AGENTS.md and docs/architecture.md: a map of the code for agents

AGENTS.md (CLAUDE.md links to it): the crates and what each owns, how to build and test fast, where each subsystem of horizon-client lives, how Game is organised, the two single-player paths and how to test both, the vanilla reference, and the rules that bite. docs/architecture.md: feature -> files -> checks for the 40 areas changed most in the last 30 days. Co-Authored-By: Claude Opus 5.5 <[email protected]>
2026-11-07 02:56:17 -10:00 · 2026-10-23 16:18:44 +02:00
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+# Horizon: a map for agents
+
+Minecraft: Java Edition 26.3 rewritten in Rust (wgpu). Vanilla is the specification wherever it has the
+feature. Read [CONTRIBUTING.md](CONTRIBUTING.md) once; this page tells you where things are.
+Feature → files → harness for the most-changed areas: [docs/architecture.md](docs/architecture.md).
+
+## Rules that bite
+
+- **Never commit Mojang's files**: game jars, assets, decompiled source, prepared resources (`.local/`).
+  `tools/check_public_tree.py` rejects them; `git config core.hooksPath .githooks` runs it on commit.
+- **Keep your runs away from real player data.** Any game or launcher you start gets fresh `mktemp -d`
+  folders in `HORIZON_HOME` (the game's data), `HORIZON_LAUNCHER_HOME`, `XDG_DATA_HOME` and
+  `XDG_CONFIG_HOME`, plus `HORIZON_LAUNCHER_NO_SELF_UPDATE=1` and `HORIZON_NO_AUDIO=1`. Never write to
+  `~/.local/share/{applications,horizon,horizon-launcher}` or `~/.local/bin`.
+- **Mark what an agent posts.** A PR body starts with
+  `> 🤖 Opened by Ludovic's AI agent (Claude), not by Ludovic himself.` (issues: "Filed by", reviews:
+  "Review by"); every comment starts with `🤖 Agent:`. Never write as Ludovic.
+- **Attribution.** Commits end with `Co-Authored-By: Claude <model> <[email protected]>`; PR bodies end
+  with `🤖 Generated with [Claude Code](https://claude.com/claude-code)`.
+- Everything players run is Rust. Python/Java only for dev tools and harness drivers in `tools/`.
+- Horizon-only features follow [docs/design-system.md](docs/design-system.md) and are off by default where
+  they would change the vanilla look.
+- Small PRs (< ~500 lines). Labels: `feature` (players get something new), `skip-release` (they see no
+  change), none for a fix, `release-now` for crash fixes. Every merge to main ships
+  ([docs/release-flow.md](docs/release-flow.md)).
+- Contributors first: `gh pr list --state open --search <area>` before you start; never duplicate theirs.
+
+## Crates
+
+Game workspace (root `Cargo.toml`); `launcher/` and `crates/horizon-telemetry-server` are separate workspaces.
+
+| Crate | Owns |
+|---|---|
+| `horizon-client` | The game: a lib (`src/lib.rs`, ~190 flat modules) and the bin (`src/main.rs` → `game.rs` + `game/`), plus `horizon-ctl` (`src/bin/horizon-ctl/`). Also the dedicated server (`--dedicated`) |
+| `horizon-world` | Vanilla world data with no gameplay loop: NBT, regions, chunks, `datafix/`, `worldgen/`, `level/` (server-side block behaviour, ticks, redstone), entity physics, items, effects, food, damage |
+| `horizon-core` | Simulation primitives: Java `Random`s, `jmath` (HotSpot-exact `Math`), positions, noise, density, paletted storage, `version.rs` (the pinned version) |
+| `horizon-protocol` | Network protocol 777: codecs, framing, encryption, `packets/{handshake,status,login,configuration,play}.rs`, `entity_data.rs` |
+| `horizon-assets` | Resource decoding: block-state and item models, baking, atlases |
+| `horizon-prepare` | Builds `.local/horizon-client/26.3` from the player's own Minecraft install (runs the Java exporters) |
+| `horizon-server` | `horizon-server`: `server.toml`, CLI, supervisor of the headless game ([docs/hosting.md](docs/hosting.md)) |
+| `horizon-server-files` | `server.properties`, eula, ops/whitelist/bans, usercache |
+| `horizon-friends`, `horizon-relay` | Play with Friends: invite codes, encrypted tunnel, the relay ([docs/play-with-friends.md](docs/play-with-friends.md)) |
+| `horizon-shaderpack` | OptiFine/Iris packs: preprocessor, GLSL → WGSL ([docs/shader-packs.md](docs/shader-packs.md)) |
+| `horizon-mods`, `horizon-mod-sdk`, `cargo-horizon-mod` | Sandboxed WebAssembly mods: runtime, SDK + WIT, `cargo horizon-mod` ([docs/mods.md](docs/mods.md)) |
+| `horizon-port-pack` | Porting Java modpacks ([docs/modpacks.md](docs/modpacks.md)) |
+| `horizon-theme` | Design tokens and fonts for the launcher, the game's own menus and the website |
+| `horizon-telemetry`, `horizon-telemetry-server`, `horizon-bench` | Opt-in data collection, its ingest server, the benchmark report format |
+| `horizon-dualsense`, `horizon-threads`, `horizon-release-sign`, `horizon-bots`, `voxel-kernels`, `xtask` | DualSense output, thread priorities, signed release checksums, load-test bots, occupancy kernels, repo tasks |
+| `launcher/` | GPUI launcher: `main.rs` (UI), `backend.rs` (installs, updates), `cli.rs`, `mcp.rs`, `*_page.rs` |
+
+Other top-level folders: `tools/` (harnesses and dev scripts), `tests/` (Python unit tests: `python3 -m
+unittest discover -s tests`), `mods/horizon/src/test/java/dev/horizonlab/parity/` (Java oracles),
+`website/` (playhorizon.dev; its paths are relative to `website/`), `docs/`, `.github/workflows/`.
+
+## Build and test fast
+
+```sh
+python3 tools/pr_ready.py                  # the self-check: fmt, clippy -D warnings, touched crates' tests, harnesses; paste its block in the PR
+python3 tools/pr_ready.py --quick          # same without harnesses
+cargo test -p horizon-client --lib --bins --tests   # skips the 104 examples (pr_ready does this); `--doc` separately
+cargo build --profile fast -p horizon-client        # optimized, quick to link: use it to play or run lan_e2e
+python3 tools/parity.py --changed origin/main       # the harnesses your branch can affect (CI's parity job)
+python3 tools/parity.py --changed-files paths.txt --list   # which harnesses cover these files, without running them
+python3 tools/parity.py mob_ai sculk       # named harnesses
+python3 tools/lan_e2e.py --check chest     # two real games over LAN (host in-frame); --server-thread for the host on its server thread
+python3 tools/agent_control_e2e.py         # horizon-ctl / MCP end to end
+```
+
+- Harnesses and the game need the vanilla data in `.local/` (`minecraft/`, `horizon-client/26.3`, `datagen/`,
+  `tools/`): see [docs/parity-workflow.md](docs/parity-workflow.md). Without it, pr_ready lists the
+  harnesses for CI.
+- A harness = `tools/test_<name>_parity.py` (324 of them) + a Java oracle (`mods/horizon/src/test/java/dev/horizonlab/parity/Vanilla*Oracle.java`)
+  + a Rust probe: `crates/<crate>/examples/<name>_{probe,fixture}.rs` (horizon-world 175, horizon-client 104),
+  or the game binary with a fixture env var (`game/dispense_fixture.rs`, `game/sculk_fixture.rs`,
+  `game/command_harness.rs`, `game/net_harness.rs`). Copy a nearby harness for a new one.
+- Probes build into `.local/parity-target/`; harnesses find binaries via `lab.cargo_target()`, never `target/`.
+- What a change reruns (of 329 harnesses, measured 2026-10-23): a file of the game binary (`game.rs`, `game/`)
+  ~25, a file of the client lib ~103, of `horizon-world` ~103–109, of `horizon-core` ~119. Plan for it.
+- Rust integration tests: `crates/horizon-client/tests/` (`lan_bot.rs`, `generation_saves.rs`, `streaming_meshes.rs`).
+- **macOS:** `cargo build/test --workspace` may fail to link the two wasm guest cdylibs (undefined
+  `horizon:mods/events` symbols) until #1446 lands: add `--exclude coords-hud --exclude horizon-mods-test-guest`.
+  Their real check is `cargo test -p horizon-mods` (builds them for `wasm32-unknown-unknown`).
+- Linux needs `libasound2-dev libudev-dev`; `--no-default-features` drops audio and controllers (the server build).
+- Run and drive the game (starts the `horizon-client` beside `horizon-ctl`; other arguments go to the game):
+  `target/fast/horizon-ctl --socket $PWD/ctl.sock launch --world W --creative --offscreen --wait --resources $PWD/.local/horizon-client/26.3`,
+  then `horizon-ctl --socket … state|keys|turn|command|screenshot|quit`
+  ([docs/horizon-ctl-commands.md](docs/horizon-ctl-commands.md)).
+
+## Vanilla reference
+
+- Decompiled sources: `.local/minecraft/26.3/sources/{client,server}/` (`python3 tools/lab.py decompile`).
+- Bytecode queries (callers through lambdas, every overload):
+  `python3 tools/rea_vanilla.py method net.minecraft.world.level.block.DispenserBlock dispenseFrom`
+  ([docs/decompilation-status.md](docs/decompilation-status.md)).
+- A harness runs the oracle against the real 26.3 jars and the Rust probe on the same inputs, then compares
+  their JSON. Oracle runs are cached by `tools/parity_shim.py`; `--fresh` reruns them.
+- Mirror vanilla's `Math` calls with `horizon_core::jmath`, and vanilla's RNG with `horizon_core::random`:
+  random draws must happen in vanilla's order.
+
+## horizon-client: where things live
+
+`L:` = lib (`crates/horizon-client/src/`), `G:` = bin (`crates/horizon-client/src/game/`). The lib can't see
+`Game`; bin code reaches the lib as `horizon_client::<module>`.
+
+| Subsystem | Files |
+|---|---|
+| Game loop, tick, frame | `game.rs`: `fn run`, `impl ApplicationHandler for Game` (`window_event`, `about_to_wait`), `fn tick`, `fn tick_world`, `fn render`; L: `clock.rs`, `window.rs`, `spans.rs` |
+| Rendering | L: `gfx.rs` (`Renderer::new`, `Renderer::render`), `gfx/` (cull, occlusion, translucency, upload, timing, lod, weather, stars, end_sky), `*.wgsl`, `particles.rs`, `block_entity_render.rs`, `item_render.rs`, `fog.rs`, `clouds.rs`, `camera.rs`, `first_person.rs`; G: `render_tick.rs`, `item_draw.rs` |
+| Chunks, streaming, light | L: `streaming.rs` (worker pool: generate, light, mesh), `world.rs`, `chunk.rs`, `chunk_map.rs`, `light.rs`, `mesher.rs` + `mesher/`, `vanillagen.rs` (binds horizon-world's generator), `lod.rs` + `lod/`, `ticket_levels.rs`; G: `world_loading.rs`, `postprocess.rs`; game.rs `fn update_world` |
+| World generation | `crates/horizon-world/src/worldgen/` (`generator*.rs`, `feature_graph.rs`, `structure/`, `carver/`) |
+| Block behaviour | `crates/horizon-world/src/level/` (`mod.rs`, `tick.rs`, `hooks.rs`, `redstone.rs`, `place.rs`, `interact.rs`); game.rs `fn tick_blocks`, `fn process_level_events` |
+| Mobs | L: `mobs.rs` (types), `mobs/` (`ai.rs`, `goals.rs`, `brain.rs`, `*_brain.rs`, `nav.rs`, `path.rs`, `species.rs`, `spawning.rs`, `render.rs`, `anim.rs`); G: `creatures.rs` (ticking, spawning, mob events), one file per mob family (`dragon.rs`, `wither.rs`, `villagers.rs`, `piglins.rs`, `golems.rs`...), `natural_spawning.rs` |
+| Other entities | L: `entities.rs`, `projectiles.rs`, `arrows.rs`; G: `boats.rs`, `minecarts.rs`, `mounts.rs`, `armor_stands.rs`, `paintings.rs`, `frames.rs`, `fireworks.rs`, `tnt.rs`, `explosion.rs` |
+| Player actions | game.rs (`fn use_hand`, `fn use_item`, `fn attack`, `fn tick_mining`, `fn break_block`); G: `hand.rs`, `combat.rs`, `consume.rs`, `potions.rs`, `shield.rs`, `crossbow.rs`, `trident.rs`, `fishing.rs`; L: `motion.rs` + `motion/` (movement), `collisions.rs`, `items.rs`, `item_data.rs` |
+| Inventory and containers | L: `menu.rs` (`AbstractContainerMenu.clicked`), `container_screen.rs`, `containers.rs`, `creative.rs`, `crafting.rs`, `recipe_book*.rs`, `stations.rs`, `merchant.rs`; game.rs `fn menu_ops`, `fn click_inventory`; G: `stations.rs`, `trading.rs`, `recipe_book.rs`, `machines.rs` |
+| Commands | parse: L: `command/` (`args.rs`, `selector.rs`, `tree_*.rs`, `vanilla.rs`); run: G: `commands.rs` (dispatch) + `commands/*.rs` (`admin`, `execute`, `items`, `players`, `world_cmds`...); L: `scoreboard_cmd.rs`, `data_cmd.rs`, `nbt_path.rs`; G: `functions.rs`, `command_blocks.rs` |
+| UI screens | `Screen` enum in game.rs; L: `title.rs` + `title/`, `options_ui.rs`, `multiplayer.rs`, `pack_screen.rs`, `graphics_ui.rs`, `screen_draw.rs`, `ui.rs` (widgets), `hud.rs`, `hud_layout.rs`, `hud_overlays.rs`, `chat.rs`, `tab_list.rs`; G: `startup_menu.rs`, `screens.rs` (pause, death), `options.rs`, `lan_screen.rs`, `chat.rs`, `sign_edit.rs`, `books.rs` |
+| Multiplayer client | L: `net.rs` (network thread); G: `remote.rs` (`fn handle_packet`, `fn tick_remote`), `remote_*.rs` (mob data, objects, projectiles, vehicles, stations) |
+| LAN host / server side | L: `lan/` (`conn.rs` handshake + login threads, `hub.rs` + `hub/` play state, `chunks.rs`, `entity.rs`, `tracking.rs`, `guest.rs`, `playerdata.rs`); G: `lan.rs` (`LanHost`), `lan_actions.rs` (`fn as_guest`, `fn tick_guests`), `lan_*.rs` per feature, `lan_entities.rs` (tracked entities) |
+| Integrated server | G: `integrated.rs` (the server thread), `levels.rs` (one level per dimension, `fn tick_server`), `server_travel.rs` |
+| Dedicated server | G: `dedicated.rs`, `dedicated/status.rs`; crates `horizon-server-files`, `horizon-server` |
+| Save and load | L: `save.rs` (level.dat, regions, playerdata), `entity_nbt.rs`, `block_entity_nbt.rs`, `options_file.rs`; G: `saving.rs`, `persist.rs` (entities); `crates/horizon-world/src/{region.rs,nbt.rs,datafix/}` |
+| Input | game.rs `fn window_event`, `fn key_pressed`, `fn play_mouse`; L: `keybinds.rs`, `keymapping.rs`, `key_names.rs`, `mouse.rs`, `input.rs`, `interaction_input.rs`, `gamepad.rs`, `osk.rs`, `clipboard.rs`; G: `pad.rs`, `pad_menu.rs` |
+| Audio | L: `audio.rs` (mixer), `sound_engine.rs`, `sound_events.rs`, `music.rs`, `ambience.rs`; G: `music.rs`, `subtitle_hud.rs` |
+| Resource packs | L: `packs.rs` + `packs/`, `pack_screen.rs`, `atlas_sources.rs`, `sprites.rs`, `mipmap.rs`, `model_library.rs`, `font.rs`, `lang.rs`; crate `horizon-assets`; G: `packs.rs` |
+| Shader packs | L: `shader_pack.rs` (Horizon WGSL packs), `java_pack.rs` + crate `horizon-shaderpack` (Iris/OptiFine), `gfx/pack_stages.rs`, `gfx/java_stages.rs`; G: `shader_packs.rs` |
+| Agent control | L: `control.rs` (socket), `bin/horizon-ctl/`; G: `control.rs`, `agent.rs`, `events.rs`, `ui_control.rs` ([docs/agent-control.md](docs/agent-control.md)) |
+| Mods | crate `horizon-mods`; G: `mods.rs`; L: `mod_content.rs`, `mod_list.rs` |
+| Horizon extras, settings | L: `extras.rs`, `graphics.rs`, `settings.rs`, `minimap.rs`; G: `extras.rs`, `tweaks.rs`, `options.rs` |
+
+## How `Game` is organised
+
+- `struct Game` (game.rs, ~290 fields) holds everything. Its methods are spread over ~180 files: game.rs keeps
+  the core (tick, render, input, inventory, world open/close) and each `game/<feature>.rs` adds an
+  `impl Game<'_>` block for one feature, with its own state types. Fields are private to the bin.
+- Find a feature's code: `grep -rn "fn tick_<thing>\|fn <verb>_<thing>" crates/horizon-client/src/game*`;
+  the file is usually `game/<thing>s.rs`. Who calls it: grep the name in game.rs's `fn tick` / `fn tick_world`.
+- Fields that say which mode runs: `remote` (this window is a client of a server: multiplayer, LAN guest, or
+  single player on its server thread), `lan` (`LanHost`: this world is open to the network), `integrated`
+  (the window's own server thread), `serving` (this `Game` *is* that server thread), `options.dedicated`.
+  `fn tick` returns `tick_remote()` when `remote` is set; nothing else of the local simulation runs.
+- A server's players run through the same gameplay code as the local player: `as_guest` swaps the guest's
+  state (position, inventory, mode, mining, item use) into `Game` for one call (`game/lan_actions.rs`), and
+  `levels.rs` swaps whole dimensions in the same way. Changes reach clients through the block log, level
+  events and the entity tracker (`lan/tracking.rs`, `game/lan_entities.rs`).
+- Shared read-only data: `Resources` (`res`: blocks, items, recipes, mob types, biomes) and `PackResources`
+  (`pack`), both in game.rs.
+
+## The two single-player paths
+
+1. **In-frame (default since #1428):** the window's `Game` ticks the world itself, one level that follows
+   the player (`fn enter_dimension`). This is what Stable players run and what harnesses test.
+2. **Server thread (`--server-thread` or `HORIZON_SERVER_THREAD=1`):** `game/integrated.rs` runs a second
+   `Game` (`serving`) on a "Server thread" with one level per dimension; the window joins it as a client
+   through memory (`remote`), exactly as a LAN guest or a dedicated server's player does. Not at parity yet:
+   open `[server-thread]` issues list the gaps.
+
+LAN guests and dedicated servers always use the server code, so a fix there serves both. Test both paths
+when you touch player-facing gameplay:
+
+```sh
+cargo run --profile fast -p horizon-client -- --resources .local/horizon-client/26.3 --world T                   # in-frame
+cargo run --profile fast -p horizon-client -- --resources .local/horizon-client/26.3 --world T --server-thread   # server thread
+python3 tools/lan_e2e.py --check <name>                  # host in-frame, guest is a server client
+python3 tools/lan_e2e.py --server-thread --check <name>  # host on its server thread (portals, levels, distance, lava need it)
+python3 tools/parity.py dedicated_server server_entities server_player_damage
+```
+
+## Docs worth knowing
+
+[docs/parity-workflow.md](docs/parity-workflow.md) (runner, gate, shards, scopes) ·
+[docs/native-client.md](docs/native-client.md) (options, controls, horizon-ctl) ·
+[docs/server-levels.md](docs/server-levels.md) (levels per dimension) ·
+[docs/rust-parity.md](docs/rust-parity.md) (what is ported) · [docs/known-issues.md](docs/known-issues.md) ·
+[docs/release-flow.md](docs/release-flow.md) · [docs/README.md](docs/README.md) (index).
@@ -0,0 +1 @@
+AGENTS.md
@@ -4,6 +4,7 @@ To play, use [the launcher](../launcher/README.md); the project site is [playhor

 ## Build and run

+- [AGENTS.md](../AGENTS.md) and [Architecture](architecture.md): where each part of the code lives, how `Game` is organised, which harness checks which area.
 - [Build from source](../README.md#build-from-source): your own copy of the game, resource preparation, `cargo run`.
 - [Native client](native-client.md): options, controls, the dedicated server, `horizon-ctl` scripting, packaging, architecture.
 - [Host a server](hosting.md): install `horizon-server`, prepare the game files, first run, `server.toml`, the commands, the web panel, backups, services and Docker; what works today and what doesn't yet.
@@ -0,0 +1,57 @@
+# Architecture: feature → files → checks
+
+The 40 areas changed most often in the 30 days to 2026-10-23 (commits on main touching the area; `game.rs` is
+counted only for the game loop because nearly every gameplay change touches it). The crate map, how `Game` is
+organised and how to build and test are in [AGENTS.md](../AGENTS.md).
+
+Paths: `L/` = `crates/horizon-client/src/`, `G/` = `crates/horizon-client/src/game/`, `W/` =
+`crates/horizon-world/src/`. Checks: a bare name is a harness (`python3 tools/parity.py <name>`, script
+`tools/test_<name>_parity.py`); `lan_e2e <check>` is `python3 tools/lan_e2e.py --check <check>`.
+
+For the full set of harnesses a file can affect, ask the runner:
+`printf '%s\n' <paths> > /tmp/p.txt && python3 tools/parity.py --changed-files /tmp/p.txt --list`.
+Any file of the game binary (`game.rs`, `game/`) selects the ~25 harnesses that run the binary; a client lib
+file selects ~103.
+
+| # | Area (commits) | Files | Checks |
+|---|---|---|---|
+| 1 | Game loop, tick order, frame pacing (554) | `L/game.rs` (`fn tick`, `fn tick_world`, `fn render`, `about_to_wait`), `L/clock.rs`, `L/window.rs`, `L/spans.rs` | game_loop, frame_limiter, interaction_input, tick |
+| 2 | Mobs in the game loop, spawning (166) | `G/creatures.rs`, `G/natural_spawning.rs`, `L/mobs/spawning.rs`, `L/mobs/spawn_rules.rs`, `L/mobs/spawn_selection.rs`, `L/mobs/finalize.rs`, `G/spawner.rs`, `G/trial_spawner.rs` | natural_spawn, spawn_rules, finalize_spawn, spawner, trial_spawner, mob_ai |
+| 3 | World save and load (163) | `L/save.rs`, `G/saving.rs`, `G/persist.rs` (entities), `L/entity_nbt.rs`, `L/block_entity_nbt.rs`, `W/region.rs`, `W/nbt.rs` | save_roundtrip, world_reopen, world, datafix |
+| 4 | World generation (153) | `W/worldgen.rs`, `W/worldgen/` (`generator*.rs`, `feature_graph.rs`, `structure/`, `placement/`), `L/vanillagen.rs` | chunk_generation, worldgen, server_world_gen, world_spawn, feature_graph, feature_placement, decoration and the other worldgen harnesses |
+| 5 | Multiplayer client, packets in (145) | `G/remote.rs` (`fn handle_packet`, `fn tick_remote`), `G/remote_*.rs`, `L/net.rs` | dedicated_server, server_entities, lan_e2e (all) |
+| 6 | Agent control, horizon-ctl (145) | `L/control.rs`, `L/bin/horizon-ctl/`, `G/control.rs`, `G/agent.rs`, `G/events.rs`, `G/ui_control.rs` | `python3 tools/agent_control_e2e.py`; `cargo test -p horizon-client --bin horizon-ctl` |
+| 7 | CI and release (134) | `.github/workflows/` (`ci.yml`, `parity.yml`, `release.yml`, `launcher.yml`), `tools/ci/`, `tools/parity.py`, `tools/pr_ready.py` | `python3 -m unittest discover -s tests`; actionlint (`.github/actionlint.yaml`) |
+| 8 | LAN host: connections, play state, tracking (133) | `L/lan/` (`conn.rs`, `hub.rs` + `hub/`, `chunks.rs`, `entity.rs`, `tracking.rs`, `guest.rs`, `playerdata.rs`), `G/lan.rs` | lan, lan_e2e (all), `cargo test -p horizon-client --test lan_bot` |
+| 9 | Renderer core (132) | `L/gfx.rs` (`Renderer::new`, `Renderer::render`), `L/gfx/` (cull, occlusion, translucency, upload, timing, lod) | client_graphics, culling_rays, translucency; `horizon-client --benchmark standard` |
+| 10 | Launcher (124) | `launcher/src/` (`main.rs`, `backend.rs`, `cli.rs`, `mcp.rs`, `servers_page.rs`) | `cd launcher && cargo test`; `python3 tools/launcher_mcp_e2e.py` |
+| 11 | Mob types and species (117) | `L/mobs.rs`, `L/mobs/species.rs`, `L/mobs/data.rs`, `L/mobs/living.rs`, `L/mobs/drops.rs`, `L/mobs/gear.rs` | mob_attributes, entity_attribute, entity_death_loot, mob_ai |
+| 12 | Guests' actions on a server (98) | `G/lan_actions.rs` (`fn as_guest`, `fn tick_guests`), `G/lan_{attributes,pvp,chat,crafting,stations,trading,mount_menu,waypoints}.rs` | server_player_combat, server_player_damage, server_player_targets, lan_e2e (all) |
+| 13 | Modpack porting, mod content (97) | `crates/horizon-port-pack/`, `L/mod_content.rs`, `tools/port_*.py`, `packs/` | `cargo test -p horizon-port-pack`; `python3 tools/mod_port_harness.py` |
+| 14 | Mob AI (96) | `L/mobs/ai.rs`, `goals.rs`, `brain.rs`, `*_brain.rs`, `nav.rs`, `path.rs`, `control.rs` | mob_ai (probe `examples/mob_ai_probe.rs`; known failure on main: drowned_*, #290) |
+| 15 | Items and item use (96) | `L/items.rs`, `L/item_data.rs`, `G/hand.rs`, `G/consume.rs`, `G/potions.rs`, `L/effects.rs`; game.rs `fn use_hand`, `fn use_item` | use_item_on, item_use, item_use_lifecycle, consumable, consume_effect, status_effect |
+| 16 | Options and settings screens (93) | `L/options_ui.rs`, `G/options.rs`, `L/settings.rs`, `L/options_file.rs`, `L/graphics_ui.rs`, `L/graphics.rs` | options, toggle_keys |
+| 17 | HUD, chat, tab list (93) | `L/hud.rs`, `L/hud_layout.rs`, `L/hud_overlays.rs`, `L/chat.rs`, `G/chat.rs`, `L/tab_list.rs`, `L/locator_bar.rs`, `G/locator_bar.rs` | hud, tab_list, locator_bar, chat_screen, secure_chat |
+| 18 | Command execution (88) | `G/commands.rs`, `G/commands/*.rs`, `L/scoreboard_cmd.rs`, `L/data_cmd.rs`, `G/functions.rs` | command_exec (corpus `tools/command_exec_corpus.py`), scoreboard, server_ops_feedback, lan_e2e commands |
+| 19 | Chunk streaming, light, tickets (85) | `L/streaming.rs`, `L/world.rs`, `L/chunk.rs`, `L/chunk_map.rs`, `L/light.rs`, `L/ticket_levels.rs`, `L/tick_chunk_membership.rs`, `G/world_loading.rs` | light, chunk_status, random_tick_sections; `cargo test -p horizon-client --test streaming_meshes` |
+| 20 | Mob models and animation (78) | `L/mobs/render.rs`, `L/mobs/anim.rs`, `L/mobs/body_anim.rs`, `L/mobs/keyframes.rs`, `L/entity.wgsl` | entity_model |
+| 21 | Block behaviour, server side (78) | `W/level/` (`mod.rs`, `tick.rs`, `hooks.rs`, `data.rs`, `redstone.rs`, `place.rs`), `G/block_entity_ticks.rs`, `G/moving_pistons.rs` | block_update, redstone, random_tick, simple_block, piston_movement, block_entity_tickers |
+| 22 | Player movement and collision (75) | `L/motion.rs` + `L/motion/`, `L/collisions.rs`, `W/entity_move.rs`, `W/player_travel.rs`, `W/collision.rs` | collision, entity_move, player_travel, living_motion, climbing, swimming; `python3 tools/test_native_scene_motion.py` |
+| 23 | Resource packs and models (65) | `L/packs.rs` + `L/packs/`, `L/pack_screen.rs`, `L/atlas_sources.rs`, `L/sprites.rs`, `L/model_library.rs`, `G/packs.rs`, `crates/horizon-assets/` | resource_pack, pack_selection, pack_screen, model_resolution, item_model, mipmap |
+| 24 | Container menus and inventory (61) | `L/menu.rs`, `L/container_screen.rs`, `L/containers.rs`, `L/creative.rs`; game.rs `fn menu_ops`, `fn click_inventory` | menu_click, container_screen, creative, lan_e2e containers clicks |
+| 25 | Workstations (60) | `L/stations.rs`, `G/stations.rs`, `L/enchant.rs`, `L/brewing.rs` | enchanting, screen_layout, lan_e2e brewing loom stonecutter grindstone anvil smithing |
+| 26 | Crafting and the recipe book (59) | `L/crafting.rs`, `L/recipe_book.rs`, `L/recipe_book_screen.rs`, `G/recipe_book.rs`, `G/machines.rs`, `G/machines/crafter.rs` | recipe, recipe_book, recipe_book_view, place_recipe, ghost_recipe, crafter |
+| 27 | Vehicles and mounts (54) | `G/boats.rs`, `G/minecarts.rs`, `G/mounts.rs`, `G/mount_menu.rs`, `G/llamas.rs`, `G/passengers.rs` | server_entities, lan_e2e boats minecarts riding mounts |
+| 28 | Villagers, trading, raids (50) | `L/mobs/villager*.rs`, `L/merchant.rs`, `G/trading.rs`, `G/villagers.rs`, `L/raid.rs`, `G/raids.rs`, `L/gossip.rs` | trading, raid, mob_ai |
+| 29 | Title, worlds, startup (49) | `L/title.rs` + `L/title/`, `G/startup_menu.rs`, `L/title_edition.rs` | world_options; `cargo test -p horizon-client --lib title` |
+| 30 | Dedicated server, horizon-server (48) | `G/dedicated.rs`, `G/dedicated/status.rs`, `crates/horizon-server/`, `crates/horizon-server-files/` | dedicated_server, server_files, user_cache, online_mode, server_ops_feedback |
+| 31 | Particles and client effects (46) | `L/particles.rs`, `G/render_tick.rs`, `G/level_particles.rs`, `L/animate_tick.rs` | particle_providers, block_particles, entity_particles, emitter_particles, marker_particles |
+| 32 | Bosses and the End (45) | `G/dragon.rs`, `G/wither.rs`, `G/end.rs` | server_dragon, end_podium, end_gateway |
+| 33 | Protocol and packets (44) | `crates/horizon-protocol/src/` (`packets/play.rs`, `entity_data.rs`, `connection.rs`) | dedicated_server, online_mode, secure_chat; `cargo test -p horizon-protocol` |
+| 34 | Multiplayer and LAN screens, friends (44) | `L/multiplayer.rs`, `G/lan_screen.rs`, `G/friends.rs`, `L/friends_screen.rs`, `crates/horizon-friends/`, `crates/horizon-relay/` | lan, world_options; `python3 tools/test_friends.py` |
+| 35 | Dispensers (43) | `G/dispenser.rs`, `G/dispense_fixture.rs` (the harness side) | dispenser |
+| 36 | Audio and music (38) | `L/audio.rs`, `L/sound_engine.rs`, `L/sound_events.rs`, `L/music.rs`, `G/music.rs`, `L/ambience.rs`, `G/subtitle_hud.rs` | sound_engine, sound_event, music, situational_music, ambient_sound, subtitle |
+| 37 | Integrated server and levels (34) | `G/integrated.rs`, `G/levels.rs`, `G/server_travel.rs` | server_dimension_players, `lan_e2e --server-thread` (portals, levels, distance, lava) |
+| 38 | Command parsing (34) | `L/command/` (`args.rs`, `selector.rs`, `tree_*.rs`, `vanilla.rs`) | command_parse (corpus `tools/command_parse_corpus.py`) |
+| 39 | Benchmarks and telemetry (34) | `L/benchmark.rs`, `tools/perf_bench.py`, `L/telemetry.rs`, `crates/horizon-telemetry*/`, `crates/horizon-bench/` | `python3 -m unittest tests.test_perf_bench`; [benchmark.md](benchmark.md) |
+| 40 | Explosions and TNT (31) | `G/explosion.rs`, `G/tnt.rs` | lan_e2e blast; no dedicated harness yet |