrayDeque;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executor;
+import java.util.function.BiConsumer;
+import java.util.function.Supplier;
+
+/** Serializes main-thread capture, worker persistence, and main-thread completion. */
+public final class StatureQueue {
+    private final Executor worker;
+    private final Executor main;
+    private final ArrayDeque<Job> jobs = new ArrayDeque<>();
+    private boolean running;
+    private boolean closed;
+
+    private record Job(Supplier<Callable<Double>> prepare, BiConsumer<Double, Exception> complete) {}
+
+    public StatureQueue(Executor worker, Executor main) {
+        this.worker = worker;
+        this.main = main;
+    }
+
+    public void submit(Supplier<Callable<Double>> prepare, BiConsumer<Double, Exception> complete) {
+        if (closed) {
+            complete.accept(null, new IllegalStateException("Stature service is shutting down."));
+            return;
+        }
+        if (jobs.size() >= 256) {
+            complete.accept(null, new IllegalStateException("Too many pending stature operations; try again shortly."));
+            return;
+        }
+        jobs.addLast(new Job(prepare, complete));
+        start();
+    }
+
+    public void close() {
+        closed = true;
+        while (!jobs.isEmpty()) {
+            jobs.removeFirst().complete().accept(null, new IllegalStateException("Stature service is shutting down."));
+        }
+    }
+
+    private void start() {
+        if (running || jobs.isEmpty()) {
+            return;
+        }
+        running = true;
+        Job job = jobs.removeFirst();
+        try {
+            Callable<Double> work = job.prepare().get();
+            worker.execute(() -> {
+                Double result = null;
+                Exception failure = null;
+                try {
+                    result = work.call();
+                } catch (Exception exception) {
+                    failure = exception;
+                }
+                Double saved = result;
+                Exception error = failure;
+                main.execute(() -> finish(job, saved, error));
+            });
+        } catch (Exception exception) {
+            finish(job, null, exception);
+        }
+    }
+
+    private void finish(Job job, Double result, Exception error) {
+        try {
+            job.complete().accept(result, error);
+        } finally {
+            running = false;
+            start();
+        }
+    }
+}

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

@@ -0,0 +1,64 @@
+package games.dmg.spigotheights;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.UUID;
+import java.util.function.IntUnaryOperator;
+
+/** Durable stature operations, independent of the server. */
+public final class TemporaryStature {
+    private final HeightStore store;
+
+    public TemporaryStature(HeightStore store) {
+        this.store = store;
+    }
+
+    public Double applyOnce(UUID player, UUID source, double current, StaturePotion kind, HeightSettings settings,
+            Instant now, IntUnaryOperator random) throws IOException {
+        if (source != null && store.hasReceipt(player, source)) {
+            return null;
+        }
+        HeightStore.Sequence sequence = store.sequence(player);
+        if (sequence != null && !now.isBefore(sequence.expiresAt())) {
+            current = sequence.baseline();
+            sequence = null;
+        }
+        double baseline = sequence == null ? current : sequence.baseline();
+        double result = kind.scaleAfterDrinking(current, settings, random);
+        store.save(player, result, new HeightStore.Sequence(baseline, now.plusSeconds(300)), source);
+        return result;
+    }
+
+    public double apply(UUID player, double current, StaturePotion kind, HeightSettings settings,
+            Instant now, IntUnaryOperator random) throws IOException {
+        return applyOnce(player, null, current, kind, settings, now, random);
+    }
+
+    public double drink(UUID player, double current, StaturePotion kind, HeightSettings settings,
+            Instant now, IntUnaryOperator random) throws IOException {
+        HeightStore.Sequence sequence = store.sequence(player);
+        if (sequence != null && !now.isBefore(sequence.expiresAt())) {
+            current = sequence.baseline();
+        }
+        double result = kind.scaleAfterDrinking(current, settings, random);
+        store.save(player, result);
+        return result;
+    }
+
+    public void acknowledgeRestoration(UUID player, HeightStore.Sequence expected) throws IOException {
+        if (expected != null && expected.equals(store.sequence(player))
+                && Double.valueOf(expected.baseline()).equals(store.find(player))) {
+            store.save(player, expected.baseline());
+        }
+    }
+
+    public double resume(UUID player, HeightSettings settings, Instant now) throws IOException {
+        HeightStore.Sequence sequence = store.sequence(player);
+        if (sequence != null && !now.isBefore(sequence.expiresAt())) {
+            // Keep an expired restoration pending until the server actually applies its result.
+            store.save(player, sequence.baseline(), sequence);
+            return sequence.baseline();
+        }
+        return HeightMath.safeStoredScale(store.find(player), settings);
+    }
+}

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

@@ -0,0 +1,151 @@
+package games.dmg.spigotheights;
+
+import java.util.function.Consumer;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.entity.Entity;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.persistence.PersistentDataContainer;
+import org.bukkit.persistence.PersistentDataType;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Listener;
+import org.bukkit.event.entity.AreaEffectCloudApplyEvent;
+import org.bukkit.event.entity.LingeringPotionSplashEvent;
+import org.bukkit.event.entity.PotionSplashEvent;
+
+/** Bukkit delivery boundary; the effect service reports durable application success. */
+public final class ThrowableStatureListener implements Listener {
+    @FunctionalInterface
+    public interface Effects {
+        void apply(java.util.UUID source, Player player, StaturePotion kind, Consumer<Boolean> completed);
+    }
+
+    private final PotionRecipes potions;
+    private final NamespacedKey cloudKind;
+    private final Effects effects;
+    private record Delivery(java.util.UUID source, java.util.UUID player) {}
+    private final java.util.Set<Delivery> pending = new java.util.HashSet<>();
+
+    public ThrowableStatureListener(PotionRecipes potions, NamespacedKey cloudKind, Effects effects) {
+        this.potions = potions;
+        this.cloudKind = cloudKind;
+        this.effects = effects;
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void onSplash(PotionSplashEvent event) {
+        if (event.isCancelled() || event.getPotion().getItem().getType() != Material.SPLASH_POTION) {
+            return;
+        }
+        StaturePotion kind = potions.identify(event.getPotion().getItem());
+        if (kind == null) {
+            return;
+        }
+        for (var entity : event.getAffectedEntities()) {
+            if (entity instanceof Player player && event.getIntensity(entity) > 0) {
+                applyOnce(event.getPotion(), player, kind);
+            }
+        }
+    }
+
+    private void applyOnce(Entity source, Player player, StaturePotion kind) {
+        PersistentDataContainer data = source.getPersistentDataContainer();
+        NamespacedKey receipt = new NamespacedKey(cloudKind.getNamespace(), "hit_" + player.getUniqueId());
+        Delivery delivery = new Delivery(source.getUniqueId(), player.getUniqueId());
+        if (data.has(receipt) || !player.isOnline() || player.isDead() || !pending.add(delivery)) {
+            return;
+        }
+        // Pending reservations are not serialized by chunk unload. The service commits the
+        // successful receipt atomically with stature, so reload cannot duplicate an application.
+        try {
+            effects.apply(source.getUniqueId(), player, kind, success -> {
+                pending.remove(delivery);
+                if (success) {
+                    data.set(receipt, PersistentDataType.BYTE, (byte) 1);
+                }
+            });
+        } catch (RuntimeException exception) {
+            pending.remove(delivery);
+            throw exception;
+        }
+    }
+    @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
+    public void onLingering(LingeringPotionSplashEvent event) {
+        if (event.isCancelled() || event.getEntity().getItem().getType() != Material.LINGERING_POTION) {
+            return;
+        }
+        StaturePotion kind = potions.identify(event.getEntity().getItem());
+        if (kind != null) {
+            event.allowsEmptyCreation(true);
+            event.getAreaEffectCloud().getPersistentDataContainer().set(cloudKind,
+                    PersistentDataType.STRING, kind.name());
+        }
+    }
+
+    /** Empty vanilla clouds do not discover victims. Dispatch the normal cancellable event ourselves. */
+    public void tickCloud(org.bukkit.entity.AreaEffectCloud cloud, Consumer<AreaEffectCloudApplyEvent> dispatch) {
+        if (!cloud.isValid() || cloudKind(cloud) == null || cloud.getTicksLived() < cloud.getWaitTime()) {
+            return;
+        }
+        double radius = cloud.getRadius();
+        if (radius < 0.5) {
+            return;
+        }
+        var center = cloud.getLocation();
+        java.util.List<org.bukkit.entity.LivingEntity> targets = new java.util.ArrayList<>();
+        for (Entity entity : cloud.getNearbyEntities(radius, 0.5, radius)) {
+            if (entity instanceof Player player && player.isOnline() && !player.isDead()
+                    && player.getGameMode() != org.bukkit.GameMode.SPECTATOR
+                    && !hasReceipt(cloud, player) && cloud.getBoundingBox().overlaps(player.getBoundingBox())) {
+                var position = player.getLocation();
+                double x = position.getX() - center.getX();
+                double z = position.getZ() - center.getZ();
+                if (x * x + z * z <= radius * radius) {
+                    targets.add(player);
+                }
+            }
+        }
+        if (!targets.isEmpty()) {
+            dispatch.accept(new AreaEffectCloudApplyEvent(cloud, targets));
+        }
+    }
+
+    private boolean hasReceipt(Entity source, Player player) {
+        return pending.contains(new Delivery(source.getUniqueId(), player.getUniqueId()))
+                || source.getPersistentDataContainer().has(new NamespacedKey(cloudKind.getNamespace(),
+                        "hit_" + player.getUniqueId()));
+    }
+
+    boolean isStatureSource(Entity source) {
+        return source instanceof org.bukkit.entity.AreaEffectCloud cloud && cloudKind(cloud) != null
+                || source instanceof org.bukkit.entity.ThrownPotion thrown && potions.identify(thrown.getItem()) != null;
+    }
+
+    StaturePotion cloudKind(org.bukkit.entity.AreaEffectCloud cloud) {
+        PersistentDataContainer data = cloud.getPersistentDataContainer();
+        if (!data.has(cloudKind, PersistentDataType.STRING)) {
+            return null;
+        }
+        try {
+            return StaturePotion.valueOf(data.get(cloudKind, PersistentDataType.STRING));
+        } catch (IllegalArgumentException exception) {
+            return null;
+        }
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void onCloud(AreaEffectCloudApplyEvent event) {
+        if (event.isCancelled()) {
+            return;
+        }
+        StaturePotion kind = cloudKind(event.getEntity());
+        if (kind != null) {
+            for (var entity : event.getAffectedEntities()) {
+                if (entity instanceof Player player) {
+                    applyOnce(event.getEntity(), player, kind);
+                }
+            }
+        }
+    }
+}

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) {
-        this.settings = settings;
+    public TinyPlayerLauncher(Supplier<HeightSettings> settingsSupplier) {
+        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 +4,11 @@ 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: Request consensual carrying or administer stature settings and player heights.
+    usage: /heights carry accept|decline|stop | /heights settings | /heights set min|max <value> | /heights player <name> [scale]
+permissions:
+  spigotheights.admin:
+    description: View and change Spigot Heights settings and player heights.
+    default: op

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

@@ -0,0 +1,290 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.*;
+import java.util.*;
+import java.util.logging.Logger;
+import org.bukkit.*;
+import org.bukkit.entity.*;
+import org.bukkit.event.player.PlayerInteractEntityEvent;
+import org.bukkit.inventory.EquipmentSlot;
+import org.junit.jupiter.api.Test;
+
+@SuppressWarnings("removal") // Construct declared-Purpur events without installing a server.
+class BukkitCarryTest {
+    private final UUID worldId = UUID.randomUUID();
+    private final World world = BukkitDoubles.proxy(World.class, (p, m, a) -> {
+        if (m.getName().equals("getUID")) { return worldId; }
+        throw new UnsupportedOperationException(m.getName());
+    });
+    private final Actor small = new Actor("Small", 0.4, 0), large = new Actor("Large", 1, 1);
+    private final List<Runnable> scheduled = new ArrayList<>();
+    private final List<String> warnings = new ArrayList<>();
+    private final Logger logger = new Logger("carry-test", null) {
+        @Override public void warning(String message) { warnings.add(message); }
+        @Override public void severe(String message) { warnings.add(message); }
+    };
+    private boolean dismountAllowed = true, reenterStop, invalidMountTopology;
+    private int nativeDismounts;
+    private final BukkitCarry carry = new BukkitCarry(id -> id.equals(small.id) ? small.player
+            : id.equals(large.id) ? large.player : null,
+            () -> new HeightSettings(0.4, 2, 0.1, 0.5, 1.5, 20), scheduled::add, logger,
+            p -> actor(p).scale, () -> 0);
+
+    private Actor actor(Player p) { return p == small.player ? small : large; }
+    private final class Actor {
+        final UUID id = UUID.randomUUID();
+        final List<String> messages = new ArrayList<>();
+        final List<Entity> passengers = new ArrayList<>();
+        final Player player;
+        Entity vehicle;
+        Location location;
+        double scale;
+        boolean sneaking = true, online = true, dead;
+        Actor(String name, double scale, double x) {
+            this.scale = scale; location = new Location(world, x, 64, 0);
+            player = BukkitDoubles.proxy(Player.class, (p, m, a) -> switch (m.getName()) {
+                case "getUniqueId" -> id;
+                case "getName" -> name;
+                case "getWorld" -> world;
+                case "getLocation" -> location.clone();
+                case "isOnline", "isValid" -> online;
+                case "isDead" -> dead;
+                case "isSleeping" -> false;
+                case "getGameMode" -> GameMode.SURVIVAL;
+                case "isSneaking" -> sneaking;
+                case "isInsideVehicle" -> vehicle != null;
+                case "getVehicle" -> vehicle;
+                case "getPassengers" -> List.copyOf(passengers);
+                case "addPassenger" -> {
+                    Player rider = (Player) a[0]; passengers.add(rider); actor(rider).vehicle = (Entity) p;
+                    if (invalidMountTopology) {
+                        UUID otherId = UUID.randomUUID();
+                        vehicle = BukkitDoubles.proxy(Entity.class, (entity, method, args) -> {
+                            if (method.getName().equals("getUniqueId")) { return otherId; }
+                            throw new UnsupportedOperationException(method.getName());
+                        });
+                    }
+                    yield true;
+                }
+                case "leaveVehicle" -> {
+                    nativeDismounts++;
+                    if (reenterStop) {
+                        reenterStop = false;
+                        carry.command((Player) p, "stop");
+                    }
+                    if (vehicle != null) {
+                        var event = new org.bukkit.event.entity.EntityDismountEvent((Player) p, vehicle, true);
+                        if (!dismountAllowed) { event.setCancelled(true); }
+                        carry.dismountEvent(event);
+                        if (!event.isCancelled()) {
+                            actor((Player) vehicle).passengers.removeIf(e -> e == p); vehicle = null;
+                        }
+                    }
+                    yield true; // Intentionally misleading: adapter must check actual native attachment.
+                }
+                case "sendMessage" -> { messages.add((String) a[0]); yield null; }
+                case "equals" -> p == a[0];
+                case "hashCode" -> id.hashCode();
+                case "toString" -> name;
+                case "teleport", "setFallDistance", "setVelocity", "setInvulnerable", "eject", "removePassenger" ->
+                        throw new AssertionError("Native dismount must not rescue, reset motion, or eject other passengers");
+                default -> throw new UnsupportedOperationException(m.getName());
+            });
+        }
+    }
+    private PlayerInteractEntityEvent click(Actor from, Actor to, EquipmentSlot hand, boolean cancelled) {
+        PlayerInteractEntityEvent event = new PlayerInteractEntityEvent(from.player, to.player, hand);
+        event.setCancelled(cancelled); carry.interact(event); return event;
+    }
+    private void start() {
+        click(small, large, EquipmentSlot.HAND, false); carry.command(large.player, "accept");
+        assertSame(large.player, small.vehicle);
+    }
+    private void drain() {
+        List<Runnable> tasks = List.copyOf(scheduled); scheduled.clear(); tasks.forEach(Runnable::run);
+    }
+    @Test
+    void startsWithoutSafeGroundAndNativeStopDoesNotTeleportOrResetMotion() {
+        start();
+        Location before = small.location.clone();
+        carry.command(small.player, "stop");
+        assertEquals(1, nativeDismounts);
+        assertNull(small.vehicle);
+        assertEquals(before, small.location);
+    }
+    @Test
+    void carrierCanAlsoStopUsingOnlyTheRidersNativeDismount() {
+        start();
+        carry.command(large.player, "stop");
+        assertEquals(1, nativeDismounts);
+        assertNull(small.vehicle);
+    }
+    @Test
+    void preventsNestedMountsButDoesNotCancelNaturalSneakDismount() {
+        start();
+        var nested = new org.bukkit.event.entity.EntityMountEvent(large.player, small.player);
+        carry.mountEvent(nested);
+        assertTrue(nested.isCancelled());
+        var exit = new org.bukkit.event.entity.EntityDismountEvent(small.player, large.player, true);
+        carry.dismountEvent(exit);
+        assertFalse(exit.isCancelled());
+        small.player.leaveVehicle();
+        drain();
+        assertNull(small.vehicle);
+        assertEquals(1, nativeDismounts);
+        start(); // The native detach also cleared Heights' pair tracking.
+    }
+    @Test
+    void allowedTeleportDetachesWithoutCancellingOrReplayingTeleport() {
+        start();
+        var event = new org.bukkit.event.player.PlayerTeleportEvent(
+                large.player, large.location, new Location(world, 50, 70, 50));
+        event.setCancelled(true); carry.teleportEvent(event); drain();
+        assertSame(large.player, small.vehicle);
+        event.setCancelled(false); carry.teleportEvent(event);
+        assertFalse(event.isCancelled());
+        assertNull(small.vehicle);
+        assertEquals(1, nativeDismounts);
+        assertEquals(50, event.getTo().getX());
+    }
+    @Test
+    void nativeCancellationIsNotMistakenForDetachmentAndCanBeRetried() {
+        start(); dismountAllowed = false;
+        carry.command(small.player, "stop");
+        assertSame(large.player, small.vehicle);
+        assertTrue(small.messages.stream().anyMatch(m -> m.contains("refused")));
+        dismountAllowed = true;
+        carry.tick();
+        assertEquals(1, nativeDismounts, "A cancelled voluntary stop is not an automatic rescue/retry job");
+        carry.command(large.player, "stop");
+        assertNull(small.vehicle);
+        assertEquals(2, nativeDismounts);
+    }
+    @Test
+    void refusedDismountPreventsTeleportFromMovingTheActivePair() {
+        start(); dismountAllowed = false;
+        var event = new org.bukkit.event.player.PlayerTeleportEvent(
+                large.player, large.location, new Location(world, 50, 70, 50));
+        carry.teleportEvent(event);
+        assertTrue(event.isCancelled());
+        assertSame(large.player, small.vehicle);
+    }
+    @Test
+    void quitCleansBothRolesIncludingAnOfflineRiderWithoutRescue() {
+        start();
+        carry.quit(new org.bukkit.event.player.PlayerQuitEvent(large.player, (net.kyori.adventure.text.Component) null));
+        assertNull(small.vehicle);
+        start(); small.online = false;
+        carry.quit(new org.bukkit.event.player.PlayerQuitEvent(small.player, (net.kyori.adventure.text.Component) null));
+        assertNull(small.vehicle);
+        assertTrue(warnings.isEmpty());
+    }
+    @Test
+    void cancelledPurpurDeathDoesNotStopRideButActualDeathDoesForEitherRole() {
+        for (Actor actor : List.of(large, small)) {
+            start();
+            var death = new org.bukkit.event.entity.PlayerDeathEvent(
+                    actor.player, null, List.of(), 0, (net.kyori.adventure.text.Component) null, true);
+            death.setCancelled(true); carry.death(death);
+            assertSame(large.player, small.vehicle);
+            death.setCancelled(false); actor.dead = true; carry.death(death);
+            assertNull(small.vehicle);
+            actor.dead = false;
+        }
+        assertEquals(2, nativeDismounts);
+    }
+    @Test
+    void effectiveScaleChangesUseNativeCleanupAndRespectRefusals() {
+        start(); small.scale = 0.9; dismountAllowed = false;
+        carry.tick();
+        assertSame(large.player, small.vehicle);
+        dismountAllowed = true; carry.tick();
+        assertNull(small.vehicle);
+    }
+    @Test
+    void disableUsesNativeDismountAndReportsServerRefusalsWithoutClaimingSuccess() {
+        start(); dismountAllowed = false;
+        carry.close();
+        assertSame(large.player, small.vehicle);
+        assertTrue(warnings.stream().anyMatch(w -> w.contains("refused")));
+        dismountAllowed = true; carry.close();
+        assertNull(small.vehicle);
+    }
+    @Test
+    void nonCancellableNativeDismountNeedsNoRescueOrWarning() {
+        start();
+        var event = new org.bukkit.event.entity.EntityDismountEvent(small.player, large.player, false);
+        carry.dismountEvent(event);
+        assertFalse(event.isCancelled());
+        large.passengers.clear(); small.vehicle = null; // Native forced detachment after event dispatch.
+        drain();
+        assertEquals(0, nativeDismounts);
+        assertTrue(warnings.isEmpty());
+        start();
+    }
+    @Test
+    void partialNativeMountIsTrackedUntilItsInvalidRelationshipCanBeDetached() {
+        invalidMountTopology = true; dismountAllowed = false;
+        click(small, large, EquipmentSlot.HAND, false); carry.command(large.player, "accept");
+        assertSame(large.player, small.vehicle);
+        assertEquals(1, nativeDismounts, "Attempt native cleanup of a partially successful invalid mount");
+        assertFalse(large.messages.getLast().contains("started"));
+        dismountAllowed = true;
+        carry.command(small.player, "stop");
+        assertNull(small.vehicle);
+        assertEquals(2, nativeDismounts);
+        assertNotNull(large.vehicle, "Do not eject an unrelated relationship owned by another plugin");
+    }
+    @Test
+    void synchronousPluginReentryCannotRecursivelyDismountTheSameRider() {
+        start(); reenterStop = true;
+        carry.command(small.player, "stop");
+        assertEquals(1, nativeDismounts);
+        assertNull(small.vehicle);
+        assertEquals("Carry ended.", small.messages.getLast());
+    }
+    @Test
+    void cancelledNaturalDismountIsNotRetriedAndLateCancellationIsObserved() {
+        start(); dismountAllowed = false;
+        small.player.leaveVehicle();
+        drain();
+        assertSame(large.player, small.vehicle);
+        assertEquals(1, nativeDismounts);
+        var lateCancelled = new org.bukkit.event.entity.EntityDismountEvent(small.player, large.player, true);
+        carry.dismountEvent(lateCancelled);
+        lateCancelled.setCancelled(true);
+        drain();
+        assertSame(large.player, small.vehicle);
+        assertEquals(1, nativeDismounts);
+    }
+    @Test
+    void stalePairDoesNotEjectRiderFromAnUnrelatedVehicle() {
+        start();
+        UUID otherId = UUID.randomUUID();
+        Entity unrelated = BukkitDoubles.proxy(Entity.class, (p, method, args) -> {
+            if (method.getName().equals("getUniqueId")) { return otherId; }
+            throw new UnsupportedOperationException(method.getName());
+        });
+        large.passengers.clear(); small.vehicle = unrelated;
+        carry.tick();
+        assertSame(unrelated, small.vehicle);
+        assertEquals(0, nativeDismounts);
+        carry.command(large.player, "stop");
+        assertEquals("No active ride.", large.messages.getLast());
+    }
+    @Test
+    void onlySneakingUncancelledMainHandRequestsMountAfterAcceptance() {
+        click(small, large, EquipmentSlot.HAND, true);
+        click(small, large, EquipmentSlot.OFF_HAND, false);
+        small.sneaking = false; click(small, large, EquipmentSlot.HAND, false); small.sneaking = true;
+        assertTrue(large.messages.isEmpty());
+        assertTrue(click(small, large, EquipmentSlot.HAND, false).isCancelled());
+        assertFalse(large.messages.isEmpty());
+        assertTrue(large.passengers.isEmpty());
+        carry.command(large.player, "accept");
+        assertSame(large.player, small.vehicle);
+        assertEquals(List.of(small.player), large.passengers);
+        carry.command(large.player, "stop");
+        assertNull(small.vehicle);
+    }
+}

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

@@ -0,0 +1,65 @@
+package games.dmg.spigotheights;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Proxy;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.meta.PotionMeta;
+import org.bukkit.persistence.PersistentDataContainer;
+import org.bukkit.persistence.PersistentDataType;
+
+/** Small boundary doubles: no server installation or mocked domain rules. */
+final class BukkitDoubles {
+    private BukkitDoubles() {}
+
+    static <T> T proxy(Class<T> type, InvocationHandler handler) {
+        return type.cast(Proxy.newProxyInstance(type.getClassLoader(), new Class<?>[] {type}, handler));
+    }
+
+    static PersistentDataContainer container() {
+        Map<NamespacedKey, Object> values = new HashMap<>();
+        Map<NamespacedKey, PersistentDataType<?, ?>> types = new HashMap<>();
+        return proxy(PersistentDataContainer.class, (proxy, method, args) -> {
+            return switch (method.getName()) {
+                case "set" -> {
+                    values.put((NamespacedKey) args[0], args[2]);
+                    types.put((NamespacedKey) args[0], (PersistentDataType<?, ?>) args[1]);
+                    yield null;
+                }
+                case "get" -> types.get(args[0]) == args[1] ? values.get(args[0]) : null;
+                case "has" -> values.containsKey(args[0]) && (args.length == 1 || types.get(args[0]) == args[1]);
+                case "remove" -> { types.remove(args[0]); values.remove(args[0]); yield null; }
+                case "getKeys" -> Set.copyOf(values.keySet());
+                case "isEmpty" -> values.isEmpty();
+                default -> throw new UnsupportedOperationException(method.getName());
+            };
+        });
+    }
+
+    static final class Item extends ItemStack {
+        private final Material material;
+        private final PersistentDataContainer data = container();
+        private Object displayName;
+        private final PotionMeta meta = proxy(PotionMeta.class, (proxy, method, args) -> {
+            return switch (method.getName()) {
+                case "getPersistentDataContainer" -> data;
+                case "displayName" -> {
+                    if (args != null && args.length == 1) { displayName = args[0]; yield null; }
+                    yield displayName;
+                }
+                case "setColor" -> null;
+                default -> throw new UnsupportedOperationException(method.getName());
+            };
+        });
+
+        Item(Material material) { this.material = material; }
+        @Override public Material getType() { return material; }
+        @Override public PotionMeta getItemMeta() { return meta; }
+        @Override public boolean setItemMeta(org.bukkit.inventory.meta.ItemMeta value) { return value == meta; }
+        @Override public Item clone() { return this; }
+    }
+}

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

@@ -0,0 +1,20 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+class CarryPolicyTest {
+    @Test
+    void requiresThreeCurrentStepsWithDecimalBoundaryTolerance() {
+        assertTrue(CarryPolicy.eligible(1.0, 0.7, 0.1));
+        assertTrue(CarryPolicy.eligible(0.7, 0.4, 0.1));
+        assertFalse(CarryPolicy.eligible(1.0, 0.700001, 0.1));
+        assertFalse(CarryPolicy.eligible(1.0, 0.7, 0.2));
+        assertFalse(CarryPolicy.eligible(0.7, 1.0, 0.1));
+        for (double invalid : new double[] {0, -1, Double.NaN, Double.POSITIVE_INFINITY}) {
+            assertFalse(CarryPolicy.eligible(invalid, 0.4, 0.1));
+            assertFalse(CarryPolicy.eligible(1, invalid, 0.1));
+            assertFalse(CarryPolicy.eligible(1, 0.4, invalid));
+        }
+    }
+}

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

@@ -0,0 +1,189 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.*;
+import java.util.*;
+import org.junit.jupiter.api.Test;
+
+class CarryServiceTest {
+    private final UUID small = UUID.randomUUID(), large = UUID.randomUUID(), third = UUID.randomUUID();
+    private final Map<UUID, CarryService.State> states = new HashMap<>(Map.of(
+            small, new CarryService.State(0.4, true, true),
+            large, new CarryService.State(1, true, true),
+            third, new CarryService.State(2, true, true)));
+    private long now;
+    private double step = 0.1;
+    private boolean near = true, mountAllowed = true, stopAllowed = true, attached;
+    private int mounts, stops;
+    private UUID mountedCarrier, mountedRider;
+    private final List<String> messages = new ArrayList<>();
+    private final CarryService service = new CarryService(new CarryService.Port() {
+        public CarryService.State state(UUID id) { return states.get(id); }
+        public boolean nearby(UUID a, UUID b) { return near; }
+        public boolean mount(UUID carrier, UUID rider) {
+            mounts++; mountedCarrier = carrier; mountedRider = rider;
+            attached = mountAllowed; return mountAllowed;
+        }
+        public boolean attached(UUID carrier, UUID rider) { return attached; }
+        public boolean linked(UUID carrier, UUID rider) { return attached; }
+        public boolean dismount(UUID carrier, UUID rider) {
+            stops++;
+            if (stopAllowed) { attached = false; }
+            return stopAllowed;
+        }
+        public void message(UUID id, String text) { messages.add(text); }
+    }, () -> step, () -> now);
+
+    @Test
+    void consentExpiresAtThirtySecondsAndRechecksLiveConditions() {
+        service.request(small, large);
+        now = 30_000;
+        assertFalse(service.accept(large).contains("started"));
+        assertEquals(0, mounts);
+        for (int change = 0; change < 4; change++) {
+            near = true; step = 0.1;
+            states.put(small, new CarryService.State(0.4, true, true));
+            service.request(small, large);
+            switch (change) {
+                case 0 -> near = false;
+                case 1 -> step = 0.3;
+                case 2 -> states.put(small, new CarryService.State(0.8, true, true));
+                case 3 -> states.put(small, new CarryService.State(0.4, false, true));
+                default -> throw new AssertionError();
+            }
+            assertFalse(service.accept(large).contains("started"));
+            assertEquals(0, mounts);
+        }
+        near = true; step = 0.1;
+        states.put(small, new CarryService.State(0.4, true, true));
+        service.request(small, large);
+        now += 29_999;
+        assertTrue(service.accept(large).contains("started"));
+    }
+
+    @Test
+    void eitherParticipantCanWithdrawPendingConsentWithStop() {
+        for (UUID caller : List.of(small, large)) {
+            assertTrue(service.request(small, large).contains("sent"));
+            assertTrue(service.stop(caller).contains("cancelled"));
+            assertTrue(service.accept(large).contains("No pending"));
+            assertEquals(0, mounts);
+        }
+    }
+
+    @Test
+    void automaticNativeRefusalIsReportedOnceRatherThanSilentlyRetried() {
+        service.request(small, large); service.accept(large);
+        messages.clear();
+        states.put(small, new CarryService.State(0.9, true, true));
+        stopAllowed = false;
+        service.tick(); service.tick();
+        assertEquals(2, messages.size(), "Notify both participants once, not every tick");
+        assertTrue(messages.stream().allMatch(message -> message.contains("refused")));
+        assertTrue(service.involved(small));
+        stopAllowed = true; service.tick();
+        assertFalse(service.involved(small));
+    }
+
+    @Test
+    void reservesOneRequestPerPlayerAndDeclineReleasesBoth() {
+        assertTrue(service.request(small, large).contains("sent"));
+        assertFalse(service.request(third, large).contains("sent"));
+        assertFalse(service.request(small, third).contains("sent"));
+        assertTrue(service.decline(large).contains("declined"));
+        assertTrue(service.request(small, third).contains("sent"));
+        now = 30_000;
+        service.tick();
+        assertTrue(service.request(small, large).contains("sent"));
+    }
+
+    @Test
+    void rejectsExistingPassengersVehiclesAndActiveRidesAndFailedMounts() {
+        for (UUID busy : List.of(small, large)) {
+            CarryService.State before = states.get(busy);
+            states.put(busy, new CarryService.State(before.scale(), true, false));
+            assertFalse(service.request(small, large).contains("sent"));
+            states.put(busy, before);
+        }
+        service.request(small, large);
+        states.put(small, new CarryService.State(0.4, true, false));
+        assertFalse(service.accept(large).contains("started"));
+        states.put(small, new CarryService.State(0.4, true, true));
+        service.request(small, large);
+        mountAllowed = false;
+        assertFalse(service.accept(large).contains("started"));
+        assertFalse(service.involved(small));
+        mountAllowed = true;
+        service.request(small, large);
+        service.accept(large);
+        assertFalse(service.request(third, large).contains("sent"));
+        assertFalse(service.request(small, third).contains("sent"));
+    }
+
+    @Test
+    void lossOfEligibilityAttemptsNativeStopAndRefusedVoluntaryStopsRemainAccuratelyTracked() {
+        service.request(small, large); service.accept(large);
+        stopAllowed = false;
+        states.put(small, new CarryService.State(0.9, true, true));
+        service.tick();
+        assertEquals(1, stops);
+        assertTrue(service.involved(small));
+        assertTrue(service.stop(large).contains("refused"));
+        // No pending rescue job: if eligibility recovers, a voluntary stop can be requested again.
+        states.put(small, new CarryService.State(0.4, true, true));
+        stopAllowed = true;
+        service.tick();
+        assertTrue(service.involved(small));
+        assertTrue(service.stop(small).contains("ended"));
+        assertFalse(service.involved(small));
+        assertFalse(service.involved(large));
+    }
+
+    @Test
+    void lifecycleClearsRequestsAndRidesAndReportsUnresolvedDisable() {
+        service.request(small, large);
+        assertTrue(service.cleanup(small));
+        assertTrue(service.accept(large).contains("No pending"));
+        service.request(small, large); service.accept(large);
+        assertTrue(service.cleanup(large));
+        assertFalse(service.involved(small));
+        service.request(small, large); service.accept(large);
+        stopAllowed = false;
+        assertFalse(service.cleanup(small));
+        assertEquals(1, service.close());
+        assertTrue(service.involved(small));
+        assertFalse(service.request(third, large).contains("sent"));
+        stopAllowed = true;
+        assertEquals(0, service.close());
+    }
+
+    @Test
+    void unavailableOrDetachedParticipantsTriggerCleanup() {
+        service.request(small, large); service.accept(large);
+        attached = false;
+        service.tick();
+        assertEquals(1, stops);
+        assertFalse(service.involved(large));
+        service.request(small, large); service.accept(large);
+        states.put(large, new CarryService.State(1, false, false));
+        service.tick();
+        assertEquals(2, stops);
+        assertFalse(service.involved(large));
+    }
+
+    @Test
+    void eitherDirectionRequiresOtherPlayersExplicitConsent() {
+        for (boolean pickup : new boolean[] {false, true}) {
+            UUID sender = pickup ? large : small, recipient = pickup ? small : large;
+            assertTrue(service.request(sender, recipient).contains("sent"));
+            assertEquals(0, mounts);
+            assertTrue(service.accept(sender).contains("No pending"));
+            assertTrue(service.accept(recipient).contains("started"));
+            assertEquals(large, mountedCarrier);
+            assertEquals(small, mountedRider);
+            assertTrue(service.involved(small));
+            assertTrue(service.involved(large));
+            assertTrue(service.stop(sender).contains("ended"));
+            mounts = 0;
+        }
+    }
+}

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

@@ -0,0 +1,22 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class CompletionMailboxTest {
+    @Test
+    void shutdownCanDrainExactlyOnceEvenWhenScheduledWakeupWasDropped() {
+        List<Runnable> scheduled = new ArrayList<>();
+        List<String> results = new ArrayList<>();
+        CompletionMailbox mailbox = new CompletionMailbox(scheduled::add);
+        mailbox.execute(() -> results.add("failed save released reservation"));
+        assertEquals(List.of(), results);
+        mailbox.drain();
+        assertEquals(List.of("failed save released reservation"), results);
+        scheduled.forEach(Runnable::run);
+        mailbox.drain();
+        assertEquals(1, results.size());
+    }
+}

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

@@ -1,6 +1,9 @@
 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;
@@ -12,6 +15,18 @@ class HeightStoreTest {
     @TempDir
     Path temporaryDirectory;
 
+    @Test
+    void failedSaveDoesNotChangeCachedOrSavedScale() throws Exception {
+        UUID playerId = UUID.randomUUID();
+        HeightStore store = new HeightStore(temporaryDirectory.toFile());
+        store.save(playerId, 0.7);
+        String original = Files.readString(temporaryDirectory.resolve("state.yml"));
+        Files.createDirectory(temporaryDirectory.resolve("state.yml.tmp"));
+        assertThrows(IOException.class, () -> store.save(playerId, 0.2));
+        assertEquals(0.7, store.find(playerId));
+        assertEquals(original, Files.readString(temporaryDirectory.resolve("state.yml")));
+    }
+
     @Test
     void restorationReplacesPreviousSizeAndSurvivesReloadOutsideLimits() throws Exception {
         UUID playerId = UUID.randomUUID();
@@ -25,6 +40,23 @@ class HeightStoreTest {
         assertEquals(1.0, HeightMath.safeStoredScale(reloaded.find(playerId), settings));
     }
 
+    @Test
+    void sourceRemovalRetiresOnlyItsReceiptsWithoutChangingStature() throws Exception {
+        UUID player = UUID.randomUUID();
+        UUID source = UUID.randomUUID();
+        UUID other = UUID.randomUUID();
+        HeightStore store = new HeightStore(temporaryDirectory.toFile());
+        HeightStore.Sequence sequence = new HeightStore.Sequence(1.0, java.time.Instant.EPOCH.plusSeconds(300));
+        store.save(player, 0.8, sequence, source);
+        store.save(player, 0.6, sequence, other);
+        store.forgetSource(source);
+        HeightStore reloaded = new HeightStore(temporaryDirectory.toFile());
+        assertEquals(false, reloaded.hasReceipt(player, source));
+        assertEquals(true, reloaded.hasReceipt(player, other));
+        assertEquals(0.6, reloaded.find(player));
+        assertEquals(sequence, reloaded.sequence(player));
+    }
+
     @Test
     void storesByUuidAndPreservesUnknownYamlFields() throws Exception {
         UUID playerId = UUID.randomUUID();

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

@@ -0,0 +1,226 @@
+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.nio.file.Path;
+import java.util.UUID;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.logging.Logger;
+import org.bukkit.command.CommandSender;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.io.TempDir;
+
+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);
+    @TempDir
+    Path directory;
+    private final UUID playerId = UUID.randomUUID();
+    private double playerScale = 0.7;
+    private PlayerHeights players;
+    private HeightStore playerStore;
+    private HeightsCommand command;
+
+    @BeforeEach
+    void setup() {
+        playerStore = new HeightStore(directory.toFile());
+        players = new PlayerHeights(live, playerStore, name -> name.equalsIgnoreCase("Steve")
+                ? new PlayerHeights.Target(playerId, "Steve", playerScale, playerScale, value -> playerScale = value)
+                : null, () -> List.of("Steve"));
+        command = new HeightsCommand(live, players, Logger.getAnonymousLogger());
+    }
+
+    @Test
+    void nonAdminPlayersCanUseOnlySafeCarryActionsAndCompletion() throws Exception {
+        List<String> actions = new ArrayList<>();
+        org.bukkit.entity.Player player = BukkitDoubles.proxy(org.bukkit.entity.Player.class, (p, method, args) -> {
+            if (method.getName().equals("hasPermission")) { return false; }
+            if (method.getName().equals("sendMessage")) { messages.add((String) args[0]); return null; }
+            throw new UnsupportedOperationException(method.getName());
+        });
+        command = new HeightsCommand(live, players, Logger.getAnonymousLogger(),
+                (name, value, reply) -> { throw new AssertionError("admin setter reached"); },
+                (p, action) -> actions.add(action));
+        for (String action : List.of("accept", "decline", "stop")) {
+            command.onCommand(player, null, "heights", new String[] {"CaRrY", action.toUpperCase()});
+        }
+        assertEquals(List.of("accept", "decline", "stop"), actions);
+        for (String[] args : new String[][] {{"carry"}, {"carry", "throw"}, {"carry", "stop", "extra"},
+                {"player", "Steve", "0.5"}, {"settings"}}) {
+            command.onCommand(player, null, "heights", args);
+        }
+        command.onCommand(sender(true), null, "heights", new String[] {"carry", "accept"});
+        assertEquals(3, actions.size());
+        assertEquals(List.of("carry"), complete(player, ""));
+        assertEquals(List.of("accept", "decline", "stop"), complete(player, "carry", ""));
+        assertEquals(List.of("stop"), complete(player, "carry", "s"));
+        assertEquals(List.of(), complete(player, "player", ""));
+        org.bukkit.configuration.file.YamlConfiguration yaml = org.bukkit.configuration.file.YamlConfiguration
+                .loadConfiguration(new java.io.File("src/main/resources/plugin.yml"));
+        assertEquals(null, yaml.getString("commands.heights.permission"));
+        assertEquals("op", yaml.getString("permissions.spigotheights.admin.default"));
+    }
+
+    @Test
+    void runtimeHeightSetterCanPersistAsynchronouslyWithoutBypassingPermissions() {
+        List<java.util.function.Consumer<String>> replies = new ArrayList<>();
+        HeightsCommand async = new HeightsCommand(live, players, Logger.getAnonymousLogger(), (name, value, reply) -> {
+            assertEquals("Steve", name);
+            assertEquals(0.5, value);
+            replies.add(reply);
+        });
+        async.onCommand(sender(false), null, "heights", new String[] {"player", "Steve", "0.5"});
+        assertEquals(0, replies.size());
+        messages.clear();
+        async.onCommand(sender(true), null, "heights", new String[] {"player", "Steve", "0.5"});
+        assertEquals(1, replies.size());
+        assertEquals(List.of(), messages);
+        assertEquals(0.7, playerScale);
+        replies.getFirst().accept("Saved and active.");
+        assertEquals(List.of("Saved and active."), messages);
+    }
+
+    @Test
+    void viewsAndSetsOnlinePlayerWithNameAndSizeCompletion() {
+        CommandSender sender = sender(true);
+        command.onCommand(sender, null, "heights", new String[] {"player", "Steve"});
+        assertTrue(messages.getLast().contains("0.7"));
+        command.onCommand(sender, null, "heights", new String[] {"player", "steve", "0.5"});
+        assertEquals(0.5, playerScale);
+        assertEquals(0.5, playerStore.find(playerId));
+        assertTrue(messages.getLast().contains("Steve"));
+        assertEquals(List.of("player"), complete(sender, "pl"));
+        assertEquals(List.of("Steve"), complete(sender, "player", "st"));
+        assertTrue(complete(sender, "player", "Steve", "0.").contains("0.5"));
+        assertTrue(complete(sender, "player", "Steve", "1").contains("1.0"));
+        assertEquals(List.of(), complete(sender, "player", "Offline", ""));
+        assertEquals(List.of(), complete(sender, "player", "Steve", "0.5", ""));
+        for (String value : complete(sender, "player", "Steve", "")) {
+            assertTrue(players.isValid(Double.parseDouble(value)));
+        }
+    }
+
+    @Test
+    void invalidPlayerCommandsAndFailedSavesAreReportedWithoutResizing() throws Exception {
+        for (String[] args : new String[][] {
+                {"player"}, {"player", "Steve", "0.5", "extra"},
+                {"player", "Offline"}, {"player", "Ste", "0.5"},
+                {"player", "Steve", "nope"}, {"player", "Steve", "NaN"},
+                {"player", "Steve", "0.2"}, {"player", "Steve", "3.0"}}) {
+            int before = messages.size();
+            command.onCommand(sender(true), null, "heights", args);
+            assertEquals(before + 1, messages.size());
+            assertEquals(0.7, playerScale);
+            assertEquals(null, playerStore.find(playerId));
+        }
+        java.nio.file.Files.createDirectory(directory.resolve("state.yml.tmp"));
+        command.onCommand(sender(true), null, "heights", new String[] {"player", "Steve", "0.5"});
+        assertTrue(messages.getLast().contains("Could not save"));
+        assertEquals(0.7, playerScale);
+        assertEquals(null, playerStore.find(playerId));
+    }
+
+    @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"});
+        command.onCommand(sender, null, "heights", new String[] {"player", "Steve"});
+        command.onCommand(sender, null, "heights", new String[] {"player", "Steve", "0.5"});
+        assertEquals(0.7, playerScale);
+        assertEquals(null, playerStore.find(playerId));
+        assertEquals(List.of(), complete(sender, "player", ""));
+        assertEquals(List.of(), complete(sender, "player", "Steve", ""));
+        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, players, 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/PlayerHeightsTest.java

@@ -0,0 +1,78 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.UUID;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class PlayerHeightsTest {
+    @TempDir
+    Path directory;
+    private final UUID id = UUID.randomUUID();
+    private double scale = 0.7;
+    private LiveHeightSettings settings;
+    private HeightStore store;
+    private PlayerHeights heights;
+
+    @BeforeEach
+    void setup() {
+        settings = new LiveHeightSettings(new HeightSettings(0.4, 2.0, 0.1, 0.5, 1.5, 20), value -> {});
+        store = new HeightStore(directory.toFile());
+        heights = new PlayerHeights(settings, store, name -> name.equalsIgnoreCase("Steve")
+                ? new PlayerHeights.Target(id, "Steve", scale, scale * 2, value -> scale = value) : null,
+                () -> List.of("Steve"));
+    }
+
+    @Test
+    void viewsActualBaseAndEffectiveScaleAndPersistsChangesByUuid() throws Exception {
+        assertTrue(heights.describe("steve").contains("0.7"));
+        assertTrue(heights.describe("Steve").contains("1.4"));
+        heights.set("STEVE", 0.5);
+        assertEquals(0.5, scale);
+        HeightStore reloaded = new HeightStore(directory.toFile());
+        assertEquals(0.5, reloaded.find(id));
+        assertEquals(0.5, HeightMath.safeStoredScale(reloaded.find(id), settings.get()));
+        assertEquals(List.of("Steve"), heights.names());
+    }
+
+    @Test
+    void rejectsUnknownPlayersAndInvalidScalesWithoutChangingState() {
+        assertThrows(IllegalArgumentException.class, () -> heights.describe("Ste"));
+        assertThrows(IllegalArgumentException.class, () -> heights.set("Offline", 0.5));
+        for (double value : new double[] {Double.NaN, Double.POSITIVE_INFINITY, -1, 0.2, 3.0}) {
+            assertThrows(IllegalArgumentException.class, () -> heights.set("Steve", value));
+        }
+        assertEquals(0.7, scale);
+        assertEquals(null, store.find(id));
+    }
+
+    @Test
+    void usesLiveLimitsAndAllowsRestorationOutsideThem() throws Exception {
+        settings.setBound("max", 0.8);
+        heights.set("Steve", 1.0);
+        assertEquals(1.0, scale);
+        assertEquals(1.0, HeightMath.safeStoredScale(new HeightStore(directory.toFile()).find(id), settings.get()));
+        assertThrows(IllegalArgumentException.class, () -> heights.set("Steve", 0.9));
+        settings.setBound("min", 0.2);
+        heights.set("Steve", 0.2);
+        assertEquals(0.2, scale);
+    }
+
+    @Test
+    void failedSaveLeavesLiveAndCachedHeightUnchanged() throws Exception {
+        store.save(id, scale);
+        Files.createDirectory(directory.resolve("state.yml.tmp"));
+        assertThrows(IOException.class, () -> heights.set("Steve", 0.5));
+        assertEquals(0.7, scale);
+        assertEquals(0.7, store.find(id));
+        assertEquals(0.7, new HeightStore(directory.toFile()).find(id));
+    }
+}

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

@@ -4,9 +4,72 @@ import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import static org.junit.jupiter.api.Assertions.assertNull;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.persistence.PersistentDataType;
 import org.junit.jupiter.api.Test;
 
 class PotionRecipesTest {
+    private final NamespacedKey key = new NamespacedKey("spigotheights", "stature_potion");
+    private final PotionRecipes potions = new PotionRecipes(null, key, BukkitDoubles.Item::new);
+
+    @Test
+    void authenticatesAllFormsByTypedMetadataNotDisplayName() {
+        for (StaturePotion kind : StaturePotion.values()) {
+            for (Material form : new Material[] {Material.POTION, Material.SPLASH_POTION, Material.LINGERING_POTION}) {
+                BukkitDoubles.Item item = new BukkitDoubles.Item(form);
+                item.getItemMeta().displayName(net.kyori.adventure.text.Component.text(kind.displayName()));
+                assertNull(potions.identify(item));
+                item.getItemMeta().getPersistentDataContainer().set(key, PersistentDataType.INTEGER, 1);
+                assertNull(potions.identify(item));
+                item.getItemMeta().getPersistentDataContainer().set(key, PersistentDataType.STRING, "UNKNOWN");
+                assertNull(potions.identify(item));
+                item.getItemMeta().getPersistentDataContainer().set(key, PersistentDataType.STRING, kind.name());
+                assertEquals(kind, potions.identify(item));
+            }
+            BukkitDoubles.Item fake = new BukkitDoubles.Item(Material.STONE);
+            fake.getItemMeta().getPersistentDataContainer().set(key, PersistentDataType.STRING, kind.name());
+            assertNull(potions.identify(fake));
+        }
+        assertNull(potions.identify(null));
+    }
+
+    @Test
+    void registersEightScopedBrewingConversionsWithAuthenticatedResults() {
+        java.util.List<io.papermc.paper.potion.PotionMix> mixes = new java.util.ArrayList<>();
+        java.util.List<NamespacedKey> removed = new java.util.ArrayList<>();
+        org.bukkit.potion.PotionBrewer brewer = BukkitDoubles.proxy(org.bukkit.potion.PotionBrewer.class,
+                (proxy, method, args) -> {
+                    switch (method.getName()) {
+                        case "addPotionMix" -> mixes.add((io.papermc.paper.potion.PotionMix) args[0]);
+                        case "removePotionMix" -> removed.add((NamespacedKey) args[0]);
+                        default -> throw new UnsupportedOperationException(method.getName());
+                    }
+                    return null;
+                });
+        potions.registerBrewing(brewer);
+        assertEquals(8, mixes.size());
+        assertEquals(8, mixes.stream().map(io.papermc.paper.potion.PotionMix::getKey).distinct().count());
+        assertEquals(mixes.stream().map(io.papermc.paper.potion.PotionMix::getKey).toList(), removed);
+        for (var mix : mixes) {
+            Material target = mix.getResult().getType();
+            boolean splash = target == Material.SPLASH_POTION;
+            assertEquals(splash ? Material.SPLASH_POTION : Material.LINGERING_POTION, target);
+            StaturePotion kind = potions.identify(mix.getResult());
+            org.junit.jupiter.api.Assertions.assertNotNull(kind);
+            Material source = splash ? Material.POTION : Material.SPLASH_POTION;
+            BukkitDoubles.Item input = new BukkitDoubles.Item(source);
+            org.junit.jupiter.api.Assertions.assertFalse(mix.getInput().test(input));
+            input.getItemMeta().getPersistentDataContainer().set(key, PersistentDataType.STRING, kind.name());
+            org.junit.jupiter.api.Assertions.assertTrue(mix.getInput().test(input));
+            org.junit.jupiter.api.Assertions.assertFalse(mix.getInput().test(mix.getResult()));
+            org.junit.jupiter.api.Assertions.assertTrue(mix.getIngredient().test(new BukkitDoubles.Item(
+                    splash ? Material.GUNPOWDER : Material.DRAGON_BREATH)));
+            org.junit.jupiter.api.Assertions.assertFalse(mix.getIngredient().test(new BukkitDoubles.Item(Material.SUGAR)));
+        }
+    }
+
     @Test
     void recipesUseApprovedShapes() {
         assertArrayEquals(new String[] {"ACA", "AWA", "ACA"}, PotionRecipes.SHIFTING_SHAPE);

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));
+    }
+}

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

@@ -0,0 +1,36 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Server;
+import org.bukkit.entity.ThrownPotion;
+import org.bukkit.event.entity.EntityRemoveEvent;
+import org.junit.jupiter.api.Test;
+
+class StatureCloudsTest {
+    @Test
+    void unloadRetainsDurableReceiptsButPermanentSourceRemovalRetiresThem() {
+        PotionRecipes potions = new PotionRecipes(null, new NamespacedKey("spigotheights", "stature_potion"),
+                BukkitDoubles.Item::new);
+        ThrowableStatureListener listener = new ThrowableStatureListener(potions,
+                new NamespacedKey("spigotheights", "cloud_kind"), (source, player, kind, done) -> {});
+        Server server = BukkitDoubles.proxy(Server.class, (proxy, method, args) -> {
+            if (method.getName().equals("getWorlds")) { return List.of(); }
+            throw new UnsupportedOperationException(method.getName());
+        });
+        List<UUID> retired = new ArrayList<>();
+        StatureClouds clouds = new StatureClouds(server, listener, retired::add);
+        ThrownPotion source = ThrowableStatureListenerTest.entity(ThrownPotion.class,
+                potions.create(StaturePotion.GROWTH, Material.SPLASH_POTION));
+        clouds.onRemove(new EntityRemoveEvent(source, EntityRemoveEvent.Cause.UNLOAD));
+        clouds.onRemove(new EntityRemoveEvent(ThrowableStatureListenerTest.entity(ThrownPotion.class,
+                new BukkitDoubles.Item(Material.SPLASH_POTION)), EntityRemoveEvent.Cause.HIT));
+        assertEquals(List.of(), retired);
+        clouds.onRemove(new EntityRemoveEvent(source, EntityRemoveEvent.Cause.HIT));
+        assertEquals(List.of(source.getUniqueId()), retired);
+    }
+}

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

@@ -0,0 +1,32 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.util.ArrayList;
+import java.util.List;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.entity.Player;
+import org.bukkit.event.player.PlayerItemConsumeEvent;
+import org.bukkit.inventory.EquipmentSlot;
+import org.junit.jupiter.api.Test;
+
+class StatureListenerTest {
+    @Test
+    void onlyUncancelledAuthenticatedDrinkableItemsReachPermanentService() {
+        PotionRecipes potions = new PotionRecipes(null, new NamespacedKey("spigotheights", "stature_potion"),
+                BukkitDoubles.Item::new);
+        List<StaturePotion> drinks = new ArrayList<>();
+        StatureListener listener = new StatureListener(potions, (player, kind) -> drinks.add(kind), player -> {}, Runnable::run);
+        Player player = ThrowableStatureListenerTest.entity(Player.class, null);
+        var cancelled = new PlayerItemConsumeEvent(player, potions.create(StaturePotion.GROWTH), EquipmentSlot.HAND);
+        cancelled.setCancelled(true);
+        listener.onConsume(cancelled);
+        listener.onConsume(new PlayerItemConsumeEvent(player,
+                potions.create(StaturePotion.GROWTH, Material.SPLASH_POTION), EquipmentSlot.HAND));
+        listener.onConsume(new PlayerItemConsumeEvent(player, new BukkitDoubles.Item(Material.POTION), EquipmentSlot.HAND));
+        assertEquals(List.of(), drinks);
+        cancelled.setCancelled(false);
+        listener.onConsume(cancelled);
+        assertEquals(List.of(StaturePotion.GROWTH), drinks);
+    }
+}

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

@@ -0,0 +1,68 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class StatureQueueTest {
+    @Test
+    void capturesNextOperationOnlyAfterDurableCompletionAndNeverWritesOnMain() {
+        ArrayDeque<Runnable> worker = new ArrayDeque<>();
+        ArrayDeque<Runnable> main = new ArrayDeque<>();
+        List<String> events = new ArrayList<>();
+        double[] scale = {1.0};
+        StatureQueue queue = new StatureQueue(worker::add, main::add);
+        for (int i = 0; i < 2; i++) {
+            queue.submit(() -> {
+                events.add("capture");
+                double next = scale[0] - 0.2;
+                return () -> { events.add("save"); return next; };
+            }, (result, error) -> { assertNull(error); events.add("apply"); scale[0] = result; });
+        }
+        assertEquals(List.of("capture"), events);
+        assertEquals(1.0, scale[0]);
+        worker.removeFirst().run();
+        assertEquals(List.of("capture", "save"), events);
+        assertEquals(1.0, scale[0]);
+        main.removeFirst().run();
+        assertEquals(List.of("capture", "save", "apply", "capture"), events);
+        worker.removeFirst().run(); main.removeFirst().run();
+        assertEquals(0.6, scale[0], 0.00001);
+    }
+
+    @Test
+    void shutdownRejectsPendingAndNewOperationsButAllowsInflightSaveToFinish() {
+        ArrayDeque<Runnable> worker = new ArrayDeque<>();
+        ArrayDeque<Runnable> main = new ArrayDeque<>();
+        List<Exception> failures = new ArrayList<>();
+        StatureQueue queue = new StatureQueue(worker::add, main::add);
+        queue.submit(() -> () -> 0.8, (result, error) -> assertNull(error));
+        queue.submit(() -> () -> 0.6, (result, error) -> failures.add(error));
+        queue.close();
+        queue.submit(() -> () -> 0.4, (result, error) -> failures.add(error));
+        assertEquals(2, failures.size());
+        failures.forEach(org.junit.jupiter.api.Assertions::assertNotNull);
+        worker.removeFirst().run(); main.removeFirst().run();
+        assertEquals(0, worker.size());
+    }
+
+    @Test
+    void failedPersistenceReportsFailureAndDoesNotStrandNextOperation() {
+        ArrayDeque<Runnable> worker = new ArrayDeque<>();
+        ArrayDeque<Runnable> main = new ArrayDeque<>();
+        List<Double> applied = new ArrayList<>();
+        StatureQueue queue = new StatureQueue(worker::add, main::add);
+        queue.submit(() -> () -> { throw new java.io.IOException("disk failure"); },
+                (result, error) -> { assertNull(result); assertNotNull(error); });
+        queue.submit(() -> () -> 1.4, (result, error) -> { assertNull(error); applied.add(result); });
+        assertEquals(1, worker.size());
+        worker.removeFirst().run(); main.removeFirst().run();
+        worker.removeFirst().run(); main.removeFirst().run();
+        assertEquals(List.of(1.4), applied);
+    }
+}

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

@@ -0,0 +1,127 @@
+package games.dmg.spigotheights;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.nio.file.Files;
+
+import java.nio.file.Path;
+import java.time.Instant;
+import java.util.UUID;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class TemporaryStatureTest {
+    @TempDir Path directory;
+    private final UUID player = UUID.randomUUID();
+    private final HeightSettings settings = new HeightSettings(0.2, 3.0, 0.2, 0.5, 1.5, 20);
+    private final Instant start = Instant.parse("2026-01-01T00:00:00Z");
+
+    @Test
+    void applicationAfterExpiryStartsFromRestoredBaselineNotStaleTemporaryScale() throws Exception {
+        TemporaryStature stature = new TemporaryStature(new HeightStore(directory.toFile()));
+        stature.apply(player, 1.0, StaturePotion.DIMINUTION, settings, start, bound -> 0);
+        assertEquals(1.2, stature.apply(player, 0.8, StaturePotion.GROWTH, settings,
+                start.plusSeconds(300), bound -> 0));
+        assertEquals(1.0, stature.resume(player, settings, start.plusSeconds(600)));
+    }
+
+    @Test
+    void durableCloudReceiptPreventsDuplicateAfterUnloadReloadAndPermanentOverride() throws Exception {
+        UUID source = UUID.randomUUID();
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        assertEquals(0.8, stature.applyOnce(player, source, 1.0, StaturePotion.DIMINUTION, settings, start, bound -> 0));
+        store.save(player, 1.4);
+        HeightStore reloaded = new HeightStore(directory.toFile());
+        assertNull(new TemporaryStature(reloaded).applyOnce(player, source, 1.4, StaturePotion.DIMINUTION,
+                settings, start.plusSeconds(10), bound -> 0));
+        assertEquals(1.4, reloaded.find(player));
+        assertNull(reloaded.sequence(player));
+    }
+
+    @Test
+    void unobservedExpirySurvivesDisconnectBetweenSaveAndLiveApplication() throws Exception {
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        stature.apply(player, 2.0, StaturePotion.DIMINUTION, settings, start, bound -> 0);
+        HeightSettings smaller = new HeightSettings(0.2, 0.8, 0.2, 0.5, 1.5, 20);
+        assertEquals(2.0, stature.resume(player, smaller, start.plusSeconds(300)));
+        // Player disconnected before observing the result: login must still restore exactly.
+        assertEquals(2.0, new TemporaryStature(new HeightStore(directory.toFile()))
+                .resume(player, smaller, start.plusSeconds(301)));
+    }
+
+    @Test
+    void reloadCountsOfflineTimeAndRestoresExactBaselineOutsideChangedLimits() throws Exception {
+        TemporaryStature stature = new TemporaryStature(new HeightStore(directory.toFile()));
+        stature.apply(player, 2.0, StaturePotion.DIMINUTION, settings, start, bound -> 0);
+        HeightStore reloaded = new HeightStore(directory.toFile());
+        TemporaryStature restarted = new TemporaryStature(reloaded);
+        HeightSettings smaller = new HeightSettings(0.2, 0.8, 0.2, 0.5, 1.5, 20);
+        assertEquals(2.0, restarted.resume(player, smaller, start.plusSeconds(301)));
+        restarted.acknowledgeRestoration(player, reloaded.sequence(player));
+        assertNull(reloaded.sequence(player));
+        // Only processing the expiry bypasses new limits; later ordinary joins use them.
+        assertEquals(0.8, restarted.resume(player, smaller, start.plusSeconds(302)));
+    }
+
+    @Test
+    void permanentSaveEndsSequenceAndFailedSavePreservesIt() throws Exception {
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        stature.apply(player, 1.0, StaturePotion.DIMINUTION, settings, start, bound -> 0);
+        Files.createDirectory(directory.resolve("state.yml.tmp"));
+        assertThrows(IOException.class, () -> store.save(player, 1.4));
+        assertEquals(0.8, store.find(player));
+        assertEquals(1.0, store.sequence(player).baseline());
+        Files.delete(directory.resolve("state.yml.tmp"));
+        store.save(player, 1.4);
+        assertNull(new HeightStore(directory.toFile()).sequence(player));
+        assertEquals(1.4, stature.resume(player, settings, start.plusSeconds(600)));
+    }
+
+    @Test
+    void permanentDrinkUsesCurrentSizeAndEndsSequenceIncludingAtExpiryBoundary() throws Exception {
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        stature.apply(player, 1.0, StaturePotion.DIMINUTION, settings, start, bound -> 0);
+        assertEquals(0.6, stature.drink(player, 0.8, StaturePotion.DIMINUTION, settings,
+                start.plusSeconds(1), bound -> 0));
+        assertNull(store.sequence(player));
+        assertEquals(0.6, stature.resume(player, settings, start.plusSeconds(600)));
+        stature.apply(player, 0.6, StaturePotion.GROWTH, settings, start, bound -> 0);
+        assertEquals(0.4, stature.drink(player, 0.8, StaturePotion.DIMINUTION, settings,
+                start.plusSeconds(300), bound -> 0));
+        assertNull(store.sequence(player));
+    }
+
+    @Test
+    void allKindsRespectBoundsRestorationAndTimerRefreshEvenAtBounds() throws Exception {
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        assertEquals(0.2, stature.apply(player, 0.2, StaturePotion.DIMINUTION, settings, start, bound -> 0));
+        assertEquals(3.0, stature.apply(player, 0.2, StaturePotion.SHIFTING, settings,
+                start.plusSeconds(10), bound -> bound - 1));
+        assertEquals(3.0, stature.apply(player, 3.0, StaturePotion.GROWTH, settings,
+                start.plusSeconds(20), bound -> 0));
+        assertEquals(start.plusSeconds(320), store.sequence(player).expiresAt());
+        assertEquals(1.0, stature.apply(player, 3.0, StaturePotion.RESTORATION, settings,
+                start.plusSeconds(30), bound -> 0));
+        assertEquals(0.2, stature.resume(player, settings, start.plusSeconds(330)));
+    }
+
+    @Test
+    void chainedEffectsRestoreFirstBaselineFiveMinutesAfterLastApplication() throws Exception {
+        HeightStore store = new HeightStore(directory.toFile());
+        TemporaryStature stature = new TemporaryStature(store);
+        assertEquals(0.8, stature.apply(player, 1.0, StaturePotion.DIMINUTION, settings, start, bound -> 0));
+        assertEquals(0.6, stature.apply(player, 0.8, StaturePotion.DIMINUTION, settings,
+                start.plusSeconds(240), bound -> 0));
+        assertEquals(0.6, stature.resume(player, settings, start.plusSeconds(539)));
+        assertEquals(1.0, stature.resume(player, settings, start.plusSeconds(540)));
+        assertEquals(1.0, store.find(player));
+    }
+}

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

@@ -0,0 +1,161 @@
+package games.dmg.spigotheights;
+
+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.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+import java.util.function.Consumer;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.entity.AreaEffectCloud;
+import org.bukkit.entity.LivingEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.entity.ThrownPotion;
+import org.bukkit.event.entity.AreaEffectCloudApplyEvent;
+import org.bukkit.event.entity.LingeringPotionSplashEvent;
+import org.bukkit.event.entity.PotionSplashEvent;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.persistence.PersistentDataContainer;
+import org.junit.jupiter.api.Test;
+
+class ThrowableStatureListenerTest {
+    private final PotionRecipes potions = new PotionRecipes(null,
+            new NamespacedKey("spigotheights", "stature_potion"), BukkitDoubles.Item::new);
+    private final List<StaturePotion> applied = new ArrayList<>();
+    private final List<Consumer<Boolean>> pending = new ArrayList<>();
+    private boolean asynchronous;
+    private final ThrowableStatureListener listener = new ThrowableStatureListener(potions,
+            new NamespacedKey("spigotheights", "cloud_kind"), (source, player, kind, done) -> {
+                applied.add(kind);
+                if (asynchronous) { pending.add(done); } else { done.accept(true); }
+            });
+
+    @Test
+    void splashUsesAuthenticatedItemPositiveIntensityAndOncePerPlayer() {
+        Player player = entity(Player.class, null);
+        Player missed = entity(Player.class, null);
+        LivingEntity mob = entity(LivingEntity.class, null);
+        ThrownPotion thrown = entity(ThrownPotion.class, potions.create(StaturePotion.DIMINUTION, Material.SPLASH_POTION));
+        Map<LivingEntity, Double> recipients = new HashMap<>();
+        recipients.put(player, 0.1); recipients.put(missed, 0.0); recipients.put(mob, 1.0);
+        PotionSplashEvent event = new PotionSplashEvent(thrown, null, null, null, recipients);
+        event.setCancelled(true);
+        listener.onSplash(event);
+        assertEquals(List.of(), applied);
+        event.setCancelled(false);
+        listener.onSplash(event);
+        listener.onSplash(event);
+        assertEquals(List.of(StaturePotion.DIMINUTION), applied);
+        ThrownPotion ordinary = entity(ThrownPotion.class, new BukkitDoubles.Item(Material.SPLASH_POTION));
+        listener.onSplash(new PotionSplashEvent(ordinary, null, null, null, recipients));
+        assertEquals(1, applied.size());
+    }
+
+    @Test
+    void cloudRequiresUncancelledAuthenticatedCreationAndAppliesOnlyOncePerPlayer() {
+        Player player = entity(Player.class, null);
+        AreaEffectCloud cloud = entity(AreaEffectCloud.class, null);
+        var application = new AreaEffectCloudApplyEvent(cloud, new ArrayList<>(List.of(player)));
+        listener.onCloud(application);
+        assertEquals(0, applied.size());
+        var creation = new LingeringPotionSplashEvent(entity(ThrownPotion.class,
+                potions.create(StaturePotion.GROWTH, Material.LINGERING_POTION)), null, null, null, cloud);
+        creation.setCancelled(true);
+        listener.onLingering(creation);
+        assertFalse(creation.allowsEmptyCreation());
+        listener.onCloud(application);
+        assertEquals(0, applied.size());
+        creation.setCancelled(false);
+        listener.onLingering(creation);
+        assertTrue(creation.allowsEmptyCreation());
+        application.setCancelled(true);
+        listener.onCloud(application);
+        assertEquals(0, applied.size());
+        application.setCancelled(false);
+        asynchronous = true;
+        listener.onCloud(application);
+        listener.onCloud(application);
+        assertEquals(List.of(StaturePotion.GROWTH), applied);
+        assertFalse(cloud.getPersistentDataContainer().has(new NamespacedKey("spigotheights",
+                "hit_" + player.getUniqueId())), "Pending reservations must not be serialized on unload");
+        pending.removeFirst().accept(false);
+        listener.onCloud(application);
+        assertEquals(2, applied.size());
+        pending.removeFirst().accept(true);
+        listener.onCloud(application);
+        assertEquals(2, applied.size());
+        // Receipts are cloud-owned metadata, not player-object or listener-instance identity.
+        new ThrowableStatureListener(potions, new NamespacedKey("spigotheights", "cloud_kind"),
+                (source, recipient, kind, done) -> { throw new AssertionError("duplicate after listener restart"); })
+                .onCloud(application);
+    }
+
+    @Test
+    void effectlessCloudTickDispatchesCancellableEventAndHonorsWaitAndRadius() {
+        Player inside = locatedPlayer(1.0, 0.0);
+        Player outsideCircle = locatedPlayer(2.0, 2.0);
+        PersistentDataContainer data = BukkitDoubles.container();
+        int[] age = {9};
+        UUID cloudId = UUID.randomUUID();
+        AreaEffectCloud cloud = BukkitDoubles.proxy(AreaEffectCloud.class, (proxy, method, args) -> switch (method.getName()) {
+            case "getPersistentDataContainer" -> data;
+            case "isValid" -> true;
+            case "getUniqueId" -> cloudId;
+            case "getTicksLived" -> age[0];
+            case "getWaitTime" -> 10;
+            case "getRadius" -> 2.0f;
+            case "getLocation" -> new org.bukkit.Location(null, 0, 0, 0);
+            case "getBoundingBox" -> new org.bukkit.util.BoundingBox(-2, 0, -2, 2, 0.5, 2);
+            case "getNearbyEntities" -> List.of(inside, outsideCircle);
+            default -> throw new UnsupportedOperationException(method.getName());
+        });
+        listener.onLingering(new LingeringPotionSplashEvent(entity(ThrownPotion.class,
+                potions.create(StaturePotion.RESTORATION, Material.LINGERING_POTION)), null, null, null, cloud));
+        List<AreaEffectCloudApplyEvent> dispatched = new ArrayList<>();
+        Consumer<AreaEffectCloudApplyEvent> cancel = event -> {
+            dispatched.add(event); event.setCancelled(true); listener.onCloud(event);
+        };
+        listener.tickCloud(cloud, cancel);
+        assertEquals(0, dispatched.size());
+        age[0] = 10;
+        listener.tickCloud(cloud, cancel);
+        assertEquals(1, dispatched.size());
+        assertEquals(List.of(inside), dispatched.getFirst().getAffectedEntities());
+        assertEquals(0, applied.size());
+        listener.tickCloud(cloud, listener::onCloud);
+        listener.tickCloud(cloud, listener::onCloud);
+        assertEquals(List.of(StaturePotion.RESTORATION), applied);
+    }
+
+    private static Player locatedPlayer(double x, double z) {
+        Player delegate = entity(Player.class, null);
+        return BukkitDoubles.proxy(Player.class, (proxy, method, args) -> switch (method.getName()) {
+            case "getLocation" -> new org.bukkit.Location(null, x, 0, z);
+            case "getBoundingBox" -> new org.bukkit.util.BoundingBox(x - 0.2, 0, z - 0.2, x + 0.2, 1.8, z + 0.2);
+            case "getGameMode" -> org.bukkit.GameMode.SURVIVAL;
+            case "equals" -> proxy == args[0];
+            default -> method.invoke(delegate, args);
+        });
+    }
+
+    static <T> T entity(Class<T> type, ItemStack item) {
+        UUID id = UUID.randomUUID();
+        PersistentDataContainer data = BukkitDoubles.container();
+        return BukkitDoubles.proxy(type, (proxy, method, args) -> switch (method.getName()) {
+            case "getUniqueId" -> id;
+            case "getPersistentDataContainer" -> data;
+            case "getItem" -> item;
+            case "isOnline", "isValid" -> true;
+            case "isDead" -> false;
+            case "hashCode" -> id.hashCode();
+            case "equals" -> proxy == args[0];
+            case "toString" -> id.toString();
+            default -> throw new UnsupportedOperationException(method.getName());
+        });
+    }
+}