Add dynamic_lights 1.0.0

Submitted by @CayMac97 through the form.

Co-authored-by: CayMac97 <[email protected]>

README.md

@@ -65,7 +65,7 @@ why.
 | `.github/workflows/publish.yml` | On merge: releases, then `index.json` on Pages |
 | `.github/workflows/cleanup.yml` | Weekly: staging files nobody needs any more |
 | `.github/workflows/native.yml` | Horizon's native mods: each changed one's tests, `.hnmod` and game check, all of them together, and weekly on the newest Nightly |
-| `native/<name>/` | Horizon's own native mods (Zoom, FPS Counter, Keystrokes, Minimap, Recipes): the source of their `.hnmod` files |
+| `native/<name>/` | Horizon's own native mods (Zoom, FPS Counter, Keystrokes, Minimap, Recipes, Coordinates HUD): the source of their `.hnmod` files |
 | `native/tools/` | Shared by them: apply on Horizon, check, build, package, prove (`native/tools/native.py`) |
 | `scripts/` | What the workflows share |
 

mods/appleskin.toml

@@ -0,0 +1,45 @@
+id = "appleskin"
+kind = "native-mod"
+name = "AppleSkin"
+summary = "Shows how much HP, hunger, and saturation will be restored."
+description = """
+AppleSkin for Horizon, a native mod.
+
+Renders saturation, exhaustion, and held-food values over the hunger bar, as the original AppleSkin does.
+
+Based on AppleSkin by squeek502. See the LICENSE in the source for the
+original copyright and licence notices."""
+authors = ["soufi"]
+owners = ["soufied"]
+license = "MIT"
+source = "https://github.com/soufied/AppleSkin-Horizon"
+icon = "icons/appleskin.png"
+key = "RWT6eNq4e5WfVDA2lzOOi6XCm/+jJgilqT1+HUUM33ie5MCjcRfSg760"
+
+[[versions]]
+version = "0.1.1"
+published = "2026-10-31"
+game = "26.3"
+file = "appleskin-0.1.1.hnmod"
+sha256 = "182117d2a9767bc22a7c6652efd24551990cea015193784f20aeb8a7ba35b4ac"
+signature = """
+untrusted comment: signature from minisign secret key
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+trusted comment: timestamp:1793418678\tfile:appleskin-0.1.1.hnmod\thashed
+gK9BQoCtM8sRPSvSiBzAT2IE8nZlCDfUa7tWCG7cG/v7H41E+4DnflE0KtAPdqi/9+MQT3ONmT4qbGFVio58BA=="""
+changelog = """
+dumped to 0.1.1
+added icon"""
+
+[[versions]]
+version = "1.0.0"
+published = "2026-10-30"
+game = "26.3"
+file = "appleskin-1.0.0.hnmod"
+sha256 = "3c25b916f74f47faf40070a8654c546d15cb79ac3947f140e257f4cb041aeb96"
+signature = """
+untrusted comment: signature from minisign secret key
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+trusted comment: timestamp:1793368049\tfile:appleskin-1.0.0.hnmod\thashed
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+changelog = "First release. AppleSkin for Horizon as a native mod: saturation, exhaustion and the food in your hand, drawn over the food bar."

mods/biomecompass.toml

@@ -16,7 +16,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/biomecompass"
-icon = "https://raw.githubusercontent.com/d3grando/biomecompass/main/icon.png"
+icon = "icons/biomecompass.png"
 
 [[versions]]
 version = "0.2.2"

mods/blockscope.toml

@@ -1,5 +1,5 @@
 id = "blockscope"
-kind = "mod"
+kind = "native-mod"
 name = "Blockscope"
 summary = "The block under your crosshair: its name, id, distance and icon, with reach, placement and opacity on its own settings page. A Jade-style tooltip for Horizon."
 description = "Jade-style block info for Horizon: the block under your crosshair, its name in your language, its block id, how far it is and its icon."
@@ -7,7 +7,15 @@ authors = ["Domanffe"]
 owners = ["Domanffe"]
 license = "MIT"
 source = "https://github.com/Domanffe/blockscope"
-icon = "https://raw.githubusercontent.com/Domanffe/blockscope/main/docs/icon.png"
+icon = "https://horizon-rust.github.io/horizon-mods/icons/blockscope.png"
+
+[[versions]]
+version = "0.3.0"
+published = "2026-10-30"
+game = "26.3"
+file = "blockscope-0.3.0.hnmod"
+sha256 = "ba4a1c887ab26a2a9189c671cbdbea3ce2ed212a6e3d32f1fffaa60386198358"
+changelog = "Native: the WebAssembly mod rewritten as a mixin bundle for the launcher's native mods, with hardness and the tool's icon, block states, crop growth, a container's slots and a creature's health, each on its own switch. Its settings carry over from 0.2.0."
 
 [[versions]]
 version = "0.2.0"

mods/carryblock.toml

@@ -17,7 +17,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/carryblock"
-icon = "https://raw.githubusercontent.com/d3grando/carryblock/main/icon.png"
+icon = "icons/carryblock.png"
 
 [[versions]]
 version = "0.1.2"

mods/chatheads.toml

@@ -0,0 +1,23 @@
+id = "chatheads"
+kind = "native-mod"
+name = "ChatHeads"
+summary = "A player's head left of every chat line they wrote."
+description = """
+Each chat line from a player gets their 8x8 skin face in the strip to its left, like the Chat Heads Java mod. Lines without a player (system messages, /me, wrapped continuations) stay as they are; the face fades with its line.
+
+Settings: Options > Mods > ChatHeads > Settings (on or off).
+
+Known limit: the chat's hit-test does not know about the 10 px indent, so clicking a link in chat lands 10 px left of its pixels."""
+authors = ["Domanffe"]
+owners = ["Domanffe"]
+license = "MIT"
+source = "https://github.com/Domanffe/chatheads"
+icon = "https://horizon-rust.github.io/horizon-mods/icons/chatheads.png"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "chatheads-0.1.0.hnmod"
+sha256 = "c20605c24e29a762b9aea85cba1b0cc7955955a40a031efae70a5b01e4e79df4"
+changelog = "First release: a native mod for Horizon 26.3. Every chat line from a player gets their 8x8 skin face in the strip to its left; system lines, /me and wrapped continuations get none. Settings in Options > Mods."

mods/classic_zoom.toml

@@ -1,5 +1,5 @@
 id = "classic_zoom"
-kind = "mod"
+kind = "native-mod"
 name = "Classic Zoom"
 summary = "Hold V to zoom 3x, scroll for more, release to snap back. Instant, no settings, inspired by WI Zoom."
 description = """
@@ -32,14 +32,29 @@ Both can be installed at once: they use different keys.
 - Written from scratch for Horizon's mod API. Not affiliated with Wurst-Imperium.
 - Some servers forbid zoom mods: check the rules before you join.
 
+**Now a native mod (2.0.0)**: the launcher builds it into the game (Settings → Game → Native mods (experimental), then Build). Native mods are not sandboxed and run with your account's permissions, so read the source before you build it: it is one small bundle on Horizon's native hook points (key, wheel, zoom, mods list). Tested against Horizon `6f8c7a0e5d531d3834c4d0be4659a1db8e7e5c2a` with Horizon Mixins `0d6b103c70633d8fd9443d8d0acd3aadaacedb06`. A key set in 1.0.0 carries over. 1.0.0 is the WebAssembly version.
+
 Source and issues: [github.com/SU4G3/classic-zoom](https://github.com/SU4G3/classic-zoom)"""
 authors = ["Surge"]
 owners = ["SU4G3"]
 license = "GPL-3.0-or-later"
 source = "https://github.com/SU4G3/classic-zoom"
-icon = "https://github.com/SU4G3/classic-zoom/blob/main/.github/icon.png?raw=true"
+icon = "icons/classic_zoom.png"
 key = "RWTOxMcIG6MtC0QQnhWEMC+nLKJ6+u4trV/rF+4juSRuow8W4b5P+CPS"
 
+[[versions]]
+version = "2.0.0"
+published = "2026-10-29"
+game = "26.3"
+file = "classic_zoom-2.0.0.hnmod"
+sha256 = "a8bdeba615ed31b9bd10280fcf8ba04a31935bc65fff429fc0e83d1c8090dac9"
+signature = """
+untrusted comment: signature from minisign secret key
+RUTOxMcIG6MtCyXVhFrgrbWwg3pEBeR8iQ6g3w8MlWbzunH02kAF3swud3hq59EQvuoNpQxj7eTNRy6IJ4l+++7H1EazgGLV3AY=
+trusted comment: timestamp:1793286240\tfile:classic_zoom-2.0.0.hnmod\thashed
+bbYFmm0wap7Mgnt+wxSMkC/FqklbuAZage02x4Kt5Mi2mzknFbhWij/6sOx5ojRAquDT1XLRpRd2UrrAy4x4Bg=="""
+changelog = "Now a native mod (WebAssembly code mods are going away). Same zoom: V by default, 3x, x1.1 per wheel step within 1x-10x, instant, slower turning while zoomed; a key set in 1.0.0 carries over. Pinned to Horizon 6f8c7a0 and Horizon Mixins 0d6b103."
+
 [[versions]]
 version = "1.0.0"
 published = "2026-10-29"

mods/coords_hud.toml

@@ -1,22 +1,35 @@
 id = "coords_hud"
-kind = "mod"
+kind = "native-mod"
 name = "Coordinates HUD"
-summary = "Your coordinates, facing and the time of day in a corner of the screen."
+summary = "Your coordinates and facing in a corner of the screen."
 description = """
-The SDK's example mod. It draws your block position, the direction you face and the time of day
-in the top-left corner, every frame.
+Your block position and the direction you face in the top-left corner of the screen.
 
 - `/where` puts your coordinates and dimension in chat.
-- `/coords` hides or shows the panel.
+- `/coords` hides or shows the box, and the game keeps your choice (also Options > Mods > Coordinates HUD > Settings).
 
-It reads the game (position, health, time), draws on the HUD and writes to chat: nothing else.
+It reads the player's position, draws on the HUD and writes to chat: nothing else.
+
+Now a native mod (2.0.0): built into the game by the launcher, on the Horizon you play, like any native mod
+(Settings → Game → Native mods (experimental), then Build). It was the WebAssembly SDK's example mod; the time of
+day line is gone, since Horizon's hook points don't give the game's clock yet. Turn it off in Options > Mods: it
+rests at once, and the next build leaves it out. Its source is
+[horizon-mods/native/coords-hud](https://github.com/horizon-rust/horizon-mods/tree/main/native/coords-hud).
 """
 authors = ["Horizon"]
 owners = ["ludovic111"]
 license = "MIT"
-source = "https://github.com/horizon-rust/horizon/tree/main/crates/horizon-mod-sdk/examples/coords-hud"
+source = "https://github.com/horizon-rust/horizon-mods/tree/main/native/coords-hud"
 icon = "icons/coords_hud.png"
 
+[[versions]]
+version = "2.0.0"
+published = "2026-10-29"
+game = "26.3"
+file = "coords_hud-2.0.0.hnmod"
+sha256 = "432376fad3062b3517e274d3b8c0d0b52fc5d6de2aee20a0b340c8cab5a8cf08"
+changelog = "Native: built into the game by the launcher on Horizon's native hook points; /coords is kept; turn it off in Options > Mods. The time of day line is gone for now."
+
 [[versions]]
 version = "0.1.0"
 published = "2026-10-24"

mods/distant_horizons.toml

@@ -0,0 +1,33 @@
+id = "distant_horizons"
+kind = "native-mod"
+name = "Distant Horizons for Horizon Client"
+summary = "See far past your render distance: Distant Horizons' level-of-detail terrain, ported to Rust as a native mod."
+description = """
+An unofficial Rust port of [Distant Horizons](https://gitlab.com/distant-horizons-team/distant-horizons) by James Seibel and contributors: the world past your render distance, drawn at lower detail the farther it is.
+
+- Far terrain built from the chunks you visit, and in single player from the world generator, out to 64–1024 chunks.
+- Detail drops with distance by Distant Horizons' own rule, with its five quality presets.
+- LODs are kept on disk per world, so they load at once next time.
+- Drawn by Horizon's far-terrain renderer with block textures and biome tints.
+
+Settings: Options > Mods > Distant Horizons. In chat: `/dh` for status, `/dh distance 512`, `/dh quality high`, `/dh debug on` and more (Tab completes them).
+
+Native source mod: enable Settings → Game → Native mods (experimental), choose Build and confirm the native-code warning. The launcher downloads its own Rust and builds a separate game (10–30 minutes the first time). It runs with your account's permissions.
+
+Pinned to Horizon nightly `d009ebd140476b5bdc958c00f56a75e82abec691` (2026-10-29) and Horizon Mixins `0d6b103c70633d8fd9443d8d0acd3aadaacedb06`; the launcher builds these exact revisions. Other Horizon revisions have not been validated. It builds together with Horizon's official native mods; it can't be built with a native mod pinned to a different Horizon commit. Turn Video Settings > LOD Distance off: Horizon's own far terrain draws in the same place.
+
+Known limits: heavy at 256+ chunks (about 30–40 fps on an Apple M5 MacBook Pro); water at LOD edges can show see-through walls.
+
+LGPL-3.0, as Distant Horizons; its copyright notices are kept. Not made or endorsed by the Distant Horizons team. No Minecraft code or assets are included. Ported by Deniz Şahin with Claude (Anthropic)."""
+authors = ["denizsahin7744", "Deniz7744"]
+owners = ["denizsahin7744"]
+license = "LGPL-3.0-only"
+source = "https://github.com/denizsahin7744/distant-horizons-for-horizon-client"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-29"
+game = "26.3"
+file = "distant_horizons-0.1.0.hnmod"
+sha256 = "c53a2501f14efb624839329aac6999ddf8c64a399d41bec42a0c878902feea81"
+changelog = "First release: pinned to Horizon nightly d009ebd and Horizon Mixins 0d6b103."

mods/dynamic_lights.toml

@@ -0,0 +1,23 @@
+id = "dynamic_lights"
+kind = "native-mod"
+name = "Dynamic Lights"
+summary = "1:1 LambDynamicLights: handheld torches, lanterns, glowing items, dropped items, and glowing/burning entities illuminate their surroundings with water-sensitive"
+description = "A 1:1 native Rust port of LambDynamicLights for Horizon. Holding torches, lanterns, soul lanterns, glowstone, sea lanterns, shroomlights, lava buckets, blaze rods, glow ink sacs, or nether stars in your main hand or offhand smoothly illuminates the blocks and entities around you. Features authentic water-sensitive extinguishing (open-flame torches and campfires turn off underwater while lanterns, sea lanterns, glowstone, and shroomlights stay lit), dynamic lighting for dropped items and glowing/burning mobs (Blaze, Glow Squid, Magma Cube, Allay, Vex, swelling Creeper), and an L-key toggle."
+authors = ["CayMac"]
+owners = ["CayMac97"]
+license = "MIT"
+source = "https://github.com/CayMac97/dynamic-lights"
+key = "RWS411U2KXdTN4/y5bQhqBYxNlZvCtSZ5lNy46eeSAcgy0cxSJo2+Sm3"
+
+[[versions]]
+version = "1.0.0"
+published = "2026-10-31"
+game = "26.3"
+file = "dynamic_lights-1.0.0.hnmod"
+sha256 = "a2094d1bebafe5fce451debcf61345348a227bfe216f7d509284b5939f78fd7b"
+signature = """
+untrusted comment: signature from minisign secret key\r
+RUS411U2KXdTN/4L0gk0/eCHlpDto1P6pB5IGmrdpiN6dSVHl9abM/WLLBRDEtuThgX4lXj6nwfCBiRP3m90Sxvb6CdtlXelmwM=\r
+trusted comment: timestamp:1793444194\tfile:dynamic_lights-1.0.0.hnmod\thashed\r
+L+7ZlDA6FCwA8arKDsf3Yj3lmupO4tGI33oVroRQFGm1hqQNt6xZDIE1lLwtisD54ZJK03Tu41pImSbDcO+CCQ=="""
+changelog = "Initial Release for 26.3 Horizon. "

mods/eatinganimation.toml

@@ -0,0 +1,46 @@
+id = "eatinganimation"
+kind = "native-mod"
+name = "Eating Animation"
+summary = "While you eat food, or drink a potion or milk, the item in your hand shows its bitten frames."
+description = """
+It is a port of [Eating Animation](https://github.com/Theoness1/EatingAnimation) for Horizon.
+
+While you eat food, or drink a potion or milk, the item in your hand shows its bitten frames.
+
+The frames come from a resource pack you build from your own copy of the EatingAnimation download with `tools/make_frame_pack.py`, and drop into Horizon's `resourcepacks/` folder.
+
+~~Or you can just download it from GitHub Releases...~~"""
+authors = ["soufi"]
+owners = ["soufied"]
+license = "MIT"
+source = "https://github.com/soufied/EatingAnimation-Horizon"
+icon = "icons/eatinganimation.png"
+key = "RWT6eNq4e5WfVDA2lzOOi6XCm/+jJgilqT1+HUUM33ie5MCjcRfSg760"
+
+[[versions]]
+version = "0.1.1"
+published = "2026-10-31"
+game = "26.3"
+file = "eatinganimation-0.1.1.hnmod"
+sha256 = "3b4d7ce3c9791facc862da7727c2c7c71025cd9bb3ee4cbeaf40f48c72bf5cb0"
+signature = """
+untrusted comment: signature from minisign secret key
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+trusted comment: timestamp:1793419092\tfile:eatinganimation-0.1.1.hnmod\thashed
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+changelog = """
+dumped to v0.1.1
+added icon"""
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "eatinganimation-0.1.0.hnmod"
+sha256 = "07ef4fde3ebbc4f132aab593b12187bce15e1a46689ab40bd3067c685aca85b9"
+signature = """
+untrusted comment: signature from minisign secret key
+RUT6eNq4e5WfVJPSxJOh730W1FMzydyVRO2S58rux9xbEtEU+mDgsqWX65rscWaUH3zqOkLan6quW/u9nEZDgXrNz1n6IHnT5Aw=
+trusted comment: timestamp:1793371727\tfile:eatinganimation-0.1.0.hnmod\thashed
+qCCGAWAc39kDujbX9CsdXu/URjpNybAOxkomTi18GnzJhMLtsbj0ZfVJaVCSxnh0VvznGQvoH9/DEdRAxBAVBg=="""
+changelog = "First release. Eating Animation for Horizon as a native mod: the food, milk and potion in your hand show bitten frames while you eat or drink them."

mods/enchantmenthints.toml

@@ -15,7 +15,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/enchantmenthints"
-icon = "https://raw.githubusercontent.com/d3grando/enchantmenthints/main/icon.png"
+icon = "icons/enchantmenthints.png"
 
 [[versions]]
 version = "0.1.0"

mods/fly_speed.toml

@@ -0,0 +1,23 @@
+id = "fly_speed"
+kind = "native-mod"
+name = "Fly Speed"
+summary = "Allows you to change your fly speed"
+description = "Fly 0.1x to 20x your normal speed: /flyspeed, /flyspeed +1 to step, /flyspeed reset for 1x. Native Horizon mod."
+authors = ["ImmortalDev"]
+owners = ["ImmortalWhisper"]
+license = "All Rights Reserved"
+source = "https://github.com/ImmortalWhisper/Fly-Speed"
+key = "RWSy3RAfbzD2a0WMm0tQlVl+3GHigjwvwXKvzvnwfmoYrIAoIffbrSbP"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "fly_speed-0.1.0.hnmod"
+sha256 = "c50a3dcfd9ff68af00560f9cd330c4d18b3d9028113b6769ded54997d5267ddf"
+signature = """
+untrusted comment: signature from minisign secret key\r
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+trusted comment: fly_speed-0.1.0.hnmod\r
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+changelog = "Created Mod"

mods/fullbright.toml

@@ -0,0 +1,29 @@
+id = "fullbright"
+kind = "native-mod"
+name = "MoreGamma"
+summary = "Brightness past 100%: set your own gamma with /gamma, or toggle full brightness with /fullbright."
+description = """
+A native Horizon mod: the launcher builds it into the game (Settings → Game → Native mods, then Build). Native mods are not sandboxed and run with your account's rights, so read the source before you build it. Uses only Horizon's native hook points (hooks 1); tested on Horizon 41672b1 and horizon-mixins 0d6b103.
+
+See in the dark without torches or night vision. MoreGamma lets you set the brightness (gamma) far past the video settings' 100% "Bright" limit, with a chat command, and switch full brightness on and off.
+
+- `/gamma <value>`: your own gamma. `1` is vanilla's "Bright", `15` is fullbright, up to `100`; `/gamma 1500%` works too.
+- `/gamma` shows the gamma in effect.
+- `/gamma reset` (or `off`) goes back to your video settings slider; `/gamma on` turns your last custom gamma on again.
+- `/fullbright` toggles full brightness (gamma 15).
+- Options → Mods → Fullbright: an on/off button, a button cycling 100/200/500/1000/1500%, and a toggle key you can bind.
+
+Client-side: the commands are handled by your game before anything reaches a server, so it works in single player, on LAN and on servers. Your brightness slider and `options.txt` are never changed, so turning it off gives your own brightness back. Settings are remembered between sessions."""
+authors = ["bezi5kt"]
+owners = ["bezi5kt"]
+license = "MIT"
+source = "https://github.com/bezi5kt/gamma-rust"
+icon = "icons/fullbright.png"
+
+[[versions]]
+version = "1.0.0"
+published = "2026-10-30"
+game = "26.3"
+file = "fullbright-1.0.0.hnmod"
+sha256 = "573c5e04188e0b1a26eb42a8aeaeeefeb6fb334a096afaa834e71b8efa353ad7"
+changelog = "First release."

mods/itemnew.toml

@@ -15,7 +15,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/itemnew"
-icon = "https://raw.githubusercontent.com/d3grando/itemnew/main/icon.png"
+icon = "icons/itemnew.png"
 
 [[versions]]
 version = "0.1.1"

mods/jei.toml

@@ -0,0 +1,96 @@
+id = "jei"
+kind = "native-mod"
+name = "JEI for Horizon"
+summary = "An item and recipe viewer for Horizon: every item beside container screens, with search, recipes and uses"
+description = """
+An item and recipe viewer for [Horizon](https://playhorizon.dev), the Rust reimplementation of Minecraft: Java Edition.
+
+Horizon JEI is inspired by [JustEnoughItems (JEI)](https://github.com/mezz/JustEnoughItems). JEI serves as the reference specification, while this project is a completely new Rust implementation built around Horizon's native hook points.
+
+**Version 0.1.0 — Core Viewer**
+
+### Features
+
+- **Item Browser:** Browse every item registered by the game through a paginated panel alongside container screens, with a search bar supporting JEI's search grammar: words, `"quoted phrases"`, `-exclusions`, `|` alternatives, `@namespace`, and `#tag`.
+- **Recipe Viewer:** Press **R** to view an item's recipes or **U** to see its uses. Both work over the item panel and container slots.
+- **Recipe Categories:** Dedicated tabs for crafting, furnace, blast furnace, smoker, campfire, stonecutter, smithing, and brewing, supporting all five of the game's recipe layouts, including cooking time and XP.
+- **Recipe Navigation:** Browse recipe history with **Back** and click recipe slots to open the corresponding item.
+- **Recipe Placement:** Use the **+** button to place a recipe into the open crafting grid, provided it is available in the recipe book.
+- **Item Giving:** Give items through Options → Mods → JEI or `/jei give`. In creative mode, left-click gives one item and right-click gives a full stack. In survival mode, clicking opens the recipe viewer instead.
+- **Localization:** English and Spanish interface translations. Item names are retrieved directly from the game and respect the player's language.
+- **Diagnostics:** `/jei` reports the game's recipe table sizes.
+
+### Current Limitations
+
+The 0.1.0 release focuses on the core viewer. Bookmarks, container slot click integration, tooltips, creative inventory integration, non-recipe categories (anvil, grindstone, composter, and fuel), and shift-click recipe placement are not yet supported.
+
+Some of these features require native hook points that Horizon does not currently expose. See the [JEI parity matrix](https://github.com/enderliker/horizon-jei/blob/main/docs/jei-parity.md) for implementation details.
+
+### Requirements & Security
+
+Requires Horizon **26.3**, hook points version **2**, and the current Nightly build.
+
+Horizon native mods are compiled directly into the game and are **not sandboxed**. Only build source code you trust.
+
+Horizon JEI reads the game's tables, container interface, chat, and its own settings directory (`horizon-mods/.horizon-mod-data/jei/`). It does not write to any other location.
+
+*Unofficial project. Not affiliated with mezz, Mojang, Microsoft, or the Horizon project.*"""
+authors = ["enderliker"]
+owners = ["enderliker"]
+license = "MIT"
+source = "https://github.com/enderliker/horizon-jei"
+key = "RWRqzx718YYz/OHRM+pAnFWlDv8Rrgar5C4NszQg3EKJWQZWNel5Sslf"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "jei-0.1.0.hnmod"
+sha256 = "c5590e0d4618d435fc0c56abcc9cdabf253be694710068a3dd4643ac25466b5b"
+signature = """
+untrusted comment: signature from minisign secret key
+RURqzx718YYz/AZEFNcRh0lQFAgg8JsladNTOULcWqBnZFoFoApH0UvoQQkTk8wC/LfZpfJkrn7XRzSUOPUOfudUebBSHHdVYQ0=
+trusted comment: jei 0.1.0 for Horizon 26.3
+OqC3JuFFGuGNdxATsGIvM20nrld1ME2ks3tI2hfaMX2s5bCgwYjieUDk7FbDQD8zxd3KHqOYaUTz6T+njgUNCw=="""
+changelog = """
+The first playable Horizon JEI viewer, built on Horizon's native hook points (version 2).
+
+### Item Browser & Search
+- Added an item panel alongside container screens, displaying every item known to the game with pagination.
+- Implemented JEI's search grammar:
+  - Words and `"quoted phrases"`.
+  - `-exclusions` and `|` alternatives.
+  - `@namespace` and `#tag` filters.
+  - `$tooltip` and `%creative tab` are not supported yet, pending access to the required data.
+
+### Recipe & Usage Viewer
+- Press **R** to view an item's recipes and **U** to view its uses.
+- Works over the item panel and any slot in a container screen.
+- Clicking an item in the panel opens the same views.
+- Added recipe pages with dedicated tabs for:
+  - Crafting
+  - Furnace
+  - Blast Furnace
+  - Smoker
+  - Campfire
+  - Stonecutter
+  - Smithing
+  - Brewing
+- Supports all five of the game's recipe layouts, including cooking time and XP.
+- Added a **Back** button to navigate through viewing history.
+- Clicking a recipe slot opens that item's recipes.
+
+### Recipe Placement
+- Added the **+** button to place recipes into the open crafting grid when the recipe book contains them.
+- The button remains disabled until the recipe is available in the recipe book.
+- Shift-click is not supported yet because the panel's action event does not expose modifier keys.
+
+### Item Giving
+- Added item giving through **Options → Mods → JEI** or `/jei give`.
+- In creative mode, left-click gives one item and right-click gives a full stack.
+- In survival mode, clicking an item opens its recipes instead.
+
+### Localization & Diagnostics
+- Added English and Spanish UI translations, configurable through the mod's **Language** setting.
+- Item names are retrieved directly from the game and always respect the player's language.
+- Added `/jei` to report the game's table sizes."""

mods/lookat.toml

@@ -1,26 +1,30 @@
 id = "lookat"
-kind = "mod"
+kind = "native-mod"
 name = "LookAt"
-summary = "The block under your crosshair as a vanilla tooltip: its icon, its name in your language and where it comes from. Reach up to 1024 blocks"
+summary = "The block or mob under your crosshair as a vanilla tooltip: icon, name in your language, health, the tool it needs and where it comes from"
 description = """
-The block under your crosshair at the top of the screen, drawn as a vanilla tooltip: its item's icon, its name in your language and the namespace it comes from.
+The block or entity under your crosshair at the top of the screen, drawn as a vanilla tooltip: its item's icon, its name in your language and the namespace it comes from.
 
-**Settings** (Options → Mods → LookAt):
+- **Blocks**: up to 1024 blocks away, across distant terrain.
+- **Mobs and players**: name and health as hearts or numbers; boats, minecarts, armor stands, paintings and item frames (with what they hold).
+- **Harvest tool**: ✔ or ✘ with the tool a block needs.
 
-- **Range**: Reach (5 blocks), 16, 64 or 1024 blocks, across distant terrain
-- **Position**: Top, Top left, Top right
-- **Background opacity**: 100%, 75%, 50%, 25%
-- **Item icon**, **Where it comes from**: on or off
-- **Position and distance**: the block's coordinates and how far it is
+**Settings** (Options → Mods → LookAt): range, position (top, top left, top right), size, background opacity, item icon, where it comes from, position and distance, entities, health, harvest tool. Boxes keep clear of F3, boss bars, the minimap and effect icons.
 
-To make the box bigger, raise the game's GUI Scale.
-
-**Blocks only for now**: the mod API can't see entities yet, so mobs show nothing."""
+**Now a native mod (0.2.1)**: the launcher builds it into the game (Settings → Game → Native mods (experimental), then Build). Native mods are not sandboxed and run with your account's permissions, so read the source before you build it. Tested against Horizon `142388e1c136e622652ec7505af15d8ad195e041` with Horizon Mixins `0d6b103c70633d8fd9443d8d0acd3aadaacedb06`; the launcher builds these exact pinned revisions. Settings from 0.1.0 carry over. 0.1.0 is the WebAssembly version."""
 authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/lookat"
-icon = "https://raw.githubusercontent.com/d3grando/lookat/main/icon.png"
+icon = "icons/lookat.png"
+
+[[versions]]
+version = "0.2.1"
+published = "2026-10-29"
+game = "26.3"
+file = "lookat-0.2.1.hnmod"
+sha256 = "6c15726116825b5955984223d0e1bccd5d18375005af243a061b2ba2b9139f33"
+changelog = "Now a native mod (WebAssembly code mods are going away). New: mobs, players and other entities under the crosshair with their health, the harvest tool a block needs, a size setting, and boxes that keep clear of F3, boss bars, the minimap and effect icons. Pinned to Horizon 142388e and Horizon Mixins 0d6b103."
 
 [[versions]]
 version = "0.1.0"

mods/mousetricks.toml

@@ -15,7 +15,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/mousetricks"
-icon = "https://raw.githubusercontent.com/d3grando/mousetricks/main/icon.png"
+icon = "icons/mousetricks.png"
 
 [[versions]]
 version = "0.2.0"

mods/recipes.toml

@@ -1,5 +1,5 @@
 id = "recipes"
-kind = "mod"
+kind = "native-mod"
 name = "Recipes"
 summary = "Every item beside your inventory, with its recipes and uses."
 description = """
@@ -13,11 +13,25 @@ Horizon's own recipe viewer.
 - On servers that are not Horizon, it shows this game's own 26.3 recipes. Which recipes you know, and what + can fill, follow the server's recipe book.
 
 It reads the game's items and recipes, hears its own keys and your clicks on the panel, and places recipes or gives items only when you ask: nothing else.
+
+Now a native mod (2.0.0): built into the game by the launcher, on the Horizon you play, like any native mod
+(Settings → Game → Native mods (experimental), then Build). It needs Horizon's native hook points version 2, in the
+Nightlies from 4baa571 on. Your settings and keys carry over from 1.0.0. Turn it off in Options > Mods: it rests at
+once, and the next build leaves it out. Its source is
+[horizon-mods/native/recipes](https://github.com/horizon-rust/horizon-mods/tree/main/native/recipes).
 """
 authors = ["Horizon"]
 owners = ["ludovic111"]
 license = "MIT"
-source = "https://github.com/horizon-rust/horizon/tree/main/mods/official/recipes"
+source = "https://github.com/horizon-rust/horizon-mods/tree/main/native/recipes"
+
+[[versions]]
+version = "2.0.0"
+published = "2026-10-29"
+game = "26.3"
+file = "recipes-2.0.0.hnmod"
+sha256 = "51fddf300709404170061355afdf0b407f28eb928bcc0a9133c241cd63f4a0ed"
+changelog = "Native: built into the game by the launcher on Horizon's native hook points (version 2); settings and keys carry over; turn it off in Options > Mods."
 
 [[versions]]
 version = "1.0.0"

mods/rightharvest.toml

@@ -0,0 +1,21 @@
+id = "rightharvest"
+kind = "native-mod"
+name = "RightClickHarvest"
+summary = "Right-click a ripe crop to pick it and sow it again."
+description = """
+With an empty hand, right-click a ripe wheat, carrot, potato, beetroot or nether wart: the crop is harvested with the game's own drops, sound and statistics, and sown again from a seed in your inventory.
+
+No settings: turn it off in Options > Mods."""
+authors = ["Domanffe"]
+owners = ["Domanffe"]
+license = "MIT"
+source = "https://github.com/Domanffe/rightharvest"
+icon = "https://horizon-rust.github.io/horizon-mods/icons/rightharvest.png"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "rightharvest-0.1.0.hnmod"
+sha256 = "a43870a89827c1d0fa861a663aa1781819b236f994191abf971c98125a3a4653"
+changelog = "First release: a native mod for Horizon 26.3. With an empty hand, right-click a ripe crop to harvest it with the game's own drops and sow it again from a seed you carry."

mods/serverify.toml

@@ -0,0 +1,56 @@
+id = "serverify"
+kind = "native-mod"
+name = "Serverify"
+summary = "Find Minecraft servers and add them to your Multiplayer list, from a page in your web browser."
+description = """
+Serverify is a server browser. Press **F8** (or type `/serverify web`, or press the button on the mod's settings page) and your web browser opens a page with a search box, a category menu and cards showing each server's picture, address, player count and country. Press **Add** and the server goes to the top of your Multiplayer list. Then join it from Horizon's own Multiplayer screen.
+
+It is the Horizon version of [Serverify](https://github.com/Louchatfroff/serverify), the server browser for Fabric, Quilt, Forge and NeoForge, by the same author.
+
+## What it does
+
+- Opens a server browser page in your web browser: search, 22 categories, an offline-mode filter and an **Add** button.
+- Adds servers to `servers.dat` in the game folder, with the name cleaned of colour codes.
+- Adds chat commands: `/serverify web`, `list [category]`, `search <words>`, `next`, `prev`, `add <number>` and `categories`.
+- Adds a row in Options > Mods with a rebindable key (F8 by default) and a settings page with two buttons: open the browser, and **Offline-mode servers only** (on by default).
+
+Horizon cannot join servers that check Minecraft accounts yet, which is most public servers, so by default the page shows servers that accept offline-mode players. Turn the filter off to see all of them.
+
+## What it contacts
+
+- **Modrinth.** The game asks `api.modrinth.com` for the server list and `cdn.modrinth.com` for server pictures, only when you look for servers.
+- **Three listing sites.** With the offline-mode filter off (and for top-mc-servers.net's list of cracked servers when it is on), the game fetches public pages of `top-mc-servers.net`, `minecraftservers.org` and `minecraft-mp.com`, and their server pictures. The game builds those addresses itself. The page reads the fetched pages with the browser's own HTML parser.
+- **A page on your computer.** The first time you open the page, the mod starts a small web server on `127.0.0.1` (this computer only, never the network) with a random secret in its address, made for each session. The page talks only to that server. A request with another host name, another origin or no secret is refused. The server can show the list, send a picture and add one server to your Multiplayer list.
+- It sends no data about you, and makes no request at any other time.
+
+## What it does not do
+
+- It does not run any code from the sites it reads, and it does not send your data anywhere.
+- It does not change anything but `servers.dat` (one entry at a time) and its own settings in `horizon-mods/.horizon-mod-data/serverify/`.
+- It does not draw screens or buttons in the game: Horizon's hook points have none, so the screen is your web browser.
+- It cannot make Horizon join servers that check Minecraft accounts.
+- Adding a server rewrites `servers.dat`, which drops the hidden direct-join entries Horizon keeps. Your saved servers stay.
+
+## Install
+
+Install it from the launcher's Mods page, then Settings > Native mods (experimental) > Build, and play the Native mods instance. Guide: https://github.com/Louchatfroff/serverify/tree/main/horizon/serverify#readme
+
+Native mods are not sandboxed. The source is public and licensed GPL-3.0-only: https://github.com/Louchatfroff/serverify/tree/main/horizon/serverify"""
+authors = ["Louchatfroff"]
+owners = ["Louchatfroff"]
+license = "GPL-3.0-only"
+source = "https://github.com/Louchatfroff/serverify"
+icon = "icons/serverify.png"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-30"
+game = "26.3"
+file = "serverify-0.1.0.hnmod"
+sha256 = "f9ad0777f8fc7ea532f799da8a9eb72df2348c8d6bb5dc104f81b6ab47209501"
+changelog = """
+First release for Horizon, ported from the Java Edition mod of the same name.
+
+- A server browser page in your web browser (F8, `/serverify web`, or the settings button).
+- Chat commands to list, search and add servers.
+- An offline-mode filter, on by default, because Horizon cannot join servers that check Minecraft accounts yet."""

mods/shulker_peek.toml

@@ -0,0 +1,31 @@
+id = "shulker_peek"
+kind = "native-mod"
+name = "ShulkerPeek"
+summary = "A shulker box's contents as a 9 x 3 grid in its tooltip."
+description = """
+Hover a shulker box to see what's inside: its 27 slots appear as a 9 x 3 grid right in the tooltip, laid out exactly like the box's own screen, with item icons and stack counts.
+
+- Works with the plain shulker box and all 16 dyed ones, whether empty, partly filled or full.
+- Works on every screen with item tooltips: your inventory, chests and other containers, the creative inventory, the item panel, chat item links and trading.
+- Keeps the tooltip's usual lines (name, lore, "64 x Diamond"...); the grid goes underneath.
+- Respects hidden tooltips: a box whose `minecraft:tooltip_display` hides its contents stays hidden.
+- Settings in Options > Mods > ShulkerPeek > Settings: show the grid always or only while holding Shift, show a grid for empty boxes, and tint the grid with the box's dye colour.
+- Uses your resource pack's own shulker box texture.
+
+Works in single player and on LAN worlds you host. Horizon currently leaves a box's contents out of what its built-in server sends to the game window, which is why even the "64 x Diamond" lines are missing there. ShulkerPeek sends the contents the way a vanilla server does. On vanilla servers the grid works too; on other Horizon servers without the mod, boxes look empty.
+
+It never changes items, inventories or worlds. Turn it off any time in Options > Mods.
+
+This is a native mod built for Horizon Nightly 2026-10-29 (`5e391eb`). It builds together with Horizon's official native mods (FPS Counter, Zoom, Minimap, Recipes and others)."""
+authors = ["vstxx"]
+owners = ["vstxx"]
+license = "MIT"
+source = "https://github.com/vstxx/shulkerpeek"
+icon = "icons/shulker_peek.png"
+
+[[versions]]
+version = "0.1.0"
+published = "2026-10-29"
+game = "26.3"
+file = "shulker_peek-0.1.0.hnmod"
+sha256 = "e4e33cb698d91042b2ed2f93a1c935f279d16d83988115d53c0f33530cabeab5"

mods/smartf3.toml

@@ -16,7 +16,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/smartf3"
-icon = "https://raw.githubusercontent.com/d3grando/smartf3/main/icon.png"
+icon = "icons/smartf3.png"
 
 [[versions]]
 version = "0.1.0"

mods/treefall.toml

@@ -16,7 +16,7 @@ authors = ["d3grando"]
 owners = ["d3grando"]
 license = "MIT"
 source = "https://github.com/d3grando/treefall"
-icon = "https://raw.githubusercontent.com/d3grando/treefall/main/icon.png"
+icon = "icons/treefall.png"
 
 [[versions]]
 version = "0.3.0"

mods/xtoxray.toml

@@ -0,0 +1,33 @@
+id = "xtoxray"
+kind = "native-mod"
+name = "X To Xray"
+summary = "Opensource Xraymod"
+description = """
+Press X To Xray!
+Does Not Work On Servers.
+
+Instalation:
+1. Download Horizon
+2. Get Horizon Working
+3. Add The Mod Trough The Horizon Launcher
+4. Start Xraying
+"""
+authors = ["1_st_Cat"]
+owners = ["RealCat1st"]
+license = "Apache-2.0"
+source = "https://github.com/RealCat1st/XToXrayRust"
+icon = "icons/xtoxray.png"
+key = "RWQVF+EFGGnX6eUNms+cP5AceLvx9b0rFYYXCty7so4MVbJ1SNpi9zNK"
+
+[[versions]]
+version = "2026.29.0"
+published = "2026-10-30"
+game = "26.3"
+file = "xtoxray-2026.29.0.hnmod"
+sha256 = "3446a4a70a2b87ef6e9de00ce8a255aa83c2e44ccd5acc9f14887662ed55f27c"
+signature = """
+untrusted comment: signature from rsign secret key
+RUQVF+EFGGnX6cZkn/iGZ9FUHXC45MU+8uuj7l7eRkZ+bR/x7S8s2U34F7nv/f6jKXdzeLZi3QoSA5g5oXqP99/KlGgd/19ygwY=
+trusted comment: timestamp:1793375231\tfile:xtoxray-2026.29.0.hnmod\tprehashed
+2h6QOc/dnek1KMCGL2jerhCObc9pECmShr0kKYJhEEFz52Hhb4C3vmjc9vuwE3CftUHs+StHkalHQVLVQy8eCg=="""
+changelog = "Release"

native/coords-hud/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "horizon-mod-coords-hud"
+version = "2.0.0"

native/coords-hud/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "horizon-mod-coords-hud"
+version = "2.0.0"
+edition = "2024"
+license = "MIT"
+publish = false
+description = "Horizon's Coordinates HUD, a native mod: your position and facing in a corner of the screen."
+
+# The mod's logic and its tests: the same file the bundle adds to the game.
+[lib]
+path = "mixins/coords_hud/runtime.rs"

native/coords-hud/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Ludovic Marie and the Horizon contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

native/coords-hud/README.md

@@ -0,0 +1,46 @@
+# Coordinates HUD (Horizon native mod)
+
+Your block position and the direction you face in a box in the top-left corner of the screen.
+
+- `/where` puts your coordinates and dimension in chat.
+- `/coords` hides or shows the box, and the game keeps your choice (also Options > Mods > Coordinates HUD > Settings).
+
+It is a [horizon-mixins](https://github.com/horizon-rust/horizon-mixins) bundle (`mixins/coords_hud/`) that the Horizon
+launcher builds into the game. It replaces the WebAssembly Coordinates HUD 0.1.0, the WebAssembly SDK's example mod.
+The time of day line is gone: Horizon's hook points don't give the game's clock yet.
+
+## Install
+
+In the Horizon launcher: Mods → Coordinates HUD → Install, then Settings → Game → Native mods (experimental) → Build. The
+launcher downloads its own Rust and builds the game with your native mods; see Horizon's
+[native mods](https://github.com/horizon-rust/horizon/blob/main/docs/native-mods.md).
+
+## Made on the hook points
+
+The bundle hooks only Horizon's native hook points (`crates/horizon-client/src/game/native_hooks.rs`), which keep
+their names and signatures across releases. `compatibility.json` names the version it needs (`"hooks": 1`), so the
+launcher builds it on any Horizon with that version or a later one, together with any other mod. `horizon_revision` is
+only the commit it was last tested on.
+
+| File | What it is |
+|---|---|
+| `mixins/coords_hud/horizon-mixin.toml` | The bundle: one module and the HEAD hooks |
+| `mixins/coords_hud/runtime.rs` | The mod's logic and state, added to the game as `game::official_coords_hud`; also this crate's library, for its tests |
+| `mixins/coords_hud/*.rs` | One small helper per hook |
+| `proof.py` (with `../tools/game.py`) | The proof: the built game driven with `horizon-ctl --offscreen` on fresh, temporary data |
+
+## Build and prove
+
+```sh
+(cd native/coords-hud && cargo test)                     # the logic
+python3 native/tools/native.py check coords-hud          # apply on the tested Horizon and cargo check the game
+python3 native/tools/native.py check all                 # with the other native mods, as a player's set
+python3 native/tools/native.py package coords-hud        # native/target/coords_hud-<version>.hnmod for the registry
+python3 native/tools/native.py proof coords-hud --resources /path/to/.local/horizon-client/26.3
+```
+
+The proof needs resources prepared from your own Minecraft 26.3 (`horizon-prepare`); none are in this repository.
+It checks the row and the settings page in Options > Mods, that the box shows in the top left, that `/coords` hides it
+and writes `horizon-mods/.horizon-mod-data/coords_hud/shown`, and takes a screenshot of `/where`'s line in chat.
+
+License: MIT.

native/coords-hud/compatibility.json

@@ -0,0 +1,8 @@
+{
+  "game": "26.3",
+  "hooks": 1,
+  "horizon_repository": "https://github.com/horizon-rust/horizon",
+  "horizon_revision": "4baa571566e39bfd6594988d3bb2bc85440c30e7",
+  "horizon_mixins_repository": "https://github.com/horizon-rust/horizon-mixins",
+  "horizon_mixins_revision": "0d6b103c70633d8fd9443d8d0acd3aadaacedb06"
+}

native/coords-hud/mixins/coords_hud/click.rs

@@ -0,0 +1,10 @@
+// A click on the mod's settings page: show or hide the box, and keep it.
+fn official_coords_hud_click(game: &mut crate::game::Game<'_>, mod_id: &str, button: usize) {
+    use crate::game::official_coords_hud as m;
+    if mod_id != m::ID || button != 0 {
+        return;
+    }
+    let shown = !m::shown(|| game.native_setting(m::ID, "shown"));
+    m::set_shown(shown);
+    game.native_set_setting(m::ID, "shown", if shown { "true" } else { "false" });
+}

native/coords-hud/mixins/coords_hud/command.rs

@@ -0,0 +1,20 @@
+// /where puts the position in chat; /coords hides or shows the box.
+fn coords_hud_command(game: &mut crate::game::Game<'_>, command: &str, ran: &mut bool) {
+    use crate::game::official_coords_hud as m;
+    let name = command.split(' ').next().unwrap_or("");
+    if !game.native_on(m::ID) || !matches!(name, "where" | "coords") {
+        return;
+    }
+    *ran = true;
+    if name == "coords" {
+        let shown = !m::shown(|| game.native_setting(m::ID, "shown"));
+        m::set_shown(shown);
+        game.native_set_setting(m::ID, "shown", if shown { "true" } else { "false" });
+        game.native_chat(if shown { "Coordinates panel shown" } else { "Coordinates panel hidden" });
+        return;
+    }
+    match game.native_player() {
+        Some(p) => game.native_chat(&m::where_line(p.x, p.y, p.z, p.dimension)),
+        None => game.native_chat("Not in a world"),
+    }
+}

native/coords-hud/mixins/coords_hud/horizon-mixin.toml

@@ -0,0 +1,68 @@
+[mod]
+id = "coords_hud"
+version = "2.0.0"
+priority = 100
+
+# The commit it was tested on. It uses only the native hook points (hooks 1 in
+# compatibility.json): the launcher builds it on any Horizon that has them.
+[compatibility]
+horizon_revision = "4baa571566e39bfd6594988d3bb2bc85440c30e7"
+
+[[module]]
+id = "runtime"
+file = "crates/horizon-client/src/game.rs"
+name = "official_coords_hud"
+source = "runtime.rs"
+
+[[injection]]
+id = "hud"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_hud"
+helper = "hud.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "batch", ty = "&mut horizon_client::hud::HudBatch", value = "&mut *batch" },
+  { name = "corners", ty = "&mut horizon_client::extras_hud::Corners", value = "&mut *corners" },
+]
+
+[[injection]]
+id = "command"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_command"
+helper = "command.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "command", ty = "&str", value = "command" },
+  { name = "ran", ty = "&mut bool", value = "&mut *ran" },
+]
+
+[[injection]]
+id = "list"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_mods"
+helper = "list.rs"
+bindings = [
+  { name = "mods", ty = "&mut Vec<crate::game::native_hooks::NativeMod>", value = "&mut *mods" },
+]
+
+[[injection]]
+id = "settings"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_settings"
+helper = "settings.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "mod_id", ty = "&str", value = "mod_id" },
+  { name = "buttons", ty = "&mut Vec<String>", value = "&mut *buttons" },
+]
+
+[[injection]]
+id = "click"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_settings_click"
+helper = "click.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "mod_id", ty = "&str", value = "mod_id" },
+  { name = "button", ty = "usize", value = "button" },
+]

native/coords-hud/mixins/coords_hud/hud.rs

@@ -0,0 +1,28 @@
+// The box in the top-left corner, drawn as the WebAssembly mods' panels were;
+// the debug screen takes that corner.
+fn coords_hud(
+    game: &mut crate::game::Game<'_>,
+    batch: &mut horizon_client::hud::HudBatch,
+    corners: &mut horizon_client::extras_hud::Corners,
+) {
+    use crate::game::official_coords_hud as m;
+    use horizon_client::extras::Corner;
+    // Turned off in Options > Mods: nothing until the next build leaves it out.
+    if !game.native_on(m::ID) || !game.native_corner_shown(Corner::TopLeft) {
+        return;
+    }
+    if !m::shown(|| game.native_setting(m::ID, "shown")) {
+        return;
+    }
+    let Some(p) = game.native_player() else {
+        return;
+    };
+    let lines = m::lines(p.x, p.y, p.z, p.yaw);
+    let w = lines.iter().map(|l| game.native_text_width(l)).fold(0.0, f32::max) + 4.0;
+    let h = 10.0 * lines.len() as f32 + 2.0;
+    let (x, y) = corners.place(Corner::TopLeft, w, h);
+    game.native_fill(batch, [x, y, w, h], m::BACKGROUND);
+    for (i, line) in lines.iter().enumerate() {
+        game.native_text(batch, line, [x + 2.0, y + 2.0 + 10.0 * i as f32], m::INK, true);
+    }
+}

native/coords-hud/mixins/coords_hud/list.rs

@@ -0,0 +1,10 @@
+// The mod's row in Options > Mods.
+fn official_coords_hud_listed(mods: &mut Vec<crate::game::native_hooks::NativeMod>) {
+    use crate::game::official_coords_hud as m;
+    mods.push(crate::game::native_hooks::NativeMod {
+        id: m::ID.into(),
+        title: format!("{} {}", m::NAME, m::VERSION),
+        description: m::DESCRIPTION.into(),
+        keys: Vec::new(),
+    });
+}

native/coords-hud/mixins/coords_hud/runtime.rs

@@ -0,0 +1,100 @@
+// Horizon's Coordinates HUD, formerly the WebAssembly SDK's example mod: the
+// block position and the direction the player faces in a box in the top-left
+// corner, `/where` to put the position in chat and `/coords` to hide or show
+// the box. This file is both the mod's Cargo library (its tests) and the
+// module the bundle adds to the game.
+
+/// The mod's id (its settings folder), name and version.
+pub const ID: &str = "coords_hud";
+pub const NAME: &str = "Coordinates HUD";
+pub const VERSION: &str = "2.0.0";
+pub const DESCRIPTION: &str = "Your coordinates and facing in a corner of the screen. /where puts them in chat, /coords hides or shows the box.";
+/// The WebAssembly mods' panel: translucent black, white text with a shadow.
+pub const BACKGROUND: u32 = 0x7800_0000;
+pub const INK: u32 = 0xFF_FFFF;
+
+/// Direction.fromYRot: yaw 0 faces south, 90 west.
+pub fn facing(yaw: f32) -> &'static str {
+    let i = (yaw / 90.0 + 0.5).floor() as i32 & 3;
+    ["South (+Z)", "West (-X)", "North (-Z)", "East (+X)"][i as usize]
+}
+
+/// The box's lines, as the WebAssembly mod wrote them.
+pub fn lines(x: f64, y: f64, z: f64, yaw: f32) -> [String; 2] {
+    [
+        format!("XYZ {x:.1} / {y:.1} / {z:.1}"),
+        format!("Facing {}", facing(yaw)),
+    ]
+}
+
+/// `/where`'s line: `12, 70, -4 in minecraft:the_nether`.
+pub fn where_line(x: f64, y: f64, z: f64, dimension: &str) -> String {
+    format!(
+        "{:.0}, {:.0}, {:.0} in {dimension}",
+        x.floor(),
+        y.floor(),
+        z.floor()
+    )
+}
+
+/// The stored `shown` value: shown unless it says `false`.
+pub fn read_shown(stored: Option<String>) -> bool {
+    stored.is_none_or(|v| v.trim() != "false")
+}
+
+pub fn shown_label(shown: bool) -> String {
+    format!("Shown: {}", if shown { "ON" } else { "OFF" })
+}
+
+thread_local! {
+    /// Whether the box shows, read once from its file, then kept.
+    static SHOWN: std::cell::Cell<Option<bool>> = const { std::cell::Cell::new(None) };
+}
+
+/// Whether the box shows, read once through `get` (the `shown` file).
+pub fn shown(get: impl FnOnce() -> Option<String>) -> bool {
+    SHOWN.with(|s| {
+        let found = s.get().unwrap_or_else(|| read_shown(get()));
+        s.set(Some(found));
+        found
+    })
+}
+
+/// Replaces it (`/coords` or the settings page changed it).
+pub fn set_shown(shown: bool) {
+    SHOWN.with(|s| s.set(Some(shown)));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn facing_follows_vanilla_yaw() {
+        assert_eq!(facing(0.0), "South (+Z)");
+        assert_eq!(facing(90.0), "West (-X)");
+        assert_eq!(facing(-180.0), "North (-Z)");
+        assert_eq!(facing(-90.0), "East (+X)");
+        assert_eq!(facing(314.0), "East (+X)");
+    }
+
+    #[test]
+    fn lines_read_as_the_webassembly_mods() {
+        assert_eq!(
+            lines(12.5, 64.0, -3.25, 180.0),
+            ["XYZ 12.5 / 64.0 / -3.2", "Facing North (-Z)"]
+        );
+        assert_eq!(
+            where_line(12.5, 70.2, -3.25, "minecraft:the_nether"),
+            "12, 70, -4 in minecraft:the_nether"
+        );
+    }
+
+    #[test]
+    fn shown_unless_stored_false() {
+        assert!(read_shown(None));
+        assert!(read_shown(Some("true".into())));
+        assert!(!read_shown(Some("false\n".into())));
+        assert_eq!(shown_label(false), "Shown: OFF");
+    }
+}

native/coords-hud/mixins/coords_hud/settings.rs

@@ -0,0 +1,8 @@
+// The mod's settings page: one button, the box shown or hidden.
+fn official_coords_hud_page(game: &mut crate::game::Game<'_>, mod_id: &str, buttons: &mut Vec<String>) {
+    use crate::game::official_coords_hud as m;
+    if mod_id != m::ID {
+        return;
+    }
+    buttons.push(m::shown_label(m::shown(|| game.native_setting(m::ID, "shown"))));
+}

native/coords-hud/proof.py

@@ -0,0 +1,56 @@
+"""Coordinates HUD in a running modded game: its row and settings page in Options > Mods, the box in the top
+left, /coords hiding and showing it (and keeping that), and /where's line in chat (screenshots)."""
+import json
+import time
+from game import Game, difference
+
+DATA = "horizon-mods/.horizon-mod-data/coords_hud"
+TOP_LEFT, CHAT = (0.0, 0.0, 0.25, 0.1), (0.0, 0.7, 0.5, 0.95)
+
+
+def typed(g, line):
+    """As the player types it: T opens the chat box, then the line and Enter."""
+    g.run("key", "t", "tap")
+    time.sleep(0.5)
+    g.run("type", line)
+    g.run("key", "enter", "tap")
+    time.sleep(1)
+
+
+def run(ctl, resources, out):
+    with Game(ctl, resources, out) as g:
+        g.run("options", "mods")
+        assert "Coordinates HUD 2.0.0: ON" in g.labels(), g.labels()
+        g.run("click", g.ids()["Settings"])
+        page = g.labels()
+        assert "Shown: ON" in page, page
+        g.run("click", g.ids()["Shown: ON"])
+        clicked = (g.home / DATA / "shown").read_text()
+        g.run("click", g.ids()["Shown: OFF"])
+        g.play()
+        g.run("command", "tp @s ~ ~ ~ 0 10")
+        time.sleep(2)
+        shown = g.shot("1-shown")
+        typed(g, "/coords")
+        hidden_file = (g.home / DATA / "shown").read_text()
+        time.sleep(4)
+        hidden = g.shot("2-hidden")
+        typed(g, "/coords")
+        typed(g, "/where")
+        where = g.shot("3-where")
+        results = {
+            "page": page,
+            "shown_file_after_click": clicked,
+            "shown_file_after_coords": hidden_file,
+            "shown_file_at_end": (g.home / DATA / "shown").read_text(),
+            "diff_top_left_hidden": round(difference(shown, hidden, TOP_LEFT), 1),
+            "diff_top_left_shown_again": round(difference(shown, where, TOP_LEFT), 1),
+            "diff_chat_where": round(difference(hidden, where, CHAT), 1),
+        }
+        print(json.dumps(results, indent=2))
+        assert clicked == "false" and hidden_file == "false", results
+        assert results["shown_file_at_end"] == "true", results
+        assert results["diff_top_left_hidden"] > 4, results
+        assert results["diff_top_left_shown_again"] < results["diff_top_left_hidden"], results
+        # native_chat lines are the client's; chat-log reads the server's chat here: see 3-where.png.
+        print(json.dumps({"proof": "coords_hud", "ok": True, **results}, indent=2))

native/recipes/compatibility.json

@@ -2,7 +2,7 @@
   "game": "26.3",
   "hooks": 2,
   "horizon_repository": "https://github.com/horizon-rust/horizon",
-  "horizon_revision": "8f91683323ac1165e7d76b3037e18f30fe647205",
+  "horizon_revision": "4baa571566e39bfd6594988d3bb2bc85440c30e7",
   "horizon_mixins_repository": "https://github.com/horizon-rust/horizon-mixins",
   "horizon_mixins_revision": "0d6b103c70633d8fd9443d8d0acd3aadaacedb06"
 }

native/recipes/mixins/recipes/horizon-mixin.toml

@@ -6,7 +6,7 @@ priority = 100
 # The commit it was tested on. It uses only the native hook points (hooks 2 in
 # compatibility.json): the launcher builds it on any Horizon that has them.
 [compatibility]
-horizon_revision = "8f91683323ac1165e7d76b3037e18f30fe647205"
+horizon_revision = "4baa571566e39bfd6594988d3bb2bc85440c30e7"
 
 [[module]]
 id = "runtime"

native/smp/.gitignore

@@ -0,0 +1,2 @@
+__pycache__/
+target/

native/smp/Cargo.lock

@@ -0,0 +1,107 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "horizon-mod-smp"
+version = "0.5.0"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
+[[package]]
+name = "itoa"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
+
+[[package]]
+name = "memchr"
+version = "2.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.107"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "985e7ec9bb745e6ce6535b544d84d6cd6f7ad8bd711c398938ae983b91a766d9"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.47"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fbf4db142a473a8d80c26bbf18454ed458bf8d26c8219c331daecfdbd079001"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "serde"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4148590afebada386688f18773da617792bf2ef03ffc1e4cbd2b1d45b023e0ba"
+dependencies = [
+ "serde_core",
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_core"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67dca2c9c51e58a4791a4b1ed58308b39c64224d349a935ab5039aa360942a48"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7a5d71263a5a7d47b41f6b3f06ba276f10cc18b0931f1799f710578e2309348"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "serde_json"
+version = "1.0.154"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7e9cc8b1b85264074fbcc02a88680c4096b1e47df8f739dceb03bf482f04bd6"
+dependencies = [
+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
+
+[[package]]
+name = "syn"
+version = "3.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d78c8dee4c7bf0e14673097256fed6142ce9d3b85a408189d07482442145823b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2c754d6c33795a1c324727428e5a7dedb5b06195f9890bdbcba760d3e246563"
+
+[[package]]
+name = "zmij"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29666d0abbfad1e3dc4dcf6144730dd3a3ab225bbbdac83319345b1b44ccfc1b"

native/smp/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "horizon-mod-smp"
+version = "0.5.0"
+edition = "2024"
+license = "MIT"
+publish = false
+description = "The official Horizon server's SMP, a native server mod: economy (and next, market, trades, claims)."
+
+# The mod's rules and their tests: the same files the bundle adds to the game
+# (as game::smp_store, game::smp_economy), under the same names.
+[lib]
+path = "src/lib.rs"
+
+[dependencies]
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"

native/smp/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Ludovic Marie and the Horizon contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

native/smp/README.md

@@ -0,0 +1,103 @@
+# SMP (Horizon native server mod)
+
+The official Horizon server's survival layer ([design](https://github.com/horizon-rust/horizon/blob/main/docs/smp.md)).
+It is **not** part of Horizon's own server: only a server that builds this mod into its engine has it. It isn't listed
+in the registry.
+
+Players install nothing: it speaks only what a stock Horizon client already shows (commands with completions, chat
+lines, vanilla chest menus the server fills with ordinary items (the trade menu); later sounds, titles, the action
+bar, boss bars and the sidebar).
+
+This version: the economy, the server market, player trades, the coinflip and the lottery.
+
+| Command | Does |
+|---|---|
+| `/balance [player]`, `/bal` | your balance, or another player's |
+| `/pay <player> <amount>` | gives money to a player who has an account (anyone who has played since the mod was on) |
+| `/baltop [page]` | the richest players, 10 a page |
+| `/eco give\|take\|set <player> <amount>` | operators of level 3: corrections, logged |
+| `/worth [item]` | what the market pays and asks for an item (the one in your hand without a name) |
+| `/sell hand [count]`, `/sell <item> [count]`, `/sell all` | sells to the market: the stack in your hand, an item, or everything it buys |
+| `/buy <item> [count]` | buys from the market, only what fits in your inventory |
+| `/trade <player>` | asks a player to trade (60 s to answer) |
+| `/trade accept [player]`, `/trade deny [player]` | answers a request |
+| `/trade money <amount>` | the money you add to your offer (0: none) |
+| `/trade cancel` | ends your trade, or withdraws your request |
+| `/coinflip <amount> [player]` | stakes an amount for anyone (or one player) to match; off unless `gambling.enabled` |
+| `/lottery`, `/lottery buy <tickets>` | the pot, your tickets and the time to the draw; buys tickets (off unless `gambling.enabled`) |
+| `/coinflip accept <player>`, `/coinflip cancel`, `/coinflip list` | takes an offer (a fair coin decides, the winner gets both stakes), withdraws yours, lists those waiting |
+
+The market trades only plain items (not worn, named or enchanted), and only with players in survival or adventure
+mode. Items move first, then money, both logged; a sale the log refuses gives the items back, and a purchase checks the
+money and the room before anything moves.
+
+**Trades.** Once accepted, both players see a 6-row chest menu: their own offer on the left (16 stacks), the other's
+on the right, each side's money, their confirm and cancel buttons, and whether the other has confirmed. A click on a
+stack in your inventory, below the menu, adds it to your offer; a click on it in your offer takes it back. The menu
+moves nothing: offered stacks stay in their owners' inventories, the menu shows copies, and a stack that changes
+(used, dropped, grown by a pickup) leaves the offer. Any change clears both confirmations. When both have confirmed,
+the server checks that each still holds exactly what they offer, has room for what they get and has the money, logs
+the trade, and swaps everything in one step, or nothing (and both must confirm again). Closing the menu,
+`/trade cancel`, leaving, dying or the other player leaving ends the trade with nothing moved. Survival and
+adventure players only.
+
+**Coinflips.** Off by default: the owner turns them on in `config.json` (`gambling`: `enabled`, `min_bet` 10,
+`max_bet` 1000, `cooldown_seconds` 30, `offer_seconds` 60, `fee_percent` 0). A stake is held from the offer, in
+`economy.json` with the balances, until the coin falls; an offer cancelled, not taken in time, or whose player
+left gives it back, and so does the next start for one the server stopped with. The coin is a fresh random key from
+the system, never the world's random. Only the in-game currency is staked and won.
+
+**The lottery.** Part of `gambling` (`ticket_price` 10, `max_tickets` 100 a player a draw, `lottery_seconds` 3600
+from a round's first ticket to its draw). Tickets are held like coinflip stakes; at the draw one ticket is picked at
+random among all sold (more tickets, more chances), its owner gets the pot (less `fee_percent`), and everyone hears
+it. A round with a single player, or one the server stopped with, gives every ticket back.
+
+The currency is earned in game only: it can't be bought with real money or cashed out (Mojang's usage guidelines).
+
+## Data
+
+Everything is in the world's folder, `world/horizon-smp/`, so a backup of the world carries it. A world without that
+folder is untouched until the mod first runs on it; it changes no block and no player.
+
+| File | Holds |
+|---|---|
+| `config.json` | `currency` (default `coins`), `starting_balance` (default 0), and `market`: `enabled` and `items`, each item's `buy` (what the market asks) and `sell` (what it pays), 0 closing that side; written with the defaults the first time, and again when a newer version adds keys (your values kept) |
+| `economy.json` | balances by player UUID, with the name last seen, and `held`: coinflip stakes and lottery tickets being decided |
+| `audit.log` | one JSON line per change, written before the change: `time` (ms), `kind` (`open`, `pay`, `eco_give`...), `amount`, `from`/`to` with their balance before, `by` for an operator; a trade's line (`trade`: both players, their items and money) comes before its swap, `trade_failed` after one that didn't go through |
+
+`economy.json` is written whole to a temporary file, flushed and renamed over the old one, at most once a server tick
+and when the world closes: a crash leaves the old file or the new one. If it can't be read, the economy stays off (the
+commands say so) rather than start from nothing.
+
+## Made on the hook points
+
+It hooks only Horizon's native hook points: `native_register_commands` and `native_perform_command` (API 8), the
+acting player's items (API 9), the server menus and `native_exchange_items` (API 10), the server tick and the world
+lifecycle. `compatibility.json` names `"hooks": 10`.
+
+| File | What it is |
+|---|---|
+| `mixins/smp/horizon-mixin.toml` | The bundle: seven modules and the HEAD hooks |
+| `mixins/smp/smp_store.rs`, `smp_economy.rs`, `smp_market.rs`, `smp_trade.rs`, `smp_games.rs`, `smp_lottery.rs` | The rules, no game types (a trade's stacks are a type parameter): added to the game as `game::smp_store`, `game::smp_economy`, `game::smp_market`, `game::smp_trade`, `game::smp_games`, `game::smp_lottery`; also this crate's modules (`src/lib.rs`), for their tests |
+| `mixins/smp/glue.rs` | The state for the open world and the edges to the game's types (`game::smp_glue`) |
+| `mixins/smp/{register,command,tick,lifecycle,menu_clicked,menu_closed}.rs` | One small helper per hook |
+| `proof.py` | A dedicated server built with the mod and two real clients, on fresh temporary data |
+
+## Build and prove
+
+```sh
+(cd native/smp && cargo test)                          # the rules
+python3 native/tools/native.py check smp               # apply on the tested Horizon and cargo check the game
+python3 native/tools/native.py proof smp --resources /path/to/.local/horizon-client/26.3
+```
+
+## The official server's engine
+
+The server runs `horizon-server` as usual, with `[engine] path` pointing at a game built with this mod:
+
+```sh
+NATIVE_NO_DEFAULT_FEATURES=1 python3 native/tools/native.py build smp --horizon <the release's commit>
+```
+
+prints the built `horizon-client` (`--no-default-features`: the server build, without audio and controllers). When
+to deploy it on the official server is the owners' decision.

native/smp/compatibility.json

@@ -0,0 +1,8 @@
+{
+  "game": "26.3",
+  "hooks": 10,
+  "horizon_repository": "https://github.com/horizon-rust/horizon",
+  "horizon_revision": "f533c3af7d41d7ecc3b015a9fbb0dbf5eb64ae26",
+  "horizon_mixins_repository": "https://github.com/horizon-rust/horizon-mixins",
+  "horizon_mixins_revision": "0d6b103c70633d8fd9443d8d0acd3aadaacedb06"
+}

native/smp/mixins/smp/command.rs

@@ -0,0 +1,11 @@
+// A player's command on the server: the SMP's own, when it is one.
+fn smp_perform_command(
+    game: &mut crate::game::Game<'_>,
+    player: &crate::game::native_server::NativeServerPlayer,
+    command: &str,
+    ran: &mut bool,
+) {
+    if !*ran {
+        crate::game::smp_glue::perform(game, player, command, ran);
+    }
+}

native/smp/mixins/smp/glue.rs

@@ -0,0 +1,573 @@
+// The SMP in the server's game: its state for the open world, and the edges
+// between the game's types and the rules (smp_economy, smp_market,
+// smp_trade, smp_games, smp_lottery). Added to
+// the game as `game::smp_glue`; the helpers (register.rs, command.rs,
+// tick.rs, lifecycle.rs, menu_clicked.rs, menu_closed.rs) call it from the
+// hook points.
+
+use crate::game::{
+    Game,
+    native_server::{NativeCommand, NativeServerPlayer},
+    smp_economy::{self, Economy, Out, Player},
+    smp_games::{self, Games},
+    smp_lottery::Lottery,
+    native_menus::native_menu_inventory_slot,
+    smp_market::{self, Bag, Market},
+    smp_store,
+    smp_trade::{self, Act, Cell, Trades},
+};
+use horizon_client::{
+    items::ItemStack,
+    lan::data::component_nbt,
+    text::{self, Text},
+};
+use std::{path::PathBuf, sync::Mutex};
+
+/// The mod's id, name and version.
+pub const ID: &str = "smp";
+pub const NAME: &str = "SMP";
+pub const VERSION: &str = "0.5.0";
+
+/// `config.json` in `world/horizon-smp/`, written with its defaults the
+/// first time, and again with the keys a newer version adds (values kept).
+#[derive(Clone, Debug, Default, serde::Serialize, serde::Deserialize)]
+#[serde(default)]
+pub struct Config {
+    #[serde(flatten)]
+    pub economy: smp_economy::Config,
+    pub market: smp_market::Config,
+    pub gambling: smp_games::Config,
+}
+
+/// The SMP of the open world.
+pub struct Smp {
+    dir: PathBuf,
+    /// An error when `economy.json` can't be read: the commands say so.
+    economy: Result<Economy, String>,
+    market: Market,
+    trades: Trades<ItemStack>,
+    games: Games,
+    lottery: Lottery,
+}
+
+static STATE: Mutex<Option<Smp>> = Mutex::new(None);
+static TICKS: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
+
+fn open(dir: PathBuf) -> Smp {
+    let config_path = dir.join("config.json");
+    let (config, write) = match smp_store::read_json::<Option<serde_json::Value>>(&config_path) {
+        // No file yet: the defaults, written for the owner to edit.
+        Ok(None) => (Config::default(), true),
+        Ok(Some(v)) => match serde_json::from_value::<Config>(v.clone()) {
+            // Written again only when a newer version adds keys; values kept.
+            Ok(c) => {
+                let keys = |v: &serde_json::Value| v.as_object().map(|o| o.len());
+                let full = serde_json::to_value(&c).unwrap_or_default();
+                let added = keys(&full) != keys(&v);
+                (c, added)
+            }
+            Err(e) => {
+                log::error!(
+                    "[smp] {}: {e}: the defaults are used",
+                    config_path.display()
+                );
+                (Config::default(), false)
+            }
+        },
+        // A damaged file stays as it is for the owner to mend.
+        Err(e) => {
+            log::error!("[smp] {e}: the defaults are used");
+            (Config::default(), false)
+        }
+    };
+    if write && let Err(e) = smp_store::write_json(&config_path, &config) {
+        log::error!("[smp] {e}");
+    }
+    log::info!("[smp] {NAME} {VERSION} on {}", dir.display());
+    let economy = Economy::open(&dir, config.economy);
+    if let Err(e) = &economy {
+        log::error!("[smp] the economy is off: {e}");
+    }
+    Smp {
+        dir,
+        economy,
+        market: Market {
+            config: config.market,
+        },
+        trades: Trades::default(),
+        games: Games::new(config.gambling),
+        lottery: Lottery::default(),
+    }
+}
+
+/// The SMP's state, opened for the world in `dir` on first use (the files
+/// of another world it held are written first).
+fn state(dir: PathBuf) -> std::sync::MutexGuard<'static, Option<Smp>> {
+    let mut state = STATE.lock().unwrap_or_else(|e| e.into_inner());
+    if state.as_ref().is_none_or(|s| s.dir != dir) {
+        if let Some(old) = state.as_mut() {
+            save(old);
+        }
+        *state = Some(open(dir));
+    }
+    if let Some(Ok(e)) = state.as_mut().map(|s| &mut s.economy) {
+        e.now = chrono::Utc::now().timestamp_millis();
+    }
+    state
+}
+
+fn save(smp: &mut Smp) {
+    if let Ok(e) = &mut smp.economy
+        && let Err(err) = e.save()
+    {
+        log::error!("[smp] {err}");
+    }
+}
+
+/// The commands, for every player's command tree.
+pub fn commands(commands: &mut Vec<NativeCommand>) {
+    for usage in [
+        "balance [player:word]",
+        "bal [player:word]",
+        "pay <player:word> <amount:integer>",
+        "baltop [page:integer]",
+        "worth [item:item]",
+        "sell hand [count:integer]",
+        "sell all",
+        "sell <item:item> [count:integer]",
+        "buy <item:item> [count:integer]",
+        "trade <player:word>",
+        "trade accept [player:word]",
+        "trade deny [player:word]",
+        "trade cancel",
+        "trade money <amount:integer>",
+        "coinflip <amount:integer> [player:word]",
+        "coinflip accept <player:word>",
+        "coinflip cancel",
+        "coinflip list",
+        "lottery",
+        "lottery buy <tickets:integer>",
+    ] {
+        commands.push(NativeCommand::new(usage));
+    }
+    for verb in ["give", "take", "set"] {
+        commands.push(NativeCommand::op(
+            &format!("eco {verb} <player:word> <amount:integer>"),
+            3,
+        ));
+    }
+}
+
+/// The acting player's items (inside `native_perform_command`).
+struct GameBag<'a, 'g>(&'a mut Game<'g>);
+
+impl Bag for GameBag<'_, '_> {
+    fn held(&self) -> Option<(String, u32, bool)> {
+        self.0.native_held()
+    }
+    fn carried(&self) -> Vec<(String, u32)> {
+        self.0.native_carried_items()
+    }
+    fn count(&mut self, item: &str) -> u32 {
+        self.0.native_count_items(item)
+    }
+    fn take(&mut self, item: &str, count: u32) -> u32 {
+        self.0.native_take_items(item, count)
+    }
+    fn room(&mut self, item: &str) -> u32 {
+        self.0.native_room_for(item)
+    }
+    fn give(&mut self, item: &str, count: u32) -> u32 {
+        self.0.native_give_items(item, count)
+    }
+}
+
+const COMMANDS: [&str; 11] = [
+    "balance", "bal", "pay", "baltop", "eco", "worth", "sell", "buy", "trade", "coinflip", "lottery",
+];
+
+/// A random number below `n` (n > 0), never the world's random: a fresh
+/// SipHash key (seeded from the system's randomness) over the time.
+fn below(n: u64) -> u64 {
+    use std::hash::BuildHasher;
+    let time = std::time::SystemTime::now();
+    std::collections::hash_map::RandomState::new().hash_one(time) % n.max(1)
+}
+
+/// A fair coin, never the world's random: a fresh SipHash key (seeded from
+/// the system's randomness) over the time.
+fn heads() -> bool {
+    use std::hash::BuildHasher;
+    let time = std::time::SystemTime::now();
+    std::collections::hash_map::RandomState::new().hash_one(time) & 1 == 1
+}
+
+/// A player's command.
+pub(in crate::game) fn perform(
+    game: &mut Game<'_>,
+    player: &NativeServerPlayer,
+    line: &str,
+    ran: &mut bool,
+) {
+    if !game.native_on(ID) || !COMMANDS.contains(&line.split(' ').next().unwrap_or_default()) {
+        return;
+    }
+    let Some(dir) = game.native_world_dir() else {
+        return;
+    };
+    let me = Player {
+        uuid: player.uuid,
+        name: player.name.clone(),
+        level: player.permission,
+    };
+    // Survival and adventure: a creative player could sell what they made.
+    let trades = matches!(player.game_mode, 0 | 2);
+    let players = game.native_server_players();
+    let online = |name: &str| {
+        players
+            .iter()
+            .find(|p| p.name.eq_ignore_ascii_case(name))
+            .map(|p| (p.uuid, p.name.clone(), matches!(p.game_mode, 0 | 2)))
+    };
+    let now = chrono::Utc::now().timestamp_millis();
+    let mut guard = state(dir.join(smp_store::DIR));
+    let smp = guard.as_mut().expect("opened");
+    let mut acts = Vec::new();
+    let out = match &mut smp.economy {
+        Ok(e) => {
+            e.seen(me.uuid, &me.name);
+            let mut bag = GameBag(game);
+            e.command(&me, line)
+                .or_else(|| smp.market.command(e, &me, trades, &mut bag, line))
+                .or_else(|| {
+                    let (out, a) = smp.trades.command(e, &me, trades, &online, now, line)?;
+                    acts = a;
+                    Some(out)
+                })
+                .or_else(|| {
+                    let named = |n: &str| online(n).map(|(u, name, _)| (u, name));
+                    smp.games.command(e, &me, &named, now, &mut heads, line)
+                })
+                .or_else(|| smp.lottery.command(&smp.games.config, e, &me, now, line))
+                .unwrap_or_default()
+        }
+        Err(_) => vec![Out::Error(
+            "The economy is off: its file can't be read (see the server log).".into(),
+        )],
+    };
+    act(game, smp, acts);
+    drop(guard);
+    *ran = true;
+    show(game, out);
+}
+
+/// An item named `name` (not in italics, as a name the game gives).
+fn button(item: &str, name: &str, color: &str) -> ItemStack {
+    let mut stack = ItemStack {
+        item: item.into(),
+        count: 1,
+        damage: 0,
+        extra: None,
+    };
+    let title = serde_json::json!({ "text": name, "italic": false, "color": color });
+    stack.data_mut().custom_name = Some(component_nbt(&title));
+    stack
+}
+
+/// The trade menu's cells as items.
+fn menu_items(smp: &Smp, uuid: u128) -> Vec<Option<ItemStack>> {
+    let money = |n| match &smp.economy {
+        Ok(e) => e.money(n),
+        Err(_) => n.to_string(),
+    };
+    smp.trades
+        .layout(uuid)
+        .into_iter()
+        .map(|cell| match cell {
+            Cell::Empty => None,
+            Cell::Stack(s) => Some(s),
+            Cell::Divider => Some(button("minecraft:gray_stained_glass_pane", " ", "gray")),
+            Cell::Money(true, n) => Some(button(
+                "minecraft:gold_ingot",
+                &format!("Your money: {} (/trade money <amount>)", money(n)),
+                "gold",
+            )),
+            Cell::Money(false, n) => Some(button(
+                "minecraft:gold_ingot",
+                &format!("Their money: {}", money(n)),
+                "gold",
+            )),
+            Cell::Confirm(false) => Some(button(
+                "minecraft:lime_stained_glass_pane",
+                "Confirm the trade",
+                "green",
+            )),
+            Cell::Confirm(true) => Some(button(
+                "minecraft:lime_concrete",
+                "Confirmed (click to take it back)",
+                "green",
+            )),
+            Cell::Cancel => Some(button(
+                "minecraft:red_stained_glass_pane",
+                "Cancel the trade",
+                "red",
+            )),
+            Cell::Other(name, true) => Some(button(
+                "minecraft:lime_concrete",
+                &format!("{name} confirmed"),
+                "green",
+            )),
+            Cell::Other(name, false) => Some(button(
+                "minecraft:gray_concrete",
+                &format!("{name} has not confirmed"),
+                "gray",
+            )),
+        })
+        .collect()
+}
+
+/// Carries out what the trade rules ask.
+fn act(game: &mut Game<'_>, smp: &mut Smp, acts: Vec<Act>) {
+    for a in acts {
+        match a {
+            Act::Show(uuid) => {
+                let items = menu_items(smp, uuid);
+                let Some(t) = smp.trades.open.iter_mut().find(|t| t.side_of(uuid).is_some()) else {
+                    continue;
+                };
+                let me = t.side_of(uuid).expect("found");
+                if t.sides[me].window.is_some() {
+                    game.native_set_menu_items(uuid, items);
+                } else {
+                    let title = Text::literal(format!("Trade with {}", t.sides[1 - me].name));
+                    t.sides[me].window = game.native_open_menu(uuid, smp_trade::ROWS, title, items);
+                }
+            }
+            Act::Close(uuid) => game.native_close_menu(uuid),
+            Act::Settle(uuid) => settle(game, smp, uuid),
+        }
+    }
+}
+
+/// Both confirmed: the trade is logged, then both offers swap in one step
+/// with the money, or nothing moves and both are told why.
+fn settle(game: &mut Game<'_>, smp: &mut Smp, uuid: u128) {
+    let Some(t) = smp.trades.trade_of(uuid).cloned() else {
+        return;
+    };
+    let [a, b] = &t.sides;
+    let players = game.native_server_players();
+    let may = |u: u128| players.iter().any(|p| p.uuid == u && matches!(p.game_mode, 0 | 2));
+    let Ok(economy) = &mut smp.economy else {
+        return;
+    };
+    let fail = |why: String| -> Vec<Out> {
+        t.sides
+            .iter()
+            .map(|s| Out::Tell(s.uuid, format!("The trade didn't go through: {why}.")))
+            .collect()
+    };
+    let stacks = |side: &smp_trade::Side<ItemStack>| -> serde_json::Value {
+        side.offer
+            .iter()
+            .map(|(_, s)| serde_json::json!({ "item": &*s.item, "count": s.count, "plain": s.damage == 0 && s.extra.is_none() }))
+            .collect()
+    };
+    let out = if !may(a.uuid) || !may(b.uuid) {
+        fail("both must be here, in survival or adventure mode".into())
+    } else if economy.balance(a.uuid) < a.money || economy.balance(b.uuid) < b.money {
+        fail("one of you no longer has the money offered".into())
+    } else if let Err(e) = economy.record(serde_json::json!({
+        "kind": "trade",
+        "a": smp_store::uuid_string(a.uuid), "a_items": stacks(a), "a_money": a.money,
+        "b": smp_store::uuid_string(b.uuid), "b_items": stacks(b), "b_money": b.money,
+    })) {
+        fail(e)
+    } else if let Err(e) = game.native_exchange_items(a.uuid, &a.offer, b.uuid, &b.offer) {
+        let _ = economy.record(serde_json::json!({ "kind": "trade_failed", "why": &e }));
+        fail(e)
+    } else {
+        // The balances were checked above: only the log could refuse now.
+        let net = a.money - b.money;
+        let paid = match net.signum() {
+            1 => economy.transfer("trade_money", a.uuid, b.uuid, net),
+            -1 => economy.transfer("trade_money", b.uuid, a.uuid, -net),
+            _ => Ok(()),
+        };
+        if let Err(e) = paid {
+            log::error!("[smp] a trade's money: {e}");
+        }
+        let (_, acts) = smp.trades.end(uuid, "");
+        // Ended as a success: the menus close, with their own line.
+        for act in acts {
+            if let Act::Close(u) = act {
+                game.native_close_menu(u);
+            }
+        }
+        let line = |me: &smp_trade::Side<ItemStack>, them: &smp_trade::Side<ItemStack>| {
+            Out::Tell(
+                me.uuid,
+                format!("Trade with {} done: you gave {} stack(s), got {}.", them.name, me.offer.len(), them.offer.len()),
+            )
+        };
+        show(game, vec![line(a, b), line(b, a)]);
+        return;
+    };
+    // Not settled: both must confirm again.
+    if let Some(t) = smp.trades.open.iter_mut().find(|t| t.side_of(uuid).is_some()) {
+        for s in &mut t.sides {
+            s.confirmed = false;
+        }
+    }
+    act(game, smp, vec![Act::Show(a.uuid), Act::Show(b.uuid)]);
+    show(game, out);
+}
+
+/// A click in a native menu: a trade's, when it is one.
+pub(in crate::game) fn menu_clicked(game: &mut Game<'_>, uuid: u128, window: i32, slot: i32, mode: i32) {
+    // A plain click or a shift-click; drags and double clicks are ignored.
+    if !game.native_on(ID) || !matches!(mode, 0 | 1) {
+        return;
+    }
+    let Some(dir) = game.native_world_dir() else {
+        return;
+    };
+    let mut guard = state(dir.join(smp_store::DIR));
+    let smp = guard.as_mut().expect("opened");
+    let Some(t) = smp.trades.trade_of(uuid) else {
+        return;
+    };
+    let me = t.side_of(uuid).expect("found");
+    if t.sides[me].window != Some(window) {
+        return;
+    }
+    let (out, acts) = match native_menu_inventory_slot(smp_trade::SIZE, slot) {
+        Some(i) => match game.native_player_stacks(uuid).and_then(|s| s.get(i).cloned().flatten()) {
+            Some(stack) => smp.trades.click(uuid, None, Some((i, stack))),
+            None => (Vec::new(), Vec::new()),
+        },
+        None => match usize::try_from(slot).ok().filter(|&s| s < smp_trade::SIZE) {
+            Some(s) => smp.trades.click(uuid, Some(s), None),
+            None => (Vec::new(), Vec::new()),
+        },
+    };
+    act(game, smp, acts);
+    drop(guard);
+    show(game, out);
+}
+
+/// A native menu closed: a trade's ends, nothing moved.
+pub(in crate::game) fn menu_closed(game: &mut Game<'_>, uuid: u128, window: i32) {
+    if !game.native_on(ID) {
+        return;
+    }
+    let Some(dir) = game.native_world_dir() else {
+        return;
+    };
+    let mut guard = state(dir.join(smp_store::DIR));
+    let smp = guard.as_mut().expect("opened");
+    let Some(t) = smp.trades.trade_of(uuid) else {
+        return;
+    };
+    let me = t.side_of(uuid).expect("found");
+    if t.sides[me].window != Some(window) {
+        return;
+    }
+    let why = format!("{} closed the trade", t.sides[me].name);
+    let (out, acts) = smp.trades.end(uuid, &why);
+    act(game, smp, acts);
+    drop(guard);
+    show(game, out);
+}
+
+fn show(game: &mut Game<'_>, out: Vec<Out>) {
+    for o in out {
+        match o {
+            Out::Reply(s) => game.native_feedback(Text::literal(s)),
+            Out::Error(s) => game.native_feedback(Text::literal(s).with_color(text::RED)),
+            Out::Tell(uuid, s) => {
+                game.native_tell(uuid, Text::literal(s).with_color(text::GOLD));
+            }
+            Out::All(s) => game.native_broadcast(Text::literal(s).with_color(text::GOLD)),
+        }
+    }
+}
+
+/// The end of each server tick: accounts for the players on (once a second)
+/// and the files that changed.
+pub(in crate::game) fn tick(game: &mut Game<'_>) {
+    let Some(dir) = game.native_world_dir() else {
+        return;
+    };
+    let n = TICKS.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+    let players = if n % 20 == 0 {
+        game.native_server_players()
+    } else {
+        Vec::new()
+    };
+    let mut guard = state(dir.join(smp_store::DIR));
+    let smp = guard.as_mut().expect("opened");
+    let mut out = Vec::new();
+    if let Ok(e) = &mut smp.economy
+        && n % 20 == 0
+    {
+        for p in &players {
+            e.seen(p.uuid, &p.name);
+        }
+        // Once a second: coinflips nobody took, and those of players gone.
+        out.extend(smp.games.expire(e, chrono::Utc::now().timestamp_millis()));
+        let gone: Vec<u128> = smp
+            .games
+            .offers
+            .iter()
+            .map(|o| o.from)
+            .filter(|u| !players.iter().any(|p| p.uuid == *u))
+            .collect();
+        for uuid in gone {
+            smp.games.left(e, uuid);
+        }
+        let now = chrono::Utc::now().timestamp_millis();
+        out.extend(smp.lottery.tick(&smp.games.config, e, now, &mut below));
+    }
+    // Each trade's offers against the inventories now: a player gone or
+    // dead ends it; a stack that changed leaves its offer.
+    let sides: Vec<(u128, String)> = smp
+        .trades
+        .open
+        .iter()
+        .flat_map(|t| t.sides.iter().map(|s| (s.uuid, s.name.clone())))
+        .collect();
+    for (uuid, name) in sides {
+        match game.native_player_stacks(uuid) {
+            None => {
+                let (o, acts) = smp.trades.end(uuid, &format!("{name} is gone"));
+                out.extend(o);
+                act(game, smp, acts);
+            }
+            Some(stacks) if smp.trades.refresh(uuid, &stacks) => {
+                let other = smp.trades.trade_of(uuid).and_then(|t| {
+                    t.sides.iter().find(|s| s.uuid != uuid).map(|s| s.uuid)
+                });
+                act(game, smp, vec![Act::Show(uuid)]);
+                if let Some(o) = other {
+                    act(game, smp, vec![Act::Show(o)]);
+                    out.push(Out::Tell(o, format!("{name}'s offer changed.")));
+                }
+                out.push(Out::Tell(uuid, "A stack you offered changed: it left your offer.".into()));
+            }
+            Some(_) => {}
+        }
+    }
+    save(smp);
+    drop(guard);
+    show(game, out);
+}
+
+/// The world closed: its files are written and its state let go.
+pub fn closed() {
+    let mut state = STATE.lock().unwrap_or_else(|e| e.into_inner());
+    if let Some(smp) = state.as_mut() {
+        save(smp);
+    }
+    *state = None;
+}

native/smp/mixins/smp/horizon-mixin.toml

@@ -0,0 +1,115 @@
+[mod]
+id = "smp"
+version = "0.5.0"
+priority = 100
+
+# The commit of horizon main it was tested on. It uses only the native hook points (hooks 10 in
+# compatibility.json): it builds on any Horizon that has them.
+[compatibility]
+horizon_revision = "f533c3af7d41d7ecc3b015a9fbb0dbf5eb64ae26"
+
+[[module]]
+id = "store"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_store"
+source = "smp_store.rs"
+
+[[module]]
+id = "economy"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_economy"
+source = "smp_economy.rs"
+
+[[module]]
+id = "market"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_market"
+source = "smp_market.rs"
+
+[[module]]
+id = "trade"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_trade"
+source = "smp_trade.rs"
+
+[[module]]
+id = "games"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_games"
+source = "smp_games.rs"
+
+[[module]]
+id = "lottery"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_lottery"
+source = "smp_lottery.rs"
+
+[[module]]
+id = "glue"
+file = "crates/horizon-client/src/game.rs"
+name = "smp_glue"
+source = "glue.rs"
+
+[[injection]]
+id = "register"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_register_commands"
+helper = "register.rs"
+bindings = [
+  { name = "commands", ty = "&mut Vec<crate::game::native_server::NativeCommand>", value = "&mut *commands" },
+]
+
+[[injection]]
+id = "command"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_perform_command"
+helper = "command.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "player", ty = "&crate::game::native_server::NativeServerPlayer", value = "player" },
+  { name = "command", ty = "&str", value = "command" },
+  { name = "ran", ty = "&mut bool", value = "&mut *ran" },
+]
+
+[[injection]]
+id = "tick"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_server_tick"
+helper = "tick.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "phase", ty = "crate::game::native_lifecycle::ServerTickPhase", value = "phase" },
+]
+
+[[injection]]
+id = "lifecycle"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_world_lifecycle"
+helper = "lifecycle.rs"
+bindings = [
+  { name = "phase", ty = "crate::game::native_lifecycle::WorldPhase", value = "phase" },
+]
+
+[[injection]]
+id = "menu_clicked"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_menu_clicked"
+helper = "menu_clicked.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "uuid", ty = "u128", value = "uuid" },
+  { name = "window", ty = "i32", value = "window" },
+  { name = "slot", ty = "i32", value = "slot" },
+  { name = "mode", ty = "i32", value = "mode" },
+]
+
+[[injection]]
+id = "menu_closed"
+kind = "HEAD"
+target = "horizon_client::game::native_hooks::Game<'_>::native_menu_closed"
+helper = "menu_closed.rs"
+bindings = [
+  { name = "game", ty = "&mut crate::game::Game<'_>", value = "&mut *self" },
+  { name = "uuid", ty = "u128", value = "uuid" },
+  { name = "window", ty = "i32", value = "window" },
+]

native/smp/mixins/smp/lifecycle.rs

@@ -0,0 +1,10 @@
+// The world closing: the SMP writes its files and lets its state go.
+fn smp_world_lifecycle(phase: crate::game::native_lifecycle::WorldPhase) {
+    use crate::game::native_lifecycle::WorldPhase;
+    if matches!(
+        phase,
+        WorldPhase::WorldCloseFinal | WorldPhase::WorldCloseFailed
+    ) {
+        crate::game::smp_glue::closed();
+    }
+}

native/smp/mixins/smp/menu_clicked.rs

@@ -0,0 +1,4 @@
+// A click in a menu a native mod opened: the SMP's trade menu, when it is one.
+fn smp_menu_clicked(game: &mut crate::game::Game<'_>, uuid: u128, window: i32, slot: i32, mode: i32) {
+    crate::game::smp_glue::menu_clicked(game, uuid, window, slot, mode);
+}

native/smp/mixins/smp/menu_closed.rs

@@ -0,0 +1,4 @@
+// A menu a native mod opened closed: a trade's ends, nothing moved.
+fn smp_menu_closed(game: &mut crate::game::Game<'_>, uuid: u128, window: i32) {
+    crate::game::smp_glue::menu_closed(game, uuid, window);
+}

native/smp/mixins/smp/register.rs

@@ -0,0 +1,4 @@
+// The SMP's commands in every player's command tree.
+fn smp_register_commands(commands: &mut Vec<crate::game::native_server::NativeCommand>) {
+    crate::game::smp_glue::commands(commands);
+}

native/smp/mixins/smp/smp_economy.rs

@@ -0,0 +1,684 @@
+// The SMP's economy: one currency, a balance per player UUID
+// (`economy.json`), and the commands `/balance`, `/pay`, `/baltop` and the
+// operators' `/eco`. Every change is written to the audit log first, then
+// made; a change the log refuses is not made. No game types: the glue
+// (glue.rs) hands in the player and the line, and sends back what this
+// answers. Added to the game as `game::smp_economy`; also a module of this
+// crate, for its tests.
+
+use super::smp_store::{Audit, read_json, uuid_string, write_json};
+use serde::{Deserialize, Serialize};
+use std::{collections::BTreeMap, path::PathBuf};
+
+/// Amounts above this are refused: far beyond any economy, far below overflow.
+pub const MAX_AMOUNT: i64 = 1_000_000_000_000;
+/// Lines of `/baltop` a page.
+pub const PAGE: usize = 10;
+
+/// `config.json`'s economy settings.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Config {
+    /// Shown after amounts: `1,250 coins`.
+    pub currency: String,
+    /// What a new account holds.
+    pub starting_balance: i64,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            currency: "coins".into(),
+            starting_balance: 0,
+        }
+    }
+}
+
+/// One player's account.
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct Account {
+    /// The name last seen.
+    pub name: String,
+    pub balance: i64,
+}
+
+/// `economy.json`.
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct Accounts {
+    /// By UUID, as `uuid_string` writes it.
+    pub accounts: BTreeMap<String, Account>,
+    /// Money held for a game being decided (a coinflip's stake), by UUID:
+    /// in the same file as the balances, so a crash can't lose it or count
+    /// it twice. Given back when the economy opens (a restart voids games).
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    pub held: BTreeMap<String, i64>,
+}
+
+/// A player as a command sees them.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Player {
+    pub uuid: u128,
+    pub name: String,
+    /// Operator level, 0 to 4.
+    pub level: u8,
+}
+
+/// What a command answers: its feedback, red when an error, and lines to
+/// other players.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Out {
+    Reply(String),
+    Error(String),
+    Tell(u128, String),
+    /// A line to every player (and the server's log).
+    All(String),
+}
+
+pub struct Economy {
+    pub config: Config,
+    accounts: Accounts,
+    path: PathBuf,
+    audit: Audit,
+    dirty: bool,
+    /// Milliseconds since 1970, for the log (the glue sets it each call).
+    pub now: i64,
+}
+
+impl Economy {
+    /// The economy kept in `dir` (`world/horizon-smp/`); an error when
+    /// `economy.json` exists and can't be read: the economy then stays off
+    /// rather than start from nothing.
+    pub fn open(dir: &std::path::Path, config: Config) -> Result<Self, String> {
+        let path = dir.join("economy.json");
+        let accounts = read_json(&path)?;
+        let mut economy = Self {
+            config,
+            accounts,
+            path,
+            audit: Audit::new(dir.join("audit.log")),
+            dirty: false,
+            now: 0,
+        };
+        // Games the last run left undecided: their stakes go back.
+        let held: Vec<(String, i64)> = economy.accounts.held.clone().into_iter().collect();
+        for (key, amount) in held {
+            if let Some(uuid) = super::smp_store::parse_uuid(&key) {
+                economy.release("held_returned", uuid, amount)?;
+            }
+        }
+        Ok(economy)
+    }
+
+    /// Money `uuid` has held for a game.
+    pub fn held(&self, uuid: u128) -> i64 {
+        self.accounts
+            .held
+            .get(&uuid_string(uuid))
+            .copied()
+            .unwrap_or(0)
+    }
+
+    /// Moves `amount` of `uuid`'s balance to held, logged as `kind`.
+    pub fn hold(&mut self, kind: &str, uuid: u128, amount: i64) -> Result<(), String> {
+        let key = uuid_string(uuid);
+        let balance = self.balance(uuid);
+        if amount <= 0 || amount > MAX_AMOUNT {
+            return Err("The amount must be a positive whole number.".into());
+        }
+        if !self.accounts.accounts.contains_key(&key) {
+            return Err("No such account.".into());
+        }
+        if balance < amount {
+            return Err(format!("You only have {}.", self.money(balance)));
+        }
+        let entry = self.entry(kind, Some(uuid), None, amount, "");
+        self.audit.append(&entry)?;
+        self.accounts
+            .accounts
+            .get_mut(&key)
+            .expect("checked")
+            .balance -= amount;
+        *self.accounts.held.entry(key).or_default() += amount;
+        self.dirty = true;
+        Ok(())
+    }
+
+    /// Gives back up to `amount` of what `uuid` has held, logged as `kind`.
+    pub fn release(&mut self, kind: &str, uuid: u128, amount: i64) -> Result<(), String> {
+        let key = uuid_string(uuid);
+        let amount = amount.min(self.held(uuid));
+        if amount <= 0 {
+            return Ok(());
+        }
+        let entry = self.entry(kind, None, Some(uuid), amount, "");
+        self.audit.append(&entry)?;
+        self.take_held(&key, amount);
+        let account = self.accounts.accounts.entry(key).or_default();
+        account.balance = account.balance.saturating_add(amount);
+        self.dirty = true;
+        Ok(())
+    }
+
+    /// A game decided: each stake leaves held, and `winner` gets `prize`
+    /// (at most the stakes together), logged as `kind`.
+    pub fn award(
+        &mut self,
+        kind: &str,
+        stakes: &[(u128, i64)],
+        winner: u128,
+        prize: i64,
+    ) -> Result<(), String> {
+        let total: i64 = stakes.iter().map(|(_, a)| *a).sum();
+        if stakes.iter().any(|(u, a)| self.held(*u) < *a) || !(0..=total).contains(&prize) {
+            return Err("The stakes are not held.".into());
+        }
+        let mut entry = self.entry(kind, None, Some(winner), prize, "");
+        entry["stakes"] = stakes
+            .iter()
+            .map(|(u, a)| serde_json::json!({ "uuid": uuid_string(*u), "amount": a }))
+            .collect();
+        self.audit.append(&entry)?;
+        for (u, a) in stakes {
+            self.take_held(&uuid_string(*u), *a);
+        }
+        let account = self
+            .accounts
+            .accounts
+            .entry(uuid_string(winner))
+            .or_default();
+        account.balance = account.balance.saturating_add(prize);
+        self.dirty = true;
+        Ok(())
+    }
+
+    fn take_held(&mut self, key: &str, amount: i64) {
+        if let Some(h) = self.accounts.held.get_mut(key) {
+            *h -= amount;
+            if *h <= 0 {
+                self.accounts.held.remove(key);
+            }
+        }
+    }
+
+    /// Writes `economy.json` when it changed (end of a tick, world closing).
+    pub fn save(&mut self) -> Result<(), String> {
+        self.audit.sync();
+        if !self.dirty {
+            return Ok(());
+        }
+        write_json(&self.path, &self.accounts)?;
+        self.dirty = false;
+        Ok(())
+    }
+
+    pub fn balance(&self, uuid: u128) -> i64 {
+        self.accounts
+            .accounts
+            .get(&uuid_string(uuid))
+            .map_or(0, |a| a.balance)
+    }
+
+    /// The account of a player who is on: opened with the starting balance
+    /// the first time (logged), its name kept up to date.
+    pub fn seen(&mut self, uuid: u128, name: &str) {
+        let key = uuid_string(uuid);
+        match self.accounts.accounts.get_mut(&key) {
+            Some(a) if a.name == name => {}
+            Some(a) => {
+                a.name = name.to_owned();
+                self.dirty = true;
+            }
+            None => {
+                let start = self.config.starting_balance.clamp(0, MAX_AMOUNT);
+                let entry = self.entry("open", None, Some(uuid), start, "");
+                if self.audit.append(&entry).is_ok() {
+                    self.accounts.accounts.insert(
+                        key,
+                        Account {
+                            name: name.to_owned(),
+                            balance: start,
+                        },
+                    );
+                    self.dirty = true;
+                }
+            }
+        }
+    }
+
+    /// An account by the name last seen, any case.
+    pub fn find(&self, name: &str) -> Option<(u128, &Account)> {
+        self.accounts
+            .accounts
+            .iter()
+            .find(|(_, a)| a.name.eq_ignore_ascii_case(name))
+            .and_then(|(k, a)| Some((super::smp_store::parse_uuid(k)?, a)))
+    }
+
+    /// `1,250 coins`.
+    pub fn money(&self, amount: i64) -> String {
+        let digits = amount.unsigned_abs().to_string();
+        let mut out = String::new();
+        for (i, c) in digits.chars().enumerate() {
+            if i > 0 && (digits.len() - i).is_multiple_of(3) {
+                out.push(',');
+            }
+            out.push(c);
+        }
+        let sign = if amount < 0 { "-" } else { "" };
+        format!("{sign}{out} {}", self.config.currency)
+    }
+
+    fn entry(
+        &self,
+        kind: &str,
+        from: Option<u128>,
+        to: Option<u128>,
+        amount: i64,
+        by: &str,
+    ) -> serde_json::Value {
+        let after = |u: Option<u128>| u.map(|u| self.balance(u));
+        let mut e = serde_json::json!({
+            "time": self.now,
+            "kind": kind,
+            "amount": amount,
+        });
+        if let Some(f) = from {
+            e["from"] = uuid_string(f).into();
+            e["from_before"] = after(Some(f)).into();
+        }
+        if let Some(t) = to {
+            e["to"] = uuid_string(t).into();
+            e["to_before"] = after(Some(t)).into();
+        }
+        if !by.is_empty() {
+            e["by"] = by.into();
+        }
+        e
+    }
+
+    /// Moves `amount` from one account to another, logged as `kind`. Both
+    /// must exist; `from` must hold it.
+    pub fn transfer(
+        &mut self,
+        kind: &str,
+        from: u128,
+        to: u128,
+        amount: i64,
+    ) -> Result<(), String> {
+        if amount <= 0 || amount > MAX_AMOUNT {
+            return Err("The amount must be a positive whole number.".into());
+        }
+        if from == to {
+            return Err("You can't pay yourself.".into());
+        }
+        let (Some(f), Some(t)) = (
+            self.accounts.accounts.get(&uuid_string(from)),
+            self.accounts.accounts.get(&uuid_string(to)),
+        ) else {
+            return Err("No such account.".into());
+        };
+        if f.balance < amount {
+            return Err(format!("You only have {}.", self.money(f.balance)));
+        }
+        let Some(to_after) = t
+            .balance
+            .checked_add(amount)
+            .filter(|b| *b <= MAX_AMOUNT * 1000)
+        else {
+            return Err("That account can't hold more.".into());
+        };
+        let entry = self.entry(kind, Some(from), Some(to), amount, "");
+        self.audit.append(&entry)?;
+        self.accounts
+            .accounts
+            .get_mut(&uuid_string(from))
+            .expect("checked")
+            .balance -= amount;
+        self.accounts
+            .accounts
+            .get_mut(&uuid_string(to))
+            .expect("checked")
+            .balance = to_after;
+        self.dirty = true;
+        Ok(())
+    }
+
+    /// Adds (or with a negative `delta`, takes) money from the server: the
+    /// market, games, operators. The balance never goes below zero.
+    pub fn adjust(&mut self, kind: &str, uuid: u128, delta: i64, by: &str) -> Result<i64, String> {
+        let key = uuid_string(uuid);
+        let Some(a) = self.accounts.accounts.get(&key) else {
+            return Err("No such account.".into());
+        };
+        let after = a.balance.saturating_add(delta);
+        if after < 0 {
+            return Err(format!("Only {} there.", self.money(a.balance)));
+        }
+        if after > MAX_AMOUNT * 1000 {
+            return Err("That account can't hold more.".into());
+        }
+        let (from, to) = if delta < 0 {
+            (Some(uuid), None)
+        } else {
+            (None, Some(uuid))
+        };
+        let entry = self.entry(kind, from, to, delta.abs(), by);
+        self.audit.append(&entry)?;
+        self.accounts
+            .accounts
+            .get_mut(&key)
+            .expect("checked")
+            .balance = after;
+        self.dirty = true;
+        Ok(after)
+    }
+
+    /// Appends a line of another kind to the audit log (a trade's items),
+    /// with the time; the change it records waits for it.
+    pub fn record(&mut self, mut entry: serde_json::Value) -> Result<(), String> {
+        entry["time"] = self.now.into();
+        self.audit.append(&entry)
+    }
+
+    /// The accounts, richest first (then by name).
+    pub fn top(&self) -> Vec<(&str, i64)> {
+        let mut all: Vec<_> = self
+            .accounts
+            .accounts
+            .values()
+            .map(|a| (a.name.as_str(), a.balance))
+            .collect();
+        all.sort_by(|a, b| b.1.cmp(&a.1).then_with(|| a.0.cmp(b.0)));
+        all
+    }
+
+    /// Runs `/balance`, `/bal`, `/pay`, `/baltop` or `/eco`; None for another
+    /// command.
+    pub fn command(&mut self, me: &Player, line: &str) -> Option<Vec<Out>> {
+        let words: Vec<&str> = line.split_whitespace().collect();
+        let (&name, args) = words.split_first()?;
+        Some(match name {
+            "balance" | "bal" => self.balance_command(me, args),
+            "pay" => self.pay(me, args),
+            "baltop" => self.baltop(args),
+            "eco" => self.eco(me, args),
+            _ => return None,
+        })
+    }
+
+    fn balance_command(&mut self, me: &Player, args: &[&str]) -> Vec<Out> {
+        match args {
+            [] => vec![Out::Reply(format!(
+                "Balance: {}",
+                self.money(self.balance(me.uuid))
+            ))],
+            [who] => match self.find(who) {
+                Some((_, a)) => vec![Out::Reply(format!("{}: {}", a.name, self.money(a.balance)))],
+                None => vec![Out::Error(format!("No player named {who} has an account."))],
+            },
+            _ => vec![Out::Error("Usage: /balance [player]".into())],
+        }
+    }
+
+    fn pay(&mut self, me: &Player, args: &[&str]) -> Vec<Out> {
+        let [who, amount] = args else {
+            return vec![Out::Error("Usage: /pay <player> <amount>".into())];
+        };
+        let Some(amount) = parse_amount(amount) else {
+            return vec![Out::Error(
+                "The amount must be a positive whole number.".into(),
+            )];
+        };
+        let Some((to, account)) = self.find(who) else {
+            return vec![Out::Error(format!("No player named {who} has an account."))];
+        };
+        let to_name = account.name.clone();
+        match self.transfer("pay", me.uuid, to, amount) {
+            Ok(()) => vec![
+                Out::Reply(format!(
+                    "You paid {} to {to_name}. Balance: {}",
+                    self.money(amount),
+                    self.money(self.balance(me.uuid))
+                )),
+                Out::Tell(to, format!("{} paid you {}.", me.name, self.money(amount))),
+            ],
+            Err(e) => vec![Out::Error(e)],
+        }
+    }
+
+    fn baltop(&mut self, args: &[&str]) -> Vec<Out> {
+        let page = match args {
+            [] => 1,
+            [p] => match p.parse::<usize>() {
+                Ok(p) if p >= 1 => p,
+                _ => return vec![Out::Error("Usage: /baltop [page]".into())],
+            },
+            _ => return vec![Out::Error("Usage: /baltop [page]".into())],
+        };
+        let top = self.top();
+        let pages = top.len().div_ceil(PAGE).max(1);
+        let mut out = vec![Out::Reply(format!("Richest players ({page}/{pages}):"))];
+        for (i, (name, balance)) in top.iter().enumerate().skip((page - 1) * PAGE).take(PAGE) {
+            out.push(Out::Reply(format!(
+                "{}. {name}: {}",
+                i + 1,
+                self.money(*balance)
+            )));
+        }
+        out
+    }
+
+    fn eco(&mut self, me: &Player, args: &[&str]) -> Vec<Out> {
+        if me.level < 3 {
+            return vec![Out::Error("Only operators of level 3 may use /eco.".into())];
+        }
+        let [verb, who, amount] = args else {
+            return vec![Out::Error(
+                "Usage: /eco give|take|set <player> <amount>".into(),
+            )];
+        };
+        let amount = match amount.parse::<i64>() {
+            Ok(a) if (0..=MAX_AMOUNT).contains(&a) => a,
+            _ => {
+                return vec![Out::Error(
+                    "The amount must be a whole number from 0.".into(),
+                )];
+            }
+        };
+        let Some((uuid, account)) = self.find(who) else {
+            return vec![Out::Error(format!("No player named {who} has an account."))];
+        };
+        let name = account.name.clone();
+        let delta = match *verb {
+            "give" => amount,
+            "take" => -amount,
+            "set" => amount - account.balance,
+            _ => {
+                return vec![Out::Error(
+                    "Usage: /eco give|take|set <player> <amount>".into(),
+                )];
+            }
+        };
+        let by = uuid_string(me.uuid);
+        match self.adjust(&format!("eco_{verb}"), uuid, delta, &by) {
+            Ok(after) => vec![Out::Reply(format!("{name} now has {}.", self.money(after)))],
+            Err(e) => vec![Out::Error(e)],
+        }
+    }
+}
+
+/// A positive whole amount, `1250` or `1,250`.
+pub fn parse_amount(s: &str) -> Option<i64> {
+    let digits: String = s.chars().filter(|c| *c != ',').collect();
+    if digits.is_empty() || !digits.chars().all(|c| c.is_ascii_digit()) {
+        return None;
+    }
+    digits
+        .parse::<i64>()
+        .ok()
+        .filter(|a| (1..=MAX_AMOUNT).contains(a))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+
+    const ALEX: u128 = 1;
+    const STEVE: u128 = 2;
+
+    fn player(uuid: u128, name: &str, level: u8) -> Player {
+        Player {
+            uuid,
+            name: name.into(),
+            level,
+        }
+    }
+
+    fn economy(name: &str) -> (Economy, PathBuf) {
+        let dir = std::env::temp_dir().join(format!("smp-economy-{name}-{}", std::process::id()));
+        let _ = fs::remove_dir_all(&dir);
+        let config = Config {
+            starting_balance: 100,
+            ..Config::default()
+        };
+        let mut e = Economy::open(&dir, config).unwrap();
+        e.seen(ALEX, "Alex");
+        e.seen(STEVE, "Steve");
+        (e, dir)
+    }
+
+    fn log_lines(dir: &std::path::Path) -> Vec<serde_json::Value> {
+        fs::read_to_string(dir.join("audit.log"))
+            .unwrap()
+            .lines()
+            .map(|l| serde_json::from_str(l).unwrap())
+            .collect()
+    }
+
+    #[test]
+    fn pay_moves_money_and_tells_both() {
+        let (mut e, dir) = economy("pay");
+        let out = e.command(&player(ALEX, "Alex", 0), "pay steve 30").unwrap();
+        assert_eq!(
+            out,
+            [
+                Out::Reply("You paid 30 coins to Steve. Balance: 70 coins".into()),
+                Out::Tell(STEVE, "Alex paid you 30 coins.".into()),
+            ]
+        );
+        assert_eq!((e.balance(ALEX), e.balance(STEVE)), (70, 130));
+        let log = log_lines(&dir);
+        assert_eq!(log.len(), 3, "two accounts opened, one payment");
+        assert_eq!(log[2]["kind"], "pay");
+        assert_eq!(log[2]["from_before"], 100);
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn pay_refuses_what_it_must() {
+        let (mut e, dir) = economy("refuse");
+        let alex = player(ALEX, "Alex", 0);
+        for (line, error) in [
+            ("pay Steve 101", "You only have 100 coins."),
+            ("pay Steve 0", "The amount must be a positive whole number."),
+            (
+                "pay Steve -5",
+                "The amount must be a positive whole number.",
+            ),
+            (
+                "pay Steve 1.5",
+                "The amount must be a positive whole number.",
+            ),
+            ("pay Alex 5", "You can't pay yourself."),
+            (
+                "pay Herobrine 5",
+                "No player named Herobrine has an account.",
+            ),
+            ("pay Steve", "Usage: /pay <player> <amount>"),
+        ] {
+            assert_eq!(
+                e.command(&alex, line).unwrap(),
+                [Out::Error(error.into())],
+                "{line}"
+            );
+        }
+        assert_eq!((e.balance(ALEX), e.balance(STEVE)), (100, 100));
+        assert_eq!(
+            log_lines(&dir).len(),
+            2,
+            "nothing logged but the two accounts"
+        );
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn balances_survive_a_restart_and_a_damaged_file_stops_the_economy() {
+        let (mut e, dir) = economy("restart");
+        e.command(&player(ALEX, "Alex", 0), "pay Steve 1,000")
+            .unwrap();
+        e.command(&player(ALEX, "Alex", 0), "pay Steve 25").unwrap();
+        e.save().unwrap();
+        let again = Economy::open(&dir, Config::default()).unwrap();
+        assert_eq!((again.balance(ALEX), again.balance(STEVE)), (75, 125));
+        fs::write(dir.join("economy.json"), "{ half").unwrap();
+        assert!(Economy::open(&dir, Config::default()).is_err());
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn eco_is_for_level_3_and_never_goes_below_zero() {
+        let (mut e, dir) = economy("eco");
+        let alex = player(ALEX, "Alex", 2);
+        assert_eq!(
+            e.command(&alex, "eco give Steve 5").unwrap(),
+            [Out::Error("Only operators of level 3 may use /eco.".into())]
+        );
+        let op = player(ALEX, "Alex", 3);
+        assert_eq!(
+            e.command(&op, "eco give Steve 5").unwrap(),
+            [Out::Reply("Steve now has 105 coins.".into())]
+        );
+        assert_eq!(
+            e.command(&op, "eco take Steve 200").unwrap(),
+            [Out::Error("Only 105 coins there.".into())]
+        );
+        assert_eq!(
+            e.command(&op, "eco set Steve 1234567").unwrap(),
+            [Out::Reply("Steve now has 1,234,567 coins.".into())]
+        );
+        let log = log_lines(&dir);
+        assert_eq!(log.last().unwrap()["kind"], "eco_set");
+        assert_eq!(log.last().unwrap()["by"], uuid_string(ALEX));
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn baltop_pages_the_richest_first() {
+        let (mut e, dir) = economy("baltop");
+        for i in 0..12u128 {
+            e.seen(100 + i, &format!("P{i:02}"));
+        }
+        e.command(&player(ALEX, "Alex", 0), "pay Steve 50").unwrap();
+        let first = e.command(&player(ALEX, "Alex", 0), "baltop").unwrap();
+        assert_eq!(first[0], Out::Reply("Richest players (1/2):".into()));
+        assert_eq!(first[1], Out::Reply("1. Steve: 150 coins".into()));
+        assert_eq!(first.len(), 11);
+        let last = e.command(&player(ALEX, "Alex", 0), "baltop 2").unwrap();
+        assert_eq!(
+            last.last().unwrap(),
+            &Out::Reply("14. Alex: 50 coins".into())
+        );
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn a_name_change_keeps_the_account() {
+        let (mut e, dir) = economy("rename");
+        e.seen(ALEX, "Alexandra");
+        assert_eq!(e.balance(ALEX), 100);
+        assert!(e.find("alexandra").is_some() && e.find("Alex").is_none());
+        assert_eq!(log_lines(&dir).len(), 2);
+        fs::remove_dir_all(dir).unwrap();
+    }
+}

native/smp/mixins/smp/smp_games.rs

@@ -0,0 +1,465 @@
+// Games of chance with the in-game currency only (`/coinflip`): a player
+// stakes an amount, another matches it, a fair coin decides, the winner
+// takes both stakes. Each stake is held in `economy.json` from the moment it
+// is offered (`Economy::hold`) until the coin falls or the offer ends, so a
+// crash or a restart gives it back and never loses or doubles it. Off by
+// default (`gambling.enabled`); limits, a cooldown and the audit log on every
+// step. Nothing here is bought with real money or paid out of the game
+// (Mojang's usage guidelines). No game types; the coin is the glue's, never
+// the world's random. Added to the game as `game::smp_games`; also a module
+// of this crate, for its tests.
+
+use super::smp_economy::{Economy, Out, Player, parse_amount};
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+/// `config.json`'s `gambling` section.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Config {
+    /// Off until the owner turns it on.
+    pub enabled: bool,
+    pub min_bet: i64,
+    pub max_bet: i64,
+    /// Between two coinflips of one player (offered or accepted).
+    pub cooldown_seconds: i64,
+    /// How long an offer waits before its stake goes back.
+    pub offer_seconds: i64,
+    /// What the server keeps of the pot, in percent (0: the winner takes all).
+    pub fee_percent: i64,
+    /// The lottery: a ticket's price, the tickets one player may hold in a
+    /// draw, and the time from a round's first ticket to its draw.
+    pub ticket_price: i64,
+    pub max_tickets: i64,
+    pub lottery_seconds: i64,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            min_bet: 10,
+            max_bet: 1000,
+            cooldown_seconds: 30,
+            offer_seconds: 60,
+            fee_percent: 0,
+            ticket_price: 10,
+            max_tickets: 100,
+            lottery_seconds: 3600,
+        }
+    }
+}
+
+/// An offer waiting for a taker: its stake is held.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Offer {
+    pub from: u128,
+    pub from_name: String,
+    /// Only this player may take it; anyone when None.
+    pub to: Option<u128>,
+    pub amount: i64,
+    pub at: i64,
+}
+
+#[derive(Default)]
+pub struct Games {
+    pub config: Config,
+    pub offers: Vec<Offer>,
+    /// When each player last played, for the cooldown.
+    last: HashMap<u128, i64>,
+}
+
+const USAGE: &str = "Usage: /coinflip <amount> [player], /coinflip accept <player>, /coinflip cancel, /coinflip list";
+
+impl Games {
+    pub fn new(config: Config) -> Self {
+        Self {
+            config,
+            ..Default::default()
+        }
+    }
+
+    /// The milliseconds `uuid` still waits before playing again.
+    fn cooling(&self, uuid: u128, now: i64) -> i64 {
+        self.last
+            .get(&uuid)
+            .map_or(0, |t| t + self.config.cooldown_seconds * 1000 - now)
+            .max(0)
+    }
+
+    /// Offers nobody took in time: their stakes go back.
+    pub fn expire(&mut self, economy: &mut Economy, now: i64) -> Vec<Out> {
+        let limit = self.config.offer_seconds * 1000;
+        let (old, keep): (Vec<Offer>, Vec<Offer>) =
+            self.offers.drain(..).partition(|o| now - o.at >= limit);
+        self.offers = keep;
+        let mut out = Vec::new();
+        for o in old {
+            // A stake the log refuses to release stays held: given back
+            // when the economy next opens.
+            if economy
+                .release("coinflip_expired", o.from, o.amount)
+                .is_ok()
+            {
+                out.push(Out::Tell(
+                    o.from,
+                    format!(
+                        "Nobody took your coinflip: {} back.",
+                        economy.money(o.amount)
+                    ),
+                ));
+            }
+        }
+        out
+    }
+
+    /// The player left: their offer ends and its stake goes back.
+    pub fn left(&mut self, economy: &mut Economy, uuid: u128) {
+        if let Some(i) = self.offers.iter().position(|o| o.from == uuid) {
+            let o = self.offers.remove(i);
+            // Refused by the log: still held, given back at the next start.
+            let _ = economy.release("coinflip_cancel", o.from, o.amount);
+        }
+    }
+
+    /// `/coinflip ...`; None for another command. `online` finds a player who
+    /// is on by name (uuid, name); `heads` flips the coin.
+    pub fn command(
+        &mut self,
+        economy: &mut Economy,
+        me: &Player,
+        online: &dyn Fn(&str) -> Option<(u128, String)>,
+        now: i64,
+        heads: &mut dyn FnMut() -> bool,
+        line: &str,
+    ) -> Option<Vec<Out>> {
+        let words: Vec<&str> = line.split_whitespace().collect();
+        if words.first() != Some(&"coinflip") {
+            return None;
+        }
+        let err = |s: String| Some(vec![Out::Error(s)]);
+        if !self.config.enabled {
+            return err("Games of chance are off on this server.".into());
+        }
+        let mut out = self.expire(economy, now);
+        let result = match words[1..] {
+            ["list"] => {
+                let open: Vec<String> = self
+                    .offers
+                    .iter()
+                    .filter(|o| o.to.is_none_or(|t| t == me.uuid))
+                    .map(|o| format!("{}: {}", o.from_name, economy.money(o.amount)))
+                    .collect();
+                if open.is_empty() {
+                    vec![Out::Reply("No coinflip is waiting.".into())]
+                } else {
+                    vec![Out::Reply(format!(
+                        "Coinflips waiting: {}",
+                        open.join(", ")
+                    ))]
+                }
+            }
+            ["cancel"] => match self.offers.iter().position(|o| o.from == me.uuid) {
+                None => vec![Out::Error("You have no coinflip waiting.".into())],
+                Some(i) => {
+                    let o = self.offers.remove(i);
+                    match economy.release("coinflip_cancel", o.from, o.amount) {
+                        Ok(()) => vec![Out::Reply(format!(
+                            "Coinflip cancelled: {} back.",
+                            economy.money(o.amount)
+                        ))],
+                        Err(e) => {
+                            self.offers.insert(i, o);
+                            vec![Out::Error(e)]
+                        }
+                    }
+                }
+            },
+            ["accept", name] => self.accept(economy, me, name, now, heads),
+            [amount] | [amount, _] => {
+                let to = match words.get(2) {
+                    None => None,
+                    Some(name) => match online(name) {
+                        Some((uuid, _)) if uuid == me.uuid => {
+                            return err("You can't flip against yourself.".into());
+                        }
+                        Some(found) => Some(found),
+                        None => return err(format!("{name} is not here.")),
+                    },
+                };
+                match parse_amount(amount) {
+                    None => vec![Out::Error(USAGE.into())],
+                    Some(a) => self.offer(economy, me, to, a, now),
+                }
+            }
+            _ => vec![Out::Error(USAGE.into())],
+        };
+        out.extend(result);
+        Some(out)
+    }
+
+    fn offer(
+        &mut self,
+        economy: &mut Economy,
+        me: &Player,
+        to: Option<(u128, String)>,
+        amount: i64,
+        now: i64,
+    ) -> Vec<Out> {
+        let c = &self.config;
+        if !(c.min_bet..=c.max_bet).contains(&amount) {
+            return vec![Out::Error(format!(
+                "A coinflip is {} to {}.",
+                economy.money(c.min_bet),
+                economy.money(c.max_bet)
+            ))];
+        }
+        if self.offers.iter().any(|o| o.from == me.uuid) {
+            return vec![Out::Error(
+                "You already have a coinflip waiting (/coinflip cancel).".into(),
+            )];
+        }
+        let wait = self.cooling(me.uuid, now);
+        if wait > 0 {
+            return vec![Out::Error(format!(
+                "Wait {} s before your next coinflip.",
+                (wait + 999) / 1000
+            ))];
+        }
+        if let Err(e) = economy.hold("coinflip_stake", me.uuid, amount) {
+            return vec![Out::Error(e)];
+        }
+        self.offers.push(Offer {
+            from: me.uuid,
+            from_name: me.name.clone(),
+            to: to.as_ref().map(|(u, _)| *u),
+            amount,
+            at: now,
+        });
+        let money = economy.money(amount);
+        let secs = self.config.offer_seconds;
+        match to {
+            Some((uuid, name)) => vec![
+                Out::Reply(format!("Coinflip of {money} offered to {name} ({secs} s).")),
+                Out::Tell(
+                    uuid,
+                    format!(
+                        "{} offers you a coinflip of {money}: /coinflip accept {}",
+                        me.name, me.name
+                    ),
+                ),
+            ],
+            None => vec![Out::Reply(format!(
+                "Coinflip of {money} offered ({secs} s): /coinflip accept {}",
+                me.name
+            ))],
+        }
+    }
+
+    fn accept(
+        &mut self,
+        economy: &mut Economy,
+        me: &Player,
+        name: &str,
+        now: i64,
+        heads: &mut dyn FnMut() -> bool,
+    ) -> Vec<Out> {
+        let Some(i) = self.offers.iter().position(|o| {
+            o.from_name.eq_ignore_ascii_case(name) && o.to.is_none_or(|t| t == me.uuid)
+        }) else {
+            return vec![Out::Error(format!("{name} has no coinflip for you."))];
+        };
+        if self.offers[i].from == me.uuid {
+            return vec![Out::Error("You can't flip against yourself.".into())];
+        }
+        let wait = self.cooling(me.uuid, now);
+        if wait > 0 {
+            return vec![Out::Error(format!(
+                "Wait {} s before your next coinflip.",
+                (wait + 999) / 1000
+            ))];
+        }
+        let amount = self.offers[i].amount;
+        if let Err(e) = economy.hold("coinflip_stake", me.uuid, amount) {
+            return vec![Out::Error(e)];
+        }
+        let o = self.offers.remove(i);
+        let pot = amount * 2;
+        let prize = pot - pot * self.config.fee_percent.clamp(0, 100) / 100;
+        let (winner, loser, winner_name, loser_name) = if heads() {
+            (o.from, me.uuid, o.from_name.as_str(), me.name.as_str())
+        } else {
+            (me.uuid, o.from, me.name.as_str(), o.from_name.as_str())
+        };
+        let stakes = [(o.from, amount), (me.uuid, amount)];
+        if let Err(e) = economy.award("coinflip_win", &stakes, winner, prize) {
+            // Not decided: both stakes go back (or, failing that, at the next start).
+            for (u, a) in stakes {
+                let _ = economy.release("coinflip_cancel", u, a);
+            }
+            return vec![Out::Error(e)];
+        }
+        self.last.insert(o.from, now);
+        self.last.insert(me.uuid, now);
+        let won = economy.money(prize);
+        vec![
+            Out::Tell(
+                winner,
+                format!("Coinflip against {loser_name}: you won {won}!"),
+            ),
+            Out::Tell(
+                loser,
+                format!(
+                    "Coinflip against {winner_name}: you lost {}.",
+                    economy.money(amount)
+                ),
+            ),
+        ]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const A: u128 = 1;
+    const B: u128 = 2;
+
+    fn setup(name: &str) -> (Economy, Games, std::path::PathBuf) {
+        let dir = std::env::temp_dir().join(format!("smp-games-{name}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let mut e = Economy::open(&dir, Default::default()).unwrap();
+        e.seen(A, "Alex");
+        e.seen(B, "Steve");
+        e.adjust("eco_give", A, 500, "test").unwrap();
+        e.adjust("eco_give", B, 500, "test").unwrap();
+        let g = Games::new(Config {
+            enabled: true,
+            ..Default::default()
+        });
+        (e, g, dir)
+    }
+    fn player(uuid: u128) -> Player {
+        Player {
+            uuid,
+            name: if uuid == A { "Alex" } else { "Steve" }.into(),
+            level: 0,
+        }
+    }
+    fn online(name: &str) -> Option<(u128, String)> {
+        match name.to_ascii_lowercase().as_str() {
+            "alex" => Some((A, "Alex".into())),
+            "steve" => Some((B, "Steve".into())),
+            _ => None,
+        }
+    }
+    fn run(
+        e: &mut Economy,
+        g: &mut Games,
+        who: u128,
+        now: i64,
+        heads: bool,
+        line: &str,
+    ) -> Vec<Out> {
+        g.command(e, &player(who), &online, now, &mut || heads, line)
+            .unwrap()
+    }
+    fn total(e: &Economy) -> i64 {
+        e.balance(A) + e.balance(B) + e.held(A) + e.held(B)
+    }
+
+    #[test]
+    fn the_stake_is_held_then_the_winner_takes_both() {
+        let (mut e, mut g, dir) = setup("win");
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        assert_eq!((e.balance(A), e.held(A)), (400, 100));
+        let out = run(&mut e, &mut g, B, 1000, true, "coinflip accept alex");
+        assert!(
+            matches!(&out[0], Out::Tell(A, s) if s.contains("you won 200 coins")),
+            "{out:?}"
+        );
+        assert_eq!(
+            (e.balance(A), e.balance(B), e.held(A), e.held(B)),
+            (600, 400, 0, 0)
+        );
+        // Tails: the taker wins.
+        run(&mut e, &mut g, A, 100_000, false, "coinflip 50 steve");
+        run(&mut e, &mut g, B, 101_000, false, "coinflip accept Alex");
+        assert_eq!((e.balance(A), e.balance(B)), (550, 450));
+        assert_eq!(total(&e), 1000, "nothing made or lost");
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn limits_cooldown_and_refusals() {
+        let (mut e, mut g, dir) = setup("limits");
+        for line in [
+            "coinflip 5",
+            "coinflip 1001",
+            "coinflip 100 alex",
+            "coinflip 100 nobody",
+            "coinflip x",
+        ] {
+            assert!(
+                matches!(&run(&mut e, &mut g, A, 0, true, line)[0], Out::Error(_)),
+                "{line}"
+            );
+        }
+        assert_eq!(total(&e), 1000);
+        assert_eq!(e.held(A), 0);
+        // More than the balance.
+        e.adjust("eco_take", B, -480, "test").unwrap();
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        assert!(matches!(
+            &run(&mut e, &mut g, B, 0, true, "coinflip accept alex")[0],
+            Out::Error(_)
+        ));
+        assert_eq!(e.held(A), 100, "the offer still waits");
+        // Only the named player may take a named offer.
+        run(&mut e, &mut g, A, 0, true, "coinflip cancel");
+        e.adjust("eco_give", B, 480, "test").unwrap();
+        // Cooldown after a game.
+        run(&mut e, &mut g, A, 0, true, "coinflip 10");
+        run(&mut e, &mut g, B, 0, true, "coinflip accept alex");
+        assert!(
+            matches!(&run(&mut e, &mut g, A, 10_000, true, "coinflip 10")[0], Out::Error(s) if s.contains("Wait 20 s"))
+        );
+        assert!(matches!(
+            &run(&mut e, &mut g, A, 30_000, true, "coinflip 10")[0],
+            Out::Reply(_)
+        ));
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn off_by_default() {
+        let (mut e, _, dir) = setup("off");
+        let mut g = Games::default();
+        assert!(
+            matches!(&run(&mut e, &mut g, A, 0, true, "coinflip 100")[0], Out::Error(s) if s.contains("off"))
+        );
+        assert_eq!(e.held(A), 0);
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn every_way_out_gives_the_stake_back() {
+        let (mut e, mut g, dir) = setup("out");
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        run(&mut e, &mut g, A, 0, true, "coinflip cancel");
+        assert_eq!((e.balance(A), e.held(A)), (500, 0));
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        let out = g.expire(&mut e, 60_000);
+        assert!(matches!(&out[0], Out::Tell(A, _)));
+        assert_eq!((e.balance(A), e.held(A)), (500, 0));
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        g.left(&mut e, A);
+        assert_eq!((e.balance(A), e.held(A)), (500, 0));
+        // A crash with a stake held: saved, then opened again, it goes back.
+        run(&mut e, &mut g, A, 0, true, "coinflip 100");
+        e.save().unwrap();
+        let again = Economy::open(&dir, Default::default()).unwrap();
+        assert_eq!((again.balance(A), again.held(A)), (500, 0));
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+}

native/smp/mixins/smp/smp_lottery.rs

@@ -0,0 +1,258 @@
+// The lottery (`/lottery`): players buy tickets with the in-game currency;
+// once `lottery_seconds` have passed since a round's first ticket, one ticket
+// is drawn at random and its owner takes the pot. The tickets' money is held
+// in `economy.json` (`Economy::hold`) until the draw, so a crash or a restart
+// gives every ticket back and never loses or doubles the pot. A round with a
+// single player is given back too: there is nobody to win from. Part of
+// `gambling` (off by default); nothing here is bought with real money or
+// paid out of the game. No game types; the draw is the glue's random, never
+// the world's. Added to the game as `game::smp_lottery`; also a module of
+// this crate, for its tests.
+
+use super::smp_economy::{Economy, Out, Player, parse_amount};
+use super::smp_games::Config;
+
+/// The round being sold.
+#[derive(Default)]
+pub struct Lottery {
+    /// Tickets by player, in the order they first bought: (uuid, name, tickets).
+    pub tickets: Vec<(u128, String, i64)>,
+    /// When the round draws (ms); None until its first ticket.
+    pub draw_at: Option<i64>,
+}
+
+impl Lottery {
+    fn pot(&self, price: i64) -> i64 {
+        self.tickets.iter().map(|t| t.2).sum::<i64>() * price
+    }
+
+    /// `/lottery` and `/lottery buy <tickets>`; None for another command.
+    pub fn command(
+        &mut self,
+        config: &Config,
+        economy: &mut Economy,
+        me: &Player,
+        now: i64,
+        line: &str,
+    ) -> Option<Vec<Out>> {
+        let words: Vec<&str> = line.split_whitespace().collect();
+        if words.first() != Some(&"lottery") {
+            return None;
+        }
+        if !config.enabled {
+            return Some(vec![Out::Error(
+                "Games of chance are off on this server.".into(),
+            )]);
+        }
+        let price = config.ticket_price.max(1);
+        let mine = self
+            .tickets
+            .iter()
+            .find(|t| t.0 == me.uuid)
+            .map_or(0, |t| t.2);
+        Some(match words[1..] {
+            [] => {
+                let when = match self.draw_at {
+                    Some(t) => format!("draws in {} s", ((t - now).max(0) + 999) / 1000),
+                    None => "draws once tickets are bought".into(),
+                };
+                vec![Out::Reply(format!(
+                    "Lottery: pot {}, {} ticket(s) of yours, {when}. A ticket costs {}: /lottery buy <tickets>",
+                    economy.money(self.pot(price)),
+                    mine,
+                    economy.money(price)
+                ))]
+            }
+            ["buy", n] => match parse_amount(n) {
+                None => vec![Out::Error("Usage: /lottery buy <tickets>".into())],
+                Some(n) if mine + n > config.max_tickets => vec![Out::Error(format!(
+                    "{} tickets a draw at most; you have {mine}.",
+                    config.max_tickets
+                ))],
+                Some(n) => match economy.hold("lottery_ticket", me.uuid, n * price) {
+                    Err(e) => vec![Out::Error(e)],
+                    Ok(()) => {
+                        match self.tickets.iter_mut().find(|t| t.0 == me.uuid) {
+                            Some(t) => t.2 += n,
+                            None => self.tickets.push((me.uuid, me.name.clone(), n)),
+                        }
+                        let draw = *self
+                            .draw_at
+                            .get_or_insert(now + config.lottery_seconds * 1000);
+                        vec![Out::Reply(format!(
+                            "You bought {n} ticket(s) for {}; the pot is {}, drawn in {} s.",
+                            economy.money(n * price),
+                            economy.money(self.pot(price)),
+                            ((draw - now).max(0) + 999) / 1000
+                        ))]
+                    }
+                },
+            },
+            _ => vec![Out::Error("Usage: /lottery, /lottery buy <tickets>".into())],
+        })
+    }
+
+    /// Draws the round when its time has come: `pick(n)` is a random number
+    /// below `n`. Nothing before then.
+    pub fn tick(
+        &mut self,
+        config: &Config,
+        economy: &mut Economy,
+        now: i64,
+        pick: &mut dyn FnMut(u64) -> u64,
+    ) -> Vec<Out> {
+        if self.draw_at.is_none_or(|t| now < t) {
+            return Vec::new();
+        }
+        let price = config.ticket_price.max(1);
+        let round = std::mem::take(self);
+        let stakes: Vec<(u128, i64)> = round.tickets.iter().map(|t| (t.0, t.2 * price)).collect();
+        if round.tickets.len() < 2 {
+            // Nobody to win from: the tickets go back.
+            for (uuid, amount) in &stakes {
+                let _ = economy.release("lottery_refund", *uuid, *amount);
+            }
+            return round
+                .tickets
+                .iter()
+                .map(|t| {
+                    Out::Tell(
+                        t.0,
+                        "The lottery had no other player: your tickets were given back.".into(),
+                    )
+                })
+                .collect();
+        }
+        let total: i64 = round.tickets.iter().map(|t| t.2).sum();
+        let mut ticket = pick(total as u64) as i64;
+        let winner = round
+            .tickets
+            .iter()
+            .find(|t| {
+                ticket -= t.2;
+                ticket < 0
+            })
+            .expect("the ticket is below the total");
+        let pot = total * price;
+        let prize = pot - pot * config.fee_percent.clamp(0, 100) / 100;
+        match economy.award("lottery_win", &stakes, winner.0, prize) {
+            Ok(()) => vec![Out::All(format!(
+                "Lottery: {} won {} with {} of {total} tickets!",
+                winner.1,
+                economy.money(prize),
+                winner.2
+            ))],
+            Err(_) => {
+                // Not drawn: the tickets go back (or at the next start).
+                for (uuid, amount) in &stakes {
+                    let _ = economy.release("lottery_refund", *uuid, *amount);
+                }
+                vec![Out::All(
+                    "The lottery couldn't be drawn: every ticket was given back.".into(),
+                )]
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const A: u128 = 1;
+    const B: u128 = 2;
+
+    fn setup(name: &str) -> (Economy, Config, std::path::PathBuf) {
+        let dir = std::env::temp_dir().join(format!("smp-lottery-{name}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let mut e = Economy::open(&dir, Default::default()).unwrap();
+        e.seen(A, "Alex");
+        e.seen(B, "Steve");
+        e.adjust("eco_give", A, 500, "test").unwrap();
+        e.adjust("eco_give", B, 500, "test").unwrap();
+        let c = Config {
+            enabled: true,
+            ..Default::default()
+        };
+        (e, c, dir)
+    }
+    fn player(uuid: u128) -> Player {
+        Player {
+            uuid,
+            name: if uuid == A { "Alex" } else { "Steve" }.into(),
+            level: 0,
+        }
+    }
+
+    #[test]
+    fn tickets_are_held_and_one_is_drawn_for_the_pot() {
+        let (mut e, c, dir) = setup("draw");
+        let mut l = Lottery::default();
+        l.command(&c, &mut e, &player(A), 0, "lottery buy 3")
+            .unwrap();
+        l.command(&c, &mut e, &player(B), 1000, "lottery buy 1")
+            .unwrap();
+        assert_eq!(
+            (e.balance(A), e.held(A), e.balance(B), e.held(B)),
+            (470, 30, 490, 10)
+        );
+        // Not yet: the round draws an hour after its first ticket.
+        assert!(l.tick(&c, &mut e, 3_599_999, &mut |_| 0).is_empty());
+        // Ticket 3 (the fourth) is Steve's.
+        let out = l.tick(&c, &mut e, 3_600_000, &mut |n| {
+            assert_eq!(n, 4);
+            3
+        });
+        assert!(
+            matches!(&out[0], Out::All(s) if s.contains("Steve won 40 coins with 1 of 4")),
+            "{out:?}"
+        );
+        assert_eq!(
+            (e.balance(A), e.balance(B), e.held(A), e.held(B)),
+            (470, 530, 0, 0)
+        );
+        assert!(l.tickets.is_empty() && l.draw_at.is_none(), "a new round");
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn a_round_of_one_player_is_given_back() {
+        let (mut e, c, dir) = setup("alone");
+        let mut l = Lottery::default();
+        l.command(&c, &mut e, &player(A), 0, "lottery buy 5")
+            .unwrap();
+        l.tick(&c, &mut e, 3_600_000, &mut |_| 0);
+        assert_eq!((e.balance(A), e.held(A)), (500, 0));
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn limits_and_off_by_default() {
+        let (mut e, c, dir) = setup("limits");
+        let mut l = Lottery::default();
+        let out = l
+            .command(&c, &mut e, &player(A), 0, "lottery buy 101")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(s) if s.contains("100 tickets")));
+        let out = l
+            .command(&c, &mut e, &player(A), 0, "lottery buy 51")
+            .unwrap();
+        assert!(
+            matches!(&out[0], Out::Error(_)),
+            "510 coins is more than 500"
+        );
+        assert_eq!(e.held(A), 0);
+        let off = Config::default();
+        let out = l
+            .command(&off, &mut e, &player(A), 0, "lottery buy 1")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(s) if s.contains("off")));
+        // A restart gives held tickets back.
+        l.command(&c, &mut e, &player(A), 0, "lottery buy 2")
+            .unwrap();
+        e.save().unwrap();
+        let again = Economy::open(&dir, Default::default()).unwrap();
+        assert_eq!((again.balance(A), again.held(A)), (500, 0));
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+}

native/smp/mixins/smp/smp_market.rs

@@ -0,0 +1,518 @@
+// The server market: the server buys and sells vanilla items at the prices
+// of `config.json`'s `market`, the economy's way to earn without changing
+// survival. `/worth`, `/sell hand|all|<item> [count]`, `/buy <item> [count]`.
+// Only plain items (no damage, no name or enchantment) are traded, and only
+// by players in survival or adventure mode. Items move first, then money,
+// both logged; a sale the log refuses gives the items back. No game types:
+// the glue lends the acting player's items as a `Bag`. Added to the game as
+// `game::smp_market`; also a module of this crate, for its tests.
+
+use super::smp_economy::{Economy, MAX_AMOUNT, Out, Player, parse_amount};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+
+/// What the server pays for one item (`sell`) and asks for one (`buy`); 0
+/// closes that side.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Price {
+    pub buy: i64,
+    pub sell: i64,
+}
+
+/// `config.json`'s `market`.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Config {
+    pub enabled: bool,
+    /// By item id, `minecraft:diamond`.
+    pub items: BTreeMap<String, Price>,
+}
+
+impl Default for Config {
+    /// A small starting list the owner edits: farm and mine produce the
+    /// server buys, a few things it sells, buying always dearer than selling.
+    fn default() -> Self {
+        let list: [(&str, i64, i64); 18] = [
+            ("minecraft:wheat", 0, 1),
+            ("minecraft:carrot", 0, 1),
+            ("minecraft:potato", 0, 1),
+            ("minecraft:sugar_cane", 0, 1),
+            ("minecraft:pumpkin", 0, 3),
+            ("minecraft:melon_slice", 0, 1),
+            ("minecraft:cactus", 0, 1),
+            ("minecraft:oak_log", 4, 1),
+            ("minecraft:coal", 8, 2),
+            ("minecraft:iron_ingot", 30, 8),
+            ("minecraft:gold_ingot", 40, 10),
+            ("minecraft:redstone", 4, 1),
+            ("minecraft:lapis_lazuli", 8, 2),
+            ("minecraft:emerald", 80, 20),
+            ("minecraft:diamond", 400, 100),
+            ("minecraft:bread", 5, 0),
+            ("minecraft:cooked_beef", 6, 0),
+            ("minecraft:torch", 1, 0),
+        ];
+        Self {
+            enabled: true,
+            items: list
+                .iter()
+                .map(|(id, buy, sell)| {
+                    (
+                        (*id).to_owned(),
+                        Price {
+                            buy: *buy,
+                            sell: *sell,
+                        },
+                    )
+                })
+                .collect(),
+        }
+    }
+}
+
+/// The acting player's items, lent by the game for one command.
+pub trait Bag {
+    /// The main hand: item id, count, plain.
+    fn held(&self) -> Option<(String, u32, bool)>;
+    /// Every plain item carried, with how many.
+    fn carried(&self) -> Vec<(String, u32)>;
+    fn count(&mut self, item: &str) -> u32;
+    /// Takes up to `count`; what it took.
+    fn take(&mut self, item: &str, count: u32) -> u32;
+    /// How many more fit.
+    fn room(&mut self, item: &str) -> u32;
+    /// Gives up to `count` where they fit; what it gave.
+    fn give(&mut self, item: &str, count: u32) -> u32;
+}
+
+/// `diamond` or `minecraft:diamond` as `minecraft:diamond`.
+pub fn item_id(name: &str) -> String {
+    let name = name.to_ascii_lowercase();
+    if name.contains(':') {
+        name
+    } else {
+        format!("minecraft:{name}")
+    }
+}
+
+/// `minecraft:iron_ingot` as `iron ingot`.
+pub fn item_name(id: &str) -> String {
+    id.strip_prefix("minecraft:")
+        .unwrap_or(id)
+        .replace('_', " ")
+}
+
+pub struct Market {
+    pub config: Config,
+}
+
+impl Market {
+    /// Runs `/worth`, `/sell` or `/buy`; None for another command. `trades`
+    /// is false for a player in creative or spectator mode.
+    pub fn command(
+        &self,
+        economy: &mut Economy,
+        me: &Player,
+        trades: bool,
+        bag: &mut dyn Bag,
+        line: &str,
+    ) -> Option<Vec<Out>> {
+        let words: Vec<&str> = line.split_whitespace().collect();
+        let (&name, args) = words.split_first()?;
+        if !matches!(name, "worth" | "sell" | "buy") {
+            return None;
+        }
+        if !self.config.enabled {
+            return Some(vec![Out::Error("The market is closed.".into())]);
+        }
+        if name == "worth" {
+            return Some(self.worth(economy, bag, args));
+        }
+        if !trades {
+            return Some(vec![Out::Error(
+                "The market trades only with players in survival or adventure mode.".into(),
+            )]);
+        }
+        Some(match name {
+            "sell" => self.sell(economy, me, bag, args),
+            _ => self.buy(economy, me, bag, args),
+        })
+    }
+
+    fn price(&self, id: &str) -> Price {
+        self.config.items.get(id).copied().unwrap_or_default()
+    }
+
+    fn worth(&self, economy: &Economy, bag: &mut dyn Bag, args: &[&str]) -> Vec<Out> {
+        let id = match args {
+            [] => match bag.held() {
+                Some((id, ..)) => id,
+                None => {
+                    return vec![Out::Error(
+                        "Hold an item, or name one: /worth <item>".into(),
+                    )];
+                }
+            },
+            [item] => item_id(item),
+            _ => return vec![Out::Error("Usage: /worth [item]".into())],
+        };
+        let p = self.price(&id);
+        let name = item_name(&id);
+        let mut parts = Vec::new();
+        if p.sell > 0 {
+            parts.push(format!("the market pays {} each", economy.money(p.sell)));
+        }
+        if p.buy > 0 {
+            parts.push(format!("sells it for {} each", economy.money(p.buy)));
+        }
+        if parts.is_empty() {
+            return vec![Out::Reply(format!("The market doesn't trade {name}."))];
+        }
+        vec![Out::Reply(format!("{name}: {}.", parts.join(", ")))]
+    }
+
+    fn sell(
+        &self,
+        economy: &mut Economy,
+        me: &Player,
+        bag: &mut dyn Bag,
+        args: &[&str],
+    ) -> Vec<Out> {
+        let usage = || vec![Out::Error("Usage: /sell hand|all|<item> [count]".into())];
+        // What to sell: (item, at most how many).
+        let wanted: Vec<(String, u32)> = match args {
+            ["all"] => bag
+                .carried()
+                .into_iter()
+                .filter(|(id, _)| self.price(id).sell > 0)
+                .collect(),
+            ["hand", rest @ ..] => {
+                let Some((id, count, plain)) = bag.held() else {
+                    return vec![Out::Error("Your hand is empty.".into())];
+                };
+                if !plain {
+                    return vec![Out::Error(
+                        "The market only takes plain items (not worn, named or enchanted).".into(),
+                    )];
+                }
+                match rest {
+                    [] => vec![(id, count)],
+                    [n] => match parse_count(n) {
+                        Some(n) => vec![(id, n.min(count))],
+                        None => return usage(),
+                    },
+                    _ => return usage(),
+                }
+            }
+            [item] => vec![(item_id(item), u32::MAX)],
+            [item, n] => match parse_count(n) {
+                Some(n) => vec![(item_id(item), n)],
+                None => return usage(),
+            },
+            _ => return usage(),
+        };
+        if wanted.is_empty() {
+            return vec![Out::Error("You carry nothing the market buys.".into())];
+        }
+        let mut out = Vec::new();
+        let mut total = 0i64;
+        for (id, at_most) in wanted {
+            let price = self.price(&id).sell;
+            let name = item_name(&id);
+            if price <= 0 {
+                out.push(Out::Error(format!("The market doesn't buy {name}.")));
+                continue;
+            }
+            // Never more than the account can be paid for at once.
+            let cap = (MAX_AMOUNT / price).min(u32::MAX as i64) as u32;
+            let have = bag.count(&id).min(at_most).min(cap);
+            if have == 0 {
+                out.push(Out::Error(format!("You have no plain {name}.")));
+                continue;
+            }
+            let taken = bag.take(&id, have);
+            let pay = price * i64::from(taken);
+            let kind = format!("sell {taken} {id}");
+            match economy.adjust(&kind, me.uuid, pay, "") {
+                Ok(_) => {
+                    total += pay;
+                    out.push(Out::Reply(format!(
+                        "Sold {taken} {name} for {}.",
+                        economy.money(pay)
+                    )));
+                }
+                Err(e) => {
+                    let back = bag.give(&id, taken);
+                    out.push(Out::Error(format!(
+                        "The sale failed ({e}); {back} {name} given back."
+                    )));
+                }
+            }
+        }
+        if total > 0 {
+            out.push(Out::Reply(format!(
+                "Balance: {}",
+                economy.money(economy.balance(me.uuid))
+            )));
+        }
+        out
+    }
+
+    fn buy(
+        &self,
+        economy: &mut Economy,
+        me: &Player,
+        bag: &mut dyn Bag,
+        args: &[&str],
+    ) -> Vec<Out> {
+        let (item, count) = match args {
+            [item] => (*item, 1),
+            [item, n] => match parse_count(n) {
+                Some(n) => (*item, n),
+                None => return vec![Out::Error("Usage: /buy <item> [count]".into())],
+            },
+            _ => return vec![Out::Error("Usage: /buy <item> [count]".into())],
+        };
+        let id = item_id(item);
+        let name = item_name(&id);
+        let price = self.price(&id).buy;
+        if price <= 0 {
+            return vec![Out::Error(format!("The market doesn't sell {name}."))];
+        }
+        if count > 64 * 36 {
+            return vec![Out::Error("At most a full inventory at once.".into())];
+        }
+        let cost = price * i64::from(count);
+        if economy.balance(me.uuid) < cost {
+            return vec![Out::Error(format!(
+                "{count} {name} cost {}; you have {}.",
+                economy.money(cost),
+                economy.money(economy.balance(me.uuid))
+            ))];
+        }
+        let room = bag.room(&id);
+        if room < count {
+            return vec![Out::Error(format!(
+                "Only {room} {name} fit in your inventory."
+            ))];
+        }
+        if let Err(e) = economy.adjust(&format!("buy {count} {id}"), me.uuid, -cost, "") {
+            return vec![Out::Error(e)];
+        }
+        let given = bag.give(&id, count);
+        let mut out = vec![Out::Reply(format!(
+            "Bought {given} {name} for {}.",
+            economy.money(cost)
+        ))];
+        if given < count {
+            // Checked above; kept so money never goes for nothing.
+            let refund = price * i64::from(count - given);
+            if economy
+                .adjust(
+                    &format!("refund {} {id}", count - given),
+                    me.uuid,
+                    refund,
+                    "",
+                )
+                .is_ok()
+            {
+                out.push(Out::Reply(format!(
+                    "{} refunded for what didn't fit.",
+                    economy.money(refund)
+                )));
+            }
+        }
+        out.push(Out::Reply(format!(
+            "Balance: {}",
+            economy.money(economy.balance(me.uuid))
+        )));
+        out
+    }
+}
+
+fn parse_count(s: &str) -> Option<u32> {
+    parse_amount(s).and_then(|n| u32::try_from(n).ok())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::smp_economy::Config as EconomyConfig;
+    use super::*;
+    use std::fs;
+
+    /// A pretend inventory: plain stacks by item, one held item, a room cap.
+    struct TestBag {
+        items: BTreeMap<String, u32>,
+        held: Option<(String, u32, bool)>,
+        room: u32,
+    }
+
+    impl Bag for TestBag {
+        fn held(&self) -> Option<(String, u32, bool)> {
+            self.held.clone()
+        }
+        fn carried(&self) -> Vec<(String, u32)> {
+            self.items.iter().map(|(k, v)| (k.clone(), *v)).collect()
+        }
+        fn count(&mut self, item: &str) -> u32 {
+            self.items.get(item).copied().unwrap_or(0)
+        }
+        fn take(&mut self, item: &str, count: u32) -> u32 {
+            let have = self.items.entry(item.into()).or_default();
+            let n = (*have).min(count);
+            *have -= n;
+            n
+        }
+        fn room(&mut self, _item: &str) -> u32 {
+            self.room
+        }
+        fn give(&mut self, item: &str, count: u32) -> u32 {
+            let n = count.min(self.room);
+            self.room -= n;
+            *self.items.entry(item.into()).or_default() += n;
+            n
+        }
+    }
+
+    const ALEX: u128 = 1;
+
+    fn setup(name: &str) -> (Economy, Market, Player, std::path::PathBuf) {
+        let dir = std::env::temp_dir().join(format!("smp-market-{name}-{}", std::process::id()));
+        let _ = fs::remove_dir_all(&dir);
+        let mut e = Economy::open(&dir, EconomyConfig::default()).unwrap();
+        e.seen(ALEX, "Alex");
+        let me = Player {
+            uuid: ALEX,
+            name: "Alex".into(),
+            level: 0,
+        };
+        (
+            e,
+            Market {
+                config: Config::default(),
+            },
+            me,
+            dir,
+        )
+    }
+
+    fn bag(items: &[(&str, u32)], room: u32) -> TestBag {
+        TestBag {
+            items: items.iter().map(|(k, v)| ((*k).into(), *v)).collect(),
+            held: None,
+            room,
+        }
+    }
+
+    #[test]
+    fn selling_takes_the_items_then_pays_and_logs_both() {
+        let (mut e, m, me, dir) = setup("sell");
+        let mut b = bag(
+            &[
+                ("minecraft:diamond", 3),
+                ("minecraft:wheat", 20),
+                ("minecraft:dirt", 64),
+            ],
+            0,
+        );
+        let out = m
+            .command(&mut e, &me, true, &mut b, "sell diamond 2")
+            .unwrap();
+        assert_eq!(out[0], Out::Reply("Sold 2 diamond for 200 coins.".into()));
+        assert_eq!(b.items["minecraft:diamond"], 1);
+        let out = m.command(&mut e, &me, true, &mut b, "sell all").unwrap();
+        assert!(
+            out.contains(&Out::Reply("Sold 1 diamond for 100 coins.".into())),
+            "{out:?}"
+        );
+        assert!(
+            out.contains(&Out::Reply("Sold 20 wheat for 20 coins.".into())),
+            "{out:?}"
+        );
+        assert_eq!(b.items["minecraft:dirt"], 64, "dirt has no price");
+        assert_eq!(e.balance(ALEX), 320);
+        let log = fs::read_to_string(dir.join("audit.log")).unwrap();
+        assert_eq!(log.matches("\"sell ").count(), 3, "{log}");
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn selling_the_hand_takes_only_plain_items() {
+        let (mut e, m, me, dir) = setup("hand");
+        let mut b = bag(&[("minecraft:iron_ingot", 10)], 0);
+        b.held = Some(("minecraft:iron_ingot".into(), 10, true));
+        let out = m.command(&mut e, &me, true, &mut b, "sell hand 4").unwrap();
+        assert_eq!(out[0], Out::Reply("Sold 4 iron ingot for 32 coins.".into()));
+        b.held = Some(("minecraft:diamond_sword".into(), 1, false));
+        let out = m.command(&mut e, &me, true, &mut b, "sell hand").unwrap();
+        assert_eq!(
+            out,
+            [Out::Error(
+                "The market only takes plain items (not worn, named or enchanted).".into()
+            )]
+        );
+        b.held = None;
+        let out = m.command(&mut e, &me, true, &mut b, "sell hand").unwrap();
+        assert_eq!(out, [Out::Error("Your hand is empty.".into())]);
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn buying_checks_money_and_room_before_anything_moves() {
+        let (mut e, m, me, dir) = setup("buy");
+        e.adjust("test", ALEX, 1000, "").unwrap();
+        let mut b = bag(&[], 3);
+        let out = m
+            .command(&mut e, &me, true, &mut b, "buy diamond 3")
+            .unwrap();
+        assert_eq!(
+            out,
+            [Out::Error(
+                "3 diamond cost 1,200 coins; you have 1,000 coins.".into()
+            )]
+        );
+        let out = m.command(&mut e, &me, true, &mut b, "buy torch 4").unwrap();
+        assert_eq!(
+            out,
+            [Out::Error("Only 3 torch fit in your inventory.".into())]
+        );
+        assert_eq!(e.balance(ALEX), 1000);
+        let out = m
+            .command(&mut e, &me, true, &mut b, "buy minecraft:diamond 2")
+            .unwrap();
+        assert_eq!(out[0], Out::Reply("Bought 2 diamond for 800 coins.".into()));
+        assert_eq!((e.balance(ALEX), b.items["minecraft:diamond"]), (200, 2));
+        let out = m.command(&mut e, &me, true, &mut b, "buy wheat").unwrap();
+        assert_eq!(out, [Out::Error("The market doesn't sell wheat.".into())]);
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn creative_players_and_a_closed_market_trade_nothing() {
+        let (mut e, mut m, me, dir) = setup("closed");
+        let mut b = bag(&[("minecraft:diamond", 64)], 64);
+        let out = m.command(&mut e, &me, false, &mut b, "sell all").unwrap();
+        assert_eq!(
+            out,
+            [Out::Error(
+                "The market trades only with players in survival or adventure mode.".into()
+            )]
+        );
+        let worth = m
+            .command(&mut e, &me, false, &mut b, "worth diamond")
+            .unwrap();
+        assert_eq!(
+            worth,
+            [Out::Reply(
+                "diamond: the market pays 100 coins each, sells it for 400 coins each.".into()
+            )]
+        );
+        m.config.enabled = false;
+        let out = m.command(&mut e, &me, true, &mut b, "sell all").unwrap();
+        assert_eq!(out, [Out::Error("The market is closed.".into())]);
+        assert_eq!((e.balance(ALEX), b.items["minecraft:diamond"]), (0, 64));
+        assert!(m.command(&mut e, &me, true, &mut b, "balance").is_none());
+        fs::remove_dir_all(dir).unwrap();
+    }
+}

native/smp/mixins/smp/smp_store.rs

@@ -0,0 +1,190 @@
+// The SMP's files under the world's folder (`world/horizon-smp/`): JSON
+// documents written whole and atomically (a temporary file, flushed, renamed
+// over the old one), and the audit log, one JSON line per transaction,
+// appended before the change it records. Added to the game as
+// `game::smp_store`; also a module of this crate, for its tests.
+
+use std::{
+    fs::{self, File, OpenOptions},
+    io::{self, Write},
+    path::{Path, PathBuf},
+};
+
+/// The folder of the SMP's files in a world's folder.
+pub const DIR: &str = "horizon-smp";
+
+/// Writes `bytes` to `path` so that a crash leaves either the old file or the
+/// new one: a temporary file beside it, flushed to disk, then renamed over it.
+pub fn write_atomic(path: &Path, bytes: &[u8]) -> io::Result<()> {
+    let dir = path.parent().unwrap_or(Path::new("."));
+    fs::create_dir_all(dir)?;
+    let name = path.file_name().and_then(|n| n.to_str()).unwrap_or("file");
+    let temp = dir.join(format!(".{name}.tmp"));
+    {
+        let mut file = File::create(&temp)?;
+        file.write_all(bytes)?;
+        file.sync_all()?;
+    }
+    fs::rename(&temp, path)?;
+    // The rename itself reaches the disk with the folder's entry (Unix).
+    if let Ok(d) = File::open(dir) {
+        let _ = d.sync_all();
+    }
+    Ok(())
+}
+
+/// A JSON document: its default when the file doesn't exist, an error when it
+/// exists but can't be read, so that a damaged file is never replaced by an
+/// empty one.
+pub fn read_json<T: serde::de::DeserializeOwned + Default>(path: &Path) -> Result<T, String> {
+    match fs::read(path) {
+        Ok(bytes) => serde_json::from_slice(&bytes).map_err(|e| format!("{}: {e}", path.display())),
+        Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(T::default()),
+        Err(e) => Err(format!("{}: {e}", path.display())),
+    }
+}
+
+/// Writes a JSON document atomically, pretty-printed.
+pub fn write_json<T: serde::Serialize>(path: &Path, value: &T) -> Result<(), String> {
+    let mut bytes = serde_json::to_vec_pretty(value).map_err(|e| e.to_string())?;
+    bytes.push(b'\n');
+    write_atomic(path, &bytes).map_err(|e| format!("{}: {e}", path.display()))
+}
+
+/// The audit log: `audit.log`, one JSON object a line.
+pub struct Audit {
+    path: PathBuf,
+    file: Option<File>,
+    /// Lines appended since the last sync.
+    unsynced: bool,
+}
+
+impl Audit {
+    pub fn new(path: PathBuf) -> Self {
+        Self {
+            path,
+            file: None,
+            unsynced: false,
+        }
+    }
+    /// Appends one line; the change it records waits for it.
+    pub fn append(&mut self, entry: &serde_json::Value) -> Result<(), String> {
+        let mut line = entry.to_string();
+        line.push('\n');
+        let path = &self.path;
+        if self.file.is_none() {
+            if let Some(dir) = path.parent() {
+                fs::create_dir_all(dir).map_err(|e| format!("{}: {e}", dir.display()))?;
+            }
+            let file = OpenOptions::new()
+                .create(true)
+                .append(true)
+                .open(path)
+                .map_err(|e| format!("{}: {e}", path.display()))?;
+            self.file = Some(file);
+        }
+        let file = self.file.as_mut().expect("opened above");
+        file.write_all(line.as_bytes())
+            .map_err(|e| format!("{}: {e}", path.display()))?;
+        self.unsynced = true;
+        Ok(())
+    }
+    /// Flushes what was appended to disk (at the end of a tick that appended,
+    /// and when the world closes); nothing when nothing was appended, so a
+    /// quiet tick makes no system call.
+    pub fn sync(&mut self) {
+        if self.unsynced
+            && let Some(f) = &self.file
+        {
+            let _ = f.sync_data();
+            self.unsynced = false;
+        }
+    }
+}
+
+/// `UUID.toString()`: 8-4-4-4-12 lowercase hex digits.
+pub fn uuid_string(u: u128) -> String {
+    let h = format!("{u:032x}");
+    format!(
+        "{}-{}-{}-{}-{}",
+        &h[0..8],
+        &h[8..12],
+        &h[12..16],
+        &h[16..20],
+        &h[20..]
+    )
+}
+
+/// The UUID a [`uuid_string`] wrote.
+pub fn parse_uuid(s: &str) -> Option<u128> {
+    let hex: String = s.chars().filter(|c| *c != '-').collect();
+    (hex.len() == 32)
+        .then(|| u128::from_str_radix(&hex, 16).ok())
+        .flatten()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn scratch(name: &str) -> PathBuf {
+        let dir = std::env::temp_dir().join(format!("smp-store-{name}-{}", std::process::id()));
+        let _ = fs::remove_dir_all(&dir);
+        dir
+    }
+
+    #[test]
+    fn atomic_writes_replace_the_file_and_leave_no_temporary() {
+        let dir = scratch("atomic");
+        let path = dir.join("economy.json");
+        write_atomic(&path, b"one").unwrap();
+        write_atomic(&path, b"two").unwrap();
+        assert_eq!(fs::read(&path).unwrap(), b"two");
+        let names: Vec<_> = fs::read_dir(&dir)
+            .unwrap()
+            .map(|e| e.unwrap().file_name())
+            .collect();
+        assert_eq!(names, ["economy.json"]);
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn a_damaged_document_is_an_error_not_an_empty_one() {
+        let dir = scratch("damaged");
+        let path = dir.join("economy.json");
+        let missing: Vec<u32> = read_json(&path).unwrap();
+        assert!(missing.is_empty());
+        write_atomic(&path, b"{ not json").unwrap();
+        assert!(read_json::<Vec<u32>>(&path).is_err());
+        write_json(&path, &vec![1u32, 2]).unwrap();
+        assert_eq!(read_json::<Vec<u32>>(&path).unwrap(), [1, 2]);
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn the_audit_log_appends_lines() {
+        let dir = scratch("audit");
+        let mut audit = Audit::new(dir.join("audit.log"));
+        audit
+            .append(&serde_json::json!({"kind": "pay", "amount": 5}))
+            .unwrap();
+        audit
+            .append(&serde_json::json!({"kind": "pay", "amount": 6}))
+            .unwrap();
+        audit.sync();
+        let text = fs::read_to_string(dir.join("audit.log")).unwrap();
+        assert_eq!(
+            text,
+            "{\"amount\":5,\"kind\":\"pay\"}\n{\"amount\":6,\"kind\":\"pay\"}\n"
+        );
+        fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn uuids_round_trip() {
+        let u = 0x0000_0000_0000_4000_8000_0000_0000_0001u128;
+        assert_eq!(uuid_string(u), "00000000-0000-4000-8000-000000000001");
+        assert_eq!(parse_uuid(&uuid_string(u)), Some(u));
+        assert_eq!(parse_uuid("nope"), None);
+    }
+}

native/smp/mixins/smp/smp_trade.rs

@@ -0,0 +1,609 @@
+// Player trades (`/trade`): the requests, both sides' offers and
+// confirmations, and the trade menu's layout, with no game types (`S` is the
+// game's item stack). The menu is display only and the offered stacks stay
+// in their owners' inventories: the glue swaps them in one checked step once
+// both have confirmed (`native_exchange_items`), so every way out of a trade
+// (closing, `/trade cancel`, leaving, dying) moves nothing. Added to the game
+// as `game::smp_trade`; also a module of this crate, for its tests.
+
+use super::smp_economy::{Economy, MAX_AMOUNT, Out, Player, parse_amount};
+
+/// How long a request waits for an answer.
+pub const REQUEST_MS: i64 = 60_000;
+/// Stacks one side may offer (the menu's 4 by 4 squares).
+pub const OFFER_SLOTS: usize = 16;
+/// The menu's rows: a 6-row chest.
+pub const ROWS: u8 = 6;
+pub const SIZE: usize = ROWS as usize * 9;
+/// The own side's buttons, and the other side's status.
+pub const MONEY: usize = 37;
+pub const OTHER_MONEY: usize = 43;
+pub const CONFIRM: usize = 45;
+pub const CANCEL: usize = 48;
+pub const OTHER_STATUS: usize = 52;
+
+/// The menu slot of the `i`th square of an offer: the own side on the left
+/// (columns 0 to 3), the other's on the right (5 to 8), four rows.
+pub fn offer_slot(i: usize, own: bool) -> usize {
+    (i / 4) * 9 + i % 4 + if own { 0 } else { 5 }
+}
+
+/// Which square of the own offer a menu slot is.
+fn own_square(slot: usize) -> Option<usize> {
+    let (row, col) = (slot / 9, slot % 9);
+    (row < 4 && col < 4).then_some(row * 4 + col)
+}
+
+/// One side of a trade.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Side<S> {
+    pub uuid: u128,
+    pub name: String,
+    /// Inventory slots offered, with the stack each held when offered: the
+    /// stack it must still hold at the swap.
+    pub offer: Vec<(usize, S)>,
+    pub money: i64,
+    pub confirmed: bool,
+    /// The menu's window, once open.
+    pub window: Option<i32>,
+}
+
+impl<S> Side<S> {
+    fn new(uuid: u128, name: &str) -> Self {
+        Self {
+            uuid,
+            name: name.to_owned(),
+            offer: Vec::new(),
+            money: 0,
+            confirmed: false,
+            window: None,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Trade<S> {
+    pub sides: [Side<S>; 2],
+}
+
+impl<S> Trade<S> {
+    /// The side of `uuid` (0 or 1).
+    pub fn side_of(&self, uuid: u128) -> Option<usize> {
+        self.sides.iter().position(|s| s.uuid == uuid)
+    }
+    fn unconfirm(&mut self) {
+        for s in &mut self.sides {
+            s.confirmed = false;
+        }
+    }
+}
+
+struct Request {
+    from: u128,
+    from_name: String,
+    to: u128,
+    at: i64,
+}
+
+/// Finds a player who is on by name: their uuid, name, and whether they
+/// may trade (survival or adventure).
+pub type Online<'a> = dyn Fn(&str) -> Option<(u128, String, bool)> + 'a;
+
+/// What the glue does for the trades.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Act {
+    /// Open (or show again) the trade menu of the trade `uuid` is in.
+    Show(u128),
+    /// Close the player's trade menu (their trade ended).
+    Close(u128),
+    /// Both confirmed: swap the trade `uuid` is in.
+    Settle(u128),
+}
+
+/// What a menu cell shows; the glue makes the item.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Cell<S> {
+    Empty,
+    Stack(S),
+    Divider,
+    /// A side's money: whether it is the viewer's, the amount.
+    Money(bool, i64),
+    /// The viewer's confirm button: confirmed or not.
+    Confirm(bool),
+    Cancel,
+    /// The other side: their name, confirmed or not.
+    Other(String, bool),
+}
+
+/// The open trades and the requests waiting.
+pub struct Trades<S> {
+    requests: Vec<Request>,
+    pub open: Vec<Trade<S>>,
+}
+
+impl<S> Default for Trades<S> {
+    fn default() -> Self {
+        Self {
+            requests: Vec::new(),
+            open: Vec::new(),
+        }
+    }
+}
+
+impl<S: Clone + PartialEq> Trades<S> {
+    pub fn trade_of(&self, uuid: u128) -> Option<&Trade<S>> {
+        self.open.iter().find(|t| t.side_of(uuid).is_some())
+    }
+    fn index_of(&self, uuid: u128) -> Option<usize> {
+        self.open.iter().position(|t| t.side_of(uuid).is_some())
+    }
+
+    /// Ends the trade `uuid` is in, nothing moved: its players' menus close
+    /// and both are told why.
+    pub fn end(&mut self, uuid: u128, why: &str) -> (Vec<Out>, Vec<Act>) {
+        let Some(i) = self.index_of(uuid) else {
+            return (Vec::new(), Vec::new());
+        };
+        let t = self.open.remove(i);
+        let mut out = Vec::new();
+        let mut acts = Vec::new();
+        for s in &t.sides {
+            out.push(Out::Tell(
+                s.uuid,
+                format!("Trade cancelled: {why}. Nothing was exchanged."),
+            ));
+            acts.push(Act::Close(s.uuid));
+        }
+        (out, acts)
+    }
+
+    /// `/trade <player>`, `/trade accept|deny [player]`, `/trade cancel`,
+    /// `/trade money <amount>`; None for another command. `online` finds a
+    /// player who is on by name (uuid, name, may trade).
+    pub fn command(
+        &mut self,
+        economy: &Economy,
+        me: &Player,
+        may_trade: bool,
+        online: &Online,
+        now: i64,
+        line: &str,
+    ) -> Option<(Vec<Out>, Vec<Act>)> {
+        let mut words = line.split_whitespace();
+        if words.next()? != "trade" {
+            return None;
+        }
+        self.requests.retain(|r| now - r.at < REQUEST_MS);
+        let err = |s: &str| Some((vec![Out::Error(s.to_owned())], Vec::new()));
+        let usage = "Usage: /trade <player>, /trade accept|deny [player], /trade cancel, /trade money <amount>";
+        let arg = words.next();
+        let rest = words.next();
+        match arg {
+            None => err(usage),
+            Some("cancel") => {
+                if self.index_of(me.uuid).is_some() {
+                    return Some(self.end(me.uuid, &format!("{} cancelled", me.name)));
+                }
+                let before = self.requests.len();
+                self.requests.retain(|r| r.from != me.uuid);
+                if self.requests.len() < before {
+                    Some((
+                        vec![Out::Reply("Your trade request is withdrawn.".into())],
+                        Vec::new(),
+                    ))
+                } else {
+                    err("You have no trade to cancel.")
+                }
+            }
+            Some("money") => {
+                let Some(i) = self.index_of(me.uuid) else {
+                    return err("You are not in a trade.");
+                };
+                let Some(amount) = rest
+                    .and_then(parse_amount)
+                    .or(rest.filter(|r| *r == "0").map(|_| 0))
+                else {
+                    return err("Usage: /trade money <amount> (0 to offer none)");
+                };
+                if amount > MAX_AMOUNT || amount > economy.balance(me.uuid) {
+                    return err(&format!(
+                        "You only have {}.",
+                        economy.money(economy.balance(me.uuid))
+                    ));
+                }
+                let t = &mut self.open[i];
+                let side = t.side_of(me.uuid).expect("found");
+                t.sides[side].money = amount;
+                t.unconfirm();
+                let other = t.sides[1 - side].uuid;
+                Some((
+                    vec![
+                        Out::Reply(format!("You offer {}.", economy.money(amount))),
+                        Out::Tell(
+                            other,
+                            format!("{} offers {}.", me.name, economy.money(amount)),
+                        ),
+                    ],
+                    vec![Act::Show(me.uuid), Act::Show(other)],
+                ))
+            }
+            Some(verb @ ("accept" | "deny")) => {
+                let pick = |r: &&Request| {
+                    r.to == me.uuid && rest.is_none_or(|n| r.from_name.eq_ignore_ascii_case(n))
+                };
+                let Some(r) = self.requests.iter().rfind(pick) else {
+                    return err("You have no trade request to answer.");
+                };
+                let (from, from_name) = (r.from, r.from_name.clone());
+                self.requests
+                    .retain(|r| !(r.from == from && r.to == me.uuid));
+                if verb == "deny" {
+                    return Some((
+                        vec![
+                            Out::Reply(format!("You refused {from_name}'s trade.")),
+                            Out::Tell(from, format!("{} refused your trade.", me.name)),
+                        ],
+                        Vec::new(),
+                    ));
+                }
+                if !may_trade {
+                    return err("You can trade only in survival or adventure mode.");
+                }
+                let Some((_, _, they_may)) = online(&from_name).filter(|(u, _, _)| *u == from)
+                else {
+                    return err(&format!("{from_name} is no longer here."));
+                };
+                if !they_may {
+                    return err(&format!("{from_name} can't trade in their game mode."));
+                }
+                if self.index_of(me.uuid).is_some() || self.index_of(from).is_some() {
+                    return err("One of you is already in a trade.");
+                }
+                self.requests
+                    .retain(|r| r.from != from && r.from != me.uuid);
+                self.open.push(Trade {
+                    sides: [Side::new(from, &from_name), Side::new(me.uuid, &me.name)],
+                });
+                Some((Vec::new(), vec![Act::Show(from), Act::Show(me.uuid)]))
+            }
+            Some(name) => {
+                if rest.is_some() {
+                    return err(usage);
+                }
+                if !may_trade {
+                    return err("You can trade only in survival or adventure mode.");
+                }
+                let Some((to, to_name, they_may)) = online(name) else {
+                    return err(&format!("{name} is not here."));
+                };
+                if to == me.uuid {
+                    return err("You can't trade with yourself.");
+                }
+                if !they_may {
+                    return err(&format!("{to_name} can't trade in their game mode."));
+                }
+                if self.index_of(me.uuid).is_some() || self.index_of(to).is_some() {
+                    return err("One of you is already in a trade.");
+                }
+                // A request back is an answer.
+                if self
+                    .requests
+                    .iter()
+                    .any(|r| r.from == to && r.to == me.uuid)
+                {
+                    return self.command(
+                        economy,
+                        me,
+                        may_trade,
+                        online,
+                        now,
+                        &format!("trade accept {to_name}"),
+                    );
+                }
+                self.requests.retain(|r| r.from != me.uuid);
+                self.requests.push(Request {
+                    from: me.uuid,
+                    from_name: me.name.clone(),
+                    to,
+                    at: now,
+                });
+                Some((
+                    vec![
+                        Out::Reply(format!("Trade request sent to {to_name}.")),
+                        Out::Tell(
+                            to,
+                            format!(
+                                "{} wants to trade with you: /trade accept {} or /trade deny {} (60 s).",
+                                me.name, me.name, me.name
+                            ),
+                        ),
+                    ],
+                    Vec::new(),
+                ))
+            }
+        }
+    }
+
+    /// A click in `uuid`'s trade menu: on their inventory's slot `inventory`
+    /// holding `stack` (offered whole), or on the menu's slot `menu`.
+    pub fn click(
+        &mut self,
+        uuid: u128,
+        menu: Option<usize>,
+        inventory: Option<(usize, S)>,
+    ) -> (Vec<Out>, Vec<Act>) {
+        let Some(i) = self.index_of(uuid) else {
+            return (Vec::new(), Vec::new());
+        };
+        let t = &mut self.open[i];
+        let me = t.side_of(uuid).expect("found");
+        let other = t.sides[1 - me].uuid;
+        let shown = vec![Act::Show(uuid), Act::Show(other)];
+        if let Some((slot, stack)) = inventory {
+            let side = &mut t.sides[me];
+            if side.offer.iter().any(|(s, _)| *s == slot) {
+                return (Vec::new(), Vec::new());
+            }
+            if side.offer.len() >= OFFER_SLOTS {
+                return (
+                    vec![Out::Tell(
+                        uuid,
+                        format!("You can offer {OFFER_SLOTS} stacks at most."),
+                    )],
+                    Vec::new(),
+                );
+            }
+            side.offer.push((slot, stack));
+            t.unconfirm();
+            return (Vec::new(), shown);
+        }
+        match menu {
+            Some(CANCEL) => {
+                let why = format!("{} cancelled", t.sides[me].name);
+                self.end(uuid, &why)
+            }
+            Some(CONFIRM) => {
+                t.sides[me].confirmed = !t.sides[me].confirmed;
+                if t.sides.iter().all(|s| s.confirmed) {
+                    (Vec::new(), vec![Act::Settle(uuid)])
+                } else {
+                    (Vec::new(), shown)
+                }
+            }
+            Some(slot) => match own_square(slot).filter(|&q| q < t.sides[me].offer.len()) {
+                Some(q) => {
+                    t.sides[me].offer.remove(q);
+                    t.unconfirm();
+                    (Vec::new(), shown)
+                }
+                None => (Vec::new(), Vec::new()),
+            },
+            None => (Vec::new(), Vec::new()),
+        }
+    }
+
+    /// Checks `uuid`'s offer against their inventory now (`stacks`, by
+    /// slot): a stack that changed (used, dropped, grown by a pickup) leaves
+    /// the offer and both confirmations are cleared. Whether anything left.
+    pub fn refresh(&mut self, uuid: u128, stacks: &[Option<S>]) -> bool {
+        let Some(i) = self.index_of(uuid) else {
+            return false;
+        };
+        let t = &mut self.open[i];
+        let me = t.side_of(uuid).expect("found");
+        let before = t.sides[me].offer.len();
+        t.sides[me]
+            .offer
+            .retain(|(slot, s)| stacks.get(*slot).and_then(|x| x.as_ref()) == Some(s));
+        let changed = t.sides[me].offer.len() < before;
+        if changed {
+            t.unconfirm();
+        }
+        changed
+    }
+
+    /// What `uuid`'s trade menu shows, slot by slot.
+    pub fn layout(&self, uuid: u128) -> Vec<Cell<S>> {
+        let mut cells = vec![Cell::Empty; SIZE];
+        let Some(t) = self.trade_of(uuid) else {
+            return cells;
+        };
+        let me = t.side_of(uuid).expect("found");
+        let (mine, theirs) = (&t.sides[me], &t.sides[1 - me]);
+        for row in 0..ROWS as usize {
+            cells[row * 9 + 4] = Cell::Divider;
+        }
+        for (i, (_, s)) in mine.offer.iter().enumerate() {
+            cells[offer_slot(i, true)] = Cell::Stack(s.clone());
+        }
+        for (i, (_, s)) in theirs.offer.iter().enumerate() {
+            cells[offer_slot(i, false)] = Cell::Stack(s.clone());
+        }
+        cells[MONEY] = Cell::Money(true, mine.money);
+        cells[OTHER_MONEY] = Cell::Money(false, theirs.money);
+        cells[CONFIRM] = Cell::Confirm(mine.confirmed);
+        cells[CANCEL] = Cell::Cancel;
+        cells[OTHER_STATUS] = Cell::Other(theirs.name.clone(), theirs.confirmed);
+        cells
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const A: u128 = 1;
+    const B: u128 = 2;
+    type S = (&'static str, u32);
+
+    fn economy() -> Economy {
+        // One folder per call: the tests run side by side.
+        static N: std::sync::atomic::AtomicU32 = std::sync::atomic::AtomicU32::new(0);
+        let n = N.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+        let dir = std::env::temp_dir().join(format!("smp-trade-{}-{n}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let mut e = Economy::open(&dir, Default::default()).unwrap();
+        e.seen(A, "Alex");
+        e.seen(B, "Steve");
+        e.adjust("eco_give", A, 100, "test").unwrap();
+        e
+    }
+    fn player(uuid: u128) -> Player {
+        Player {
+            uuid,
+            name: if uuid == A { "Alex" } else { "Steve" }.into(),
+            level: 0,
+        }
+    }
+    fn online(name: &str) -> Option<(u128, String, bool)> {
+        match name.to_ascii_lowercase().as_str() {
+            "alex" => Some((A, "Alex".into(), true)),
+            "steve" => Some((B, "Steve".into(), true)),
+            _ => None,
+        }
+    }
+    fn open() -> (Economy, Trades<S>) {
+        let e = economy();
+        let mut t = Trades::default();
+        t.command(&e, &player(A), true, &online, 0, "trade Steve")
+            .unwrap();
+        let (_, acts) = t
+            .command(&e, &player(B), true, &online, 1_000, "trade accept")
+            .unwrap();
+        assert_eq!(acts, [Act::Show(A), Act::Show(B)]);
+        (e, t)
+    }
+
+    #[test]
+    fn a_request_opens_a_trade_once_accepted() {
+        let (_, t) = open();
+        assert_eq!(t.open.len(), 1);
+        let cells = t.layout(B);
+        assert_eq!(cells[OTHER_STATUS], Cell::Other("Alex".into(), false));
+        assert_eq!(cells[CONFIRM], Cell::Confirm(false));
+    }
+
+    #[test]
+    fn requests_expire_and_can_be_refused() {
+        let e = economy();
+        let mut t: Trades<S> = Trades::default();
+        t.command(&e, &player(A), true, &online, 0, "trade Steve")
+            .unwrap();
+        let (out, _) = t
+            .command(&e, &player(B), true, &online, REQUEST_MS, "trade accept")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(_)));
+        t.command(&e, &player(A), true, &online, 0, "trade Steve")
+            .unwrap();
+        t.command(&e, &player(B), true, &online, 10, "trade deny Alex")
+            .unwrap();
+        let (out, _) = t
+            .command(&e, &player(B), true, &online, 20, "trade accept")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(_)));
+        // Creative players don't trade; nor does a player with themselves.
+        let (out, _) = t
+            .command(&e, &player(A), false, &online, 0, "trade Steve")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(_)));
+        let (out, _) = t
+            .command(&e, &player(A), true, &online, 0, "trade Alex")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(_)));
+        assert!(t.open.is_empty());
+    }
+
+    #[test]
+    fn any_change_clears_both_confirmations() {
+        let (e, mut t) = open();
+        t.click(A, None, Some((3, ("minecraft:diamond", 5))));
+        t.click(A, Some(CONFIRM), None);
+        t.click(B, Some(CONFIRM), None);
+        // Both confirmed: settled; a click after the settle's failure, or a
+        // change, needs both again.
+        assert_eq!(t.open[0].sides.iter().filter(|s| s.confirmed).count(), 2);
+        t.click(B, None, Some((0, ("minecraft:emerald", 1))));
+        assert!(t.open[0].sides.iter().all(|s| !s.confirmed));
+        t.click(A, Some(CONFIRM), None);
+        t.command(&e, &player(B), true, &online, 0, "trade money 0")
+            .unwrap();
+        assert!(t.open[0].sides.iter().all(|s| !s.confirmed));
+        // Taking a stack back out of the offer.
+        t.click(A, Some(CONFIRM), None);
+        t.click(A, Some(offer_slot(0, true)), None);
+        assert!(t.open[0].sides[0].offer.is_empty());
+        assert!(!t.open[0].sides[0].confirmed);
+    }
+
+    #[test]
+    fn the_second_confirmation_settles() {
+        let (_, mut t) = open();
+        t.click(A, None, Some((3, ("minecraft:diamond", 5))));
+        assert_eq!(
+            t.click(A, Some(CONFIRM), None).1,
+            [Act::Show(A), Act::Show(B)]
+        );
+        assert_eq!(t.click(B, Some(CONFIRM), None).1, [Act::Settle(B)]);
+    }
+
+    #[test]
+    fn an_offer_is_one_slot_once_and_sixteen_at_most() {
+        let (_, mut t) = open();
+        t.click(A, None, Some((3, ("minecraft:diamond", 5))));
+        t.click(A, None, Some((3, ("minecraft:diamond", 5))));
+        assert_eq!(t.open[0].sides[0].offer.len(), 1);
+        for slot in 10..30 {
+            t.click(A, None, Some((slot, ("minecraft:dirt", 1))));
+        }
+        assert_eq!(t.open[0].sides[0].offer.len(), OFFER_SLOTS);
+        assert_eq!(
+            t.layout(B)[offer_slot(0, false)],
+            Cell::Stack(("minecraft:diamond", 5))
+        );
+    }
+
+    #[test]
+    fn a_stack_that_changed_leaves_the_offer() {
+        let (_, mut t) = open();
+        t.click(A, None, Some((3, ("minecraft:diamond", 5))));
+        t.click(A, None, Some((4, ("minecraft:dirt", 1))));
+        t.click(A, Some(CONFIRM), None);
+        let mut inv: Vec<Option<S>> = vec![None; 36];
+        inv[3] = Some(("minecraft:diamond", 5));
+        inv[4] = Some(("minecraft:dirt", 1));
+        assert!(!t.refresh(A, &inv));
+        assert!(t.open[0].sides[0].confirmed);
+        // A pickup grew the diamonds.
+        inv[3] = Some(("minecraft:diamond", 6));
+        assert!(t.refresh(A, &inv));
+        assert_eq!(t.open[0].sides[0].offer, [(4, ("minecraft:dirt", 1))]);
+        assert!(!t.open[0].sides[0].confirmed);
+    }
+
+    #[test]
+    fn every_way_out_ends_the_trade_with_nothing_moved() {
+        // Cancel button, /trade cancel; closing and leaving go through
+        // `end` from the glue.
+        let (e, mut t) = open();
+        let (out, acts) = t.click(B, Some(CANCEL), None);
+        assert_eq!(acts, [Act::Close(A), Act::Close(B)]);
+        assert!(matches!(&out[0], Out::Tell(A, s) if s.contains("Nothing was exchanged")));
+        assert!(t.open.is_empty());
+        let (_, mut t) = open();
+        t.command(&e, &player(A), true, &online, 0, "trade cancel")
+            .unwrap();
+        assert!(t.open.is_empty());
+        let (_, mut t) = open();
+        t.end(B, "Steve left");
+        assert!(t.open.is_empty());
+        // Money beyond the balance is refused when offered.
+        let (_, mut t) = open();
+        let (out, _) = t
+            .command(&e, &player(A), true, &online, 0, "trade money 101")
+            .unwrap();
+        assert!(matches!(&out[0], Out::Error(_)));
+        t.command(&e, &player(A), true, &online, 0, "trade money 100")
+            .unwrap();
+        assert_eq!(t.open[0].sides[0].money, 100);
+    }
+}

native/smp/mixins/smp/tick.rs

@@ -0,0 +1,12 @@
+// The end of each server tick: the SMP's accounts and files.
+fn smp_server_tick(
+    game: &mut crate::game::Game<'_>,
+    phase: crate::game::native_lifecycle::ServerTickPhase,
+) {
+    if matches!(
+        phase,
+        crate::game::native_lifecycle::ServerTickPhase::ServerTickEnd { .. }
+    ) {
+        crate::game::smp_glue::tick(game);
+    }
+}

native/smp/proof.py

@@ -0,0 +1,414 @@
+"""The SMP on a real dedicated server: the built game runs `--dedicated` with the mod, and two real clients (Alex and
+Steve, `horizon-ctl --offscreen`) join it. Checked from the clients' own chat and from the files the server wrote:
+
+- the economy opens an account for each player (config.json written with its defaults, then economy.json);
+- /balance, /pay (the payer's answer and the payee's line), refused payments (too much, to oneself, unknown name);
+- /baltop; /eco is refused below level 3 and works for an operator (made one from the server's console);
+- the commands are in each player's command tree (the chat box's suggestions);
+- the market (Steve in survival, items given from the console): /worth, /sell <item>, /sell hand, /buy, with the
+  items gone from or in his inventory as his client sees it; a creative player can't sell;
+- trades (`/trade`, the server's chest menu clicked from each client): closing the menu, a full inventory, the
+  cancel button, dying and leaving each end or refuse a trade with nothing moved (each player's items counted from
+  their own client); a change of offer clears the other's confirmation; a confirmed trade swaps the items and money;
+- coinflips (turned on in config.json before the first start, the other settings filled in): the stake is held from
+  the offer, the winner gets both, the limits and the cooldown refuse, and a stake left waiting when the server stops
+  comes back; the money in the game stays the same throughout;
+- the lottery: two players' tickets held, one drawn after `lottery_seconds`, the winner announced to everyone and paid
+  the pot;
+- after the server stops cleanly and starts again, the balances are the same, and audit.log holds every change.
+
+Everything runs in fresh temporary folders (the server's, each client's home, launcher and XDG folders), no audio.
+"""
+import json
+import os
+import shutil
+import socket
+import subprocess
+import tempfile
+import threading
+import time
+from pathlib import Path
+
+PROPERTIES = {
+    "online-mode": "false", "white-list": "false", "enforce-secure-profile": "false", "level-type": "minecraft\\:flat", "spawn-protection": "0", "max-players": "4",
+    "view-distance": "4", "simulation-distance": "4", "generate-structures": "false", "enable-command-block": "false",
+    "difficulty": "peaceful", "spawn-monsters": "false",
+}
+
+
+def free_port():
+    with socket.socket() as s:
+        s.bind(("127.0.0.1", 0))
+        return s.getsockname()[1]
+
+
+def scratch_env(root):
+    env = dict(os.environ, HORIZON_NO_AUDIO="1", HORIZON_LAUNCHER_NO_SELF_UPDATE="1")
+    for key in ("HORIZON_HOME", "HORIZON_LAUNCHER_HOME", "XDG_DATA_HOME", "XDG_CONFIG_HOME"):
+        path = root / key.lower()
+        path.mkdir(parents=True, exist_ok=True)
+        env[key] = str(path)
+    return env
+
+
+class Server:
+    """`horizon-client --dedicated --nogui` in a scratch server folder, its console on stdin."""
+
+    def __init__(self, game, resources, folder, port):
+        self.folder, self.lines, self.game, self.resources, self.port = folder, [], game, resources, port
+        folder.mkdir(parents=True, exist_ok=True)
+        props = dict(PROPERTIES, **{"server-port": str(port)})
+        (folder / "server.properties").write_text("".join(f"{k}={v}\n" for k, v in props.items()))
+        (folder / "eula.txt").write_text("eula=true\n")
+        self.env = scratch_env(folder.parent / "server-env")
+
+    def start(self):
+        self.lines = []
+        self.process = subprocess.Popen(
+            [str(self.game), "--resources", str(self.resources), "--dedicated", "--nogui"], cwd=self.folder,
+            env=self.env, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
+        threading.Thread(target=self._read, daemon=True).start()
+        self.wait_for("Done (", 600)
+
+    def _read(self):
+        for line in self.process.stdout:
+            self.lines.append(line.rstrip("\n"))
+
+    def wait_for(self, text, timeout=120):
+        end = time.time() + timeout
+        while time.time() < end:
+            if any(text in line for line in self.lines):
+                return
+            if self.process.poll() is not None:
+                break
+            time.sleep(0.2)
+        raise AssertionError(f"server: no {text!r} in {timeout} s; last lines: {self.lines[-30:]}")
+
+    def console(self, line):
+        self.process.stdin.write(line + "\n")
+        self.process.stdin.flush()
+
+    def stop(self):
+        if self.process.poll() is None:
+            self.console("stop")
+            try:
+                self.process.wait(120)
+            except subprocess.TimeoutExpired:
+                self.process.kill()
+        return self.lines
+
+
+class Client:
+    """A real client under horizon-ctl, joined to the server as `name`."""
+
+    def __init__(self, ctl, resources, name, root):
+        self.ctl, self.name, self.resources = ctl, name, resources
+        self.home = root / name
+        self.env = scratch_env(self.home)
+        self.socket = str(self.home / "ctl.sock")
+
+    def run(self, *args, check=True):
+        done = subprocess.run([str(self.ctl), "--socket", self.socket, *map(str, args)], env=self.env,
+                              cwd=self.home, capture_output=True, text=True, timeout=600)
+        if check and done.returncode:
+            raise AssertionError(f"{self.name}: {args}: {done.stdout[-400:]} {done.stderr[-400:]}")
+        try:
+            return json.loads(done.stdout.strip().splitlines()[-1])
+        except (json.JSONDecodeError, IndexError):
+            return done.stdout
+
+    def join(self, port):
+        self.run("launch", "--offscreen", "--resources", self.resources)
+        self.run("connect", f"127.0.0.1:{port}", self.name)
+        self.run("wait-for", "loaded", "--timeout", 300)
+        time.sleep(2)
+
+    def say(self, line):
+        """A command typed in chat; returns the chat lines it brought."""
+        before = len(self.chat())
+        self.run("chat", line)
+        time.sleep(1.5)
+        return self.chat()[before:]
+
+    def chat(self):
+        """Every chat line so far, oldest first (`messages` answers newest first)."""
+        reply = self.run("messages", 500)
+        return list(reversed(reply.get("chat", [])))
+
+    def quit(self):
+        self.run("quit", check=False)
+
+    def screen(self):
+        return self.run("screen")
+
+    def menu(self):
+        """The open server menu's items by its own slot (horizon-ctl numbers them from 300)."""
+        return {e["slot"] - 300: e for e in self.screen().get("slots", []) if e.get("item") and e["slot"] >= 300}
+
+    def slot_of(self, item):
+        """The inventory slot (0..36) holding `item`, as the open screen shows it."""
+        return next(e["slot"] for e in self.screen().get("slots", []) if e.get("item") == item and e["slot"] < 36)
+
+    def count(self, item):
+        counts = self.run("inventory").get("counts", {})
+        return counts.get(item, counts.get(item.removeprefix("minecraft:"), 0))
+
+    def click(self, slot):
+        self.run("click-slot", slot)
+        time.sleep(1)
+
+
+CONFIRM, CANCEL, THEIR_FIRST = 300 + 45, 300 + 48, 5
+
+
+def open_trade(alex, steve):
+    assert any("Trade request sent to Steve." in l for l in alex.say("/trade Steve"))
+    assert any("Alex wants to trade with you" in l for l in steve.chat()[-3:])
+    steve.say("/trade accept")
+    time.sleep(1)
+    for c, other in ((alex, "Steve"), (steve, "Alex")):
+        menu = c.menu()
+        assert menu.get(45, {}).get("item") == "minecraft:lime_stained_glass_pane", (c.name, menu)
+        title = "".join(s["text"] for s in c.screen().get("title", []))
+        assert title == f"Trade with {other}", title
+
+
+def coinflips(alex, steve):
+    """Alex 415, Steve 400. Returns what was seen and whether Alex won."""
+    results = {}
+    results["limits"] = alex.say("/coinflip 5")
+    assert any("A coinflip is 10 coins to 1,000 coins." in l for l in results["limits"]), results
+    results["offer"] = alex.say("/coinflip 100 Steve")
+    assert any("Coinflip of 100 coins offered to Steve" in l for l in results["offer"]), results
+    assert any("Balance: 315 coins" in l for l in alex.say("/balance")), "the stake is held"
+    assert any("Alex offers you a coinflip of 100 coins" in l for l in steve.chat()[-3:])
+    steve.say("/coinflip accept Alex")
+    time.sleep(1)
+    results["alex_saw"] = alex.chat()[-1:]
+    alex_wins = any("you won 200 coins" in l for l in results["alex_saw"])
+    assert alex_wins or any("you lost 100 coins" in l for l in results["alex_saw"]), results
+    steve_saw = steve.chat()[-2:]
+    assert any(("you lost 100 coins" if alex_wins else "you won 200 coins") in l for l in steve_saw), steve_saw
+    assert any(f"Balance: {415 + (100 if alex_wins else -100)} coins" in l for l in alex.say("/balance"))
+    assert any(f"Balance: {400 + (-100 if alex_wins else 100)} coins" in l for l in steve.say("/balance"))
+    results["cooldown"] = steve.say("/coinflip 50")
+    assert any("before your next coinflip" in l for l in results["cooldown"]), results
+    time.sleep(20)
+    assert any("Coinflip of 50 coins offered" in l for l in steve.say("/coinflip 50")), "after the cooldown"
+    return results, alex_wins
+
+
+def lottery(alex, steve, alex_wins):
+    """Alex buys 3 tickets, Steve 2; the round draws 30 s after the first. Returns what was seen, whether Alex won."""
+    results = {}
+    alex_had = 415 + (100 if alex_wins else -100)
+    steve_had = 400 + (-100 if alex_wins else 100) - 50  # his coinflip of 50 is still held
+    results["buy"] = alex.say("/lottery buy 3")
+    assert any("You bought 3 ticket(s) for 30 coins; the pot is 30 coins" in l for l in results["buy"]), results
+    assert any("the pot is 50 coins" in l for l in steve.say("/lottery buy 2"))
+    assert any(f"Balance: {alex_had - 30} coins" in l for l in alex.say("/balance")), "the tickets are held"
+    results["status"] = steve.say("/lottery")
+    assert any("Lottery: pot 50 coins, 2 ticket(s) of yours" in l for l in results["status"]), results
+    time.sleep(32)
+    results["draw"] = [l for l in alex.chat()[-3:] if l.startswith("Lottery:")]
+    assert len(results["draw"]) == 1 and "won 50 coins" in results["draw"][0], results
+    assert results["draw"][0] in steve.chat()[-3:], "everyone hears the draw"
+    alex_lotto = results["draw"][0].startswith("Lottery: Alex won")
+    assert any(f"Balance: {alex_had - 30 + (50 if alex_lotto else 0)} coins" in l for l in alex.say("/balance"))
+    assert any(f"Balance: {steve_had - 20 + (0 if alex_lotto else 50)} coins" in l for l in steve.say("/balance"))
+    return results, alex_lotto
+
+
+def trades(server, alex, steve, port, ctl, resources, root):
+    """Every way out of a trade, then one that goes through. Alex: 10 diamonds; Steve: 5 emeralds, 5 torches."""
+    results = {}
+    items = lambda: (alex.count("minecraft:diamond"), alex.count("minecraft:emerald"),
+                     steve.count("minecraft:diamond"), steve.count("minecraft:emerald"))
+    assert items() == (10, 0, 0, 5), items()
+    # Closing the menu.
+    open_trade(alex, steve)
+    alex.click(alex.slot_of("minecraft:diamond"))
+    shown = steve.menu().get(THEIR_FIRST, {})
+    assert (shown.get("item"), shown.get("count")) == ("minecraft:diamond", 10), shown
+    assert alex.count("minecraft:diamond") == 10, "offered stacks stay in the inventory"
+    alex.run("close")
+    time.sleep(1.5)
+    results["closed"] = steve.chat()[-2:]
+    assert any("Trade cancelled: Alex closed the trade. Nothing was exchanged." in l for l in results["closed"])
+    assert not steve.menu(), "the other's menu closes too"
+    assert items() == (10, 0, 0, 5), items()
+    # A full inventory: Steve can't take the diamonds; nothing moves, the trade stays open, both must confirm again.
+    server.console("give Steve minecraft:dirt 2176")
+    time.sleep(2)
+    open_trade(alex, steve)
+    alex.click(alex.slot_of("minecraft:diamond"))
+    alex.click(CONFIRM)
+    steve.click(CONFIRM)
+    results["full"] = alex.chat()[-2:]
+    assert any("The trade didn't go through: the second player has no room." in l for l in results["full"]), results
+    assert alex.menu().get(45, {}).get("item") == "minecraft:lime_stained_glass_pane", "confirmations cleared"
+    assert items() == (10, 0, 0, 5), items()
+    # The cancel button.
+    steve.click(CANCEL)
+    assert any("Trade cancelled: Steve cancelled." in l for l in alex.chat()[-2:])
+    server.console("clear Steve minecraft:dirt")
+    time.sleep(1)
+    # Through: Alex's diamonds for Steve's emeralds and 35 coins. Steve's money offer clears Alex's confirmation.
+    open_trade(alex, steve)
+    alex.click(alex.slot_of("minecraft:diamond"))
+    steve.click(steve.slot_of("minecraft:emerald"))
+    alex.click(CONFIRM)
+    assert alex.menu()[45]["item"] == "minecraft:lime_concrete"
+    assert steve.menu()[52]["item"] == "minecraft:lime_concrete", "Steve sees Alex confirmed"
+    steve.say("/trade money 35")
+    assert alex.menu()[45]["item"] == "minecraft:lime_stained_glass_pane", "a change clears the confirmation"
+    alex.click(CONFIRM)
+    steve.click(CONFIRM)
+    time.sleep(1)
+    results["done"] = alex.chat()[-2:]
+    assert any("Trade with Steve done" in l for l in results["done"]), results
+    assert items() == (0, 5, 10, 0), items()
+    assert any("Balance: 415 coins" in l for l in alex.say("/balance"))
+    assert any("Balance: 400 coins" in l for l in steve.say("/balance"))
+    # Dying (inventories kept, so a duplicate would show): Alex's death ends it, nothing moved.
+    server.console("gamerule keep_inventory true")
+    time.sleep(1)
+    open_trade(alex, steve)
+    alex.click(alex.slot_of("minecraft:emerald"))
+    server.console("kill Alex")
+    time.sleep(2)
+    results["death"] = steve.chat()[-2:]
+    assert any("Trade cancelled" in l for l in results["death"]), results
+    alex.run("respawn")
+    time.sleep(2)
+    assert items() == (0, 5, 10, 0), items()
+    # Leaving: Steve quits mid-trade; nothing moved, his items are his when he comes back.
+    open_trade(alex, steve)
+    steve.click(steve.slot_of("minecraft:diamond"))
+    steve.quit()
+    time.sleep(3)
+    results["left"] = alex.chat()[-2:]
+    assert any("Trade cancelled" in l for l in results["left"]), results
+    assert not alex.menu()
+    steve = Client(ctl, resources, "Steve2", root)
+    steve.name = "Steve"
+    steve.join(port)
+    assert items() == (0, 5, 10, 0), items()
+    return results, steve
+
+
+def run(ctl, resources, out):
+    out = Path(out)
+    out.mkdir(parents=True, exist_ok=True)
+    game = Path(ctl).with_name("horizon-client")
+    root = Path(tempfile.mkdtemp(prefix="smp-proof-"))
+    port = free_port()
+    server = Server(game, resources, root / "server", port)
+    alex = Client(ctl, resources, "Alex", root)
+    steve = Client(ctl, resources, "Steve", root)
+    results = {}
+    try:
+        data = server.folder / "world" / "horizon-smp"
+        data.mkdir(parents=True)
+        (data / "config.json").write_text(json.dumps({"gambling": {"enabled": True, "cooldown_seconds": 20,
+                                                                         "lottery_seconds": 30}}))
+        server.start()
+        alex.join(port)
+        steve.join(port)
+        time.sleep(2)
+        config = json.loads((data / "config.json").read_text())
+        results["config_keys"] = sorted(config)
+        assert results["config_keys"] == ["currency", "gambling", "market", "starting_balance"], config
+        assert config["gambling"] == {"enabled": True, "min_bet": 10, "max_bet": 1000, "cooldown_seconds": 20,
+                                      "offer_seconds": 60, "fee_percent": 0, "ticket_price": 10,
+                                      "max_tickets": 100, "lottery_seconds": 30}, config
+        assert config["market"]["items"]["minecraft:diamond"] == {"buy": 400, "sell": 100}, config
+        server.console("op Alex")
+        time.sleep(1)
+        alex.say("/eco give Alex 500")
+        results["balance"] = alex.say("/balance")
+        assert any("Balance: 500 coins" in l for l in results["balance"]), results
+        results["pay"] = alex.say("/pay Steve 120")
+        assert any("You paid 120 coins to Steve. Balance: 380 coins" in l for l in results["pay"]), results
+        results["paid"] = steve.chat()[-3:]
+        assert any("Alex paid you 120 coins." in l for l in results["paid"]), results
+        results["refused"] = [alex.say(l) for l in ("/pay Steve 9999", "/pay Alex 1", "/pay Nobody 1")]
+        for lines, error in zip(results["refused"], ("You only have 380 coins.", "You can't pay yourself.",
+                                                     "No player named Nobody has an account.")):
+            assert any(error in l for l in lines), results["refused"]
+        results["eco_refused"] = steve.say("/eco give Steve 1000")
+        assert not any("now has" in l for l in results["eco_refused"]), results
+        results["baltop"] = steve.say("/baltop")
+        assert any("1. Alex: 380 coins" in l for l in results["baltop"]), results
+        assert any("2. Steve: 120 coins" in l for l in results["baltop"]), results
+        server.console("give Steve minecraft:diamond 3")
+        server.console("give Steve minecraft:wheat 20")
+        time.sleep(2)
+        results["worth"] = steve.say("/worth diamond")
+        assert any("diamond: the market pays 100 coins each, sells it for 400 coins each." in l
+                   for l in results["worth"]), results
+        results["sell_wheat"] = steve.say("/sell wheat")
+        assert any("Sold 20 wheat for 20 coins." in l for l in results["sell_wheat"]), results
+        results["sell_hand"] = steve.say("/sell hand")
+        assert any("Sold 3 diamond for 300 coins." in l for l in results["sell_hand"]), results
+        results["buy"] = steve.say("/buy torch 5")
+        assert any("Bought 5 torch for 5 coins." in l for l in results["buy"]), results
+        time.sleep(1)
+        counts = steve.run("inventory").get("counts", {})
+        results["steve_items"] = counts
+        have = lambda item: counts.get(f"minecraft:{item}", counts.get(item, 0))
+        assert (have("diamond"), have("wheat"), have("torch")) == (0, 0, 5), counts
+        server.console("gamemode creative Alex")
+        time.sleep(1)
+        results["creative"] = alex.say("/sell all")
+        assert any("only with players in survival or adventure mode" in l for l in results["creative"]), results
+        server.console("gamemode survival Alex")
+        server.console("give Alex minecraft:diamond 10")
+        server.console("give Steve minecraft:emerald 5")
+        time.sleep(2)
+        results["trades"], steve = trades(server, alex, steve, port, ctl, resources, root)
+        results["coinflip"], alex_wins = coinflips(alex, steve)
+        results["lottery"], alex_lotto = lottery(alex, steve, alex_wins)
+        alex_after = 415 + (100 if alex_wins else -100) + (20 if alex_lotto else -30)
+        # Steve's 50 is still waiting: the server stops with both on.
+        lines = server.stop()
+        steve.quit()
+        alex.quit()
+        assert not any("panicked" in l for l in lines), lines[-40:]
+        economy = json.loads((data / "economy.json").read_text())
+        balances = {a["name"]: a["balance"] for a in economy["accounts"].values()}
+        results["economy.json"] = economy
+        held = sum(economy.get("held", {}).values())
+        assert balances["Alex"] == alex_after and sum(balances.values()) + held == 815, economy
+        audit = [json.loads(l) for l in (data / "audit.log").read_text().splitlines()]
+        results["audit"] = [a["kind"] for a in audit]
+        assert results["audit"] == ["open", "open", "eco_give", "pay", "sell 20 minecraft:wheat",
+                                    "sell 3 minecraft:diamond", "buy 5 minecraft:torch", "trade", "trade_failed",
+                                    "trade", "trade_money", "coinflip_stake", "coinflip_stake", "coinflip_win",
+                                    "coinflip_stake", "lottery_ticket", "lottery_ticket", "lottery_win"] + (
+                                    ["coinflip_cancel"] * (held == 0)), results["audit"]
+        swap = [a for a in audit if a["kind"] == "trade"][-1]
+        assert (swap["a_items"], swap["b_items"], swap["b_money"]) == (
+            [{"item": "minecraft:diamond", "count": 10, "plain": True}],
+            [{"item": "minecraft:emerald", "count": 5, "plain": True}], 35), swap
+        server.start()
+        alex = Client(ctl, resources, "Alex2", root)
+        alex.name = "Alex"
+        alex.join(port)
+        results["after_restart"] = alex.say("/balance")
+        assert any(f"Balance: {alex_after} coins" in l for l in results["after_restart"]), results
+        alex.quit()
+        server.stop()
+        economy = json.loads((data / "economy.json").read_text())
+        assert "held" not in economy and sum(a["balance"] for a in economy["accounts"].values()) == 815, economy
+        kinds = [json.loads(l)["kind"] for l in (data / "audit.log").read_text().splitlines()]
+        assert kinds[-1] in ("held_returned", "coinflip_cancel"), kinds[-3:]
+        results["stake_back"] = kinds[-1]
+        print(json.dumps({"proof": "smp", "ok": True, **results}, indent=2))
+    finally:
+        (out / "server.log").write_text("\n".join(server.lines))
+        for c in (alex, steve):
+            c.quit()
+        if server.__dict__.get("process") and server.process.poll() is None:
+            server.process.kill()
+        shutil.rmtree(root, ignore_errors=True)

native/smp/src/lib.rs

@@ -0,0 +1,15 @@
+//! The SMP's rules, as the bundle adds them to the game: each file is a
+//! module of `game` there and of this crate here, under the same name, so
+//! `super::smp_store` reaches the same code in both.
+#[path = "../mixins/smp/smp_economy.rs"]
+pub mod smp_economy;
+#[path = "../mixins/smp/smp_games.rs"]
+pub mod smp_games;
+#[path = "../mixins/smp/smp_lottery.rs"]
+pub mod smp_lottery;
+#[path = "../mixins/smp/smp_market.rs"]
+pub mod smp_market;
+#[path = "../mixins/smp/smp_store.rs"]
+pub mod smp_store;
+#[path = "../mixins/smp/smp_trade.rs"]
+pub mod smp_trade;