Project-M/CLAUDE.md

Project M — CLAUDE.md

Multiplayer game on Unity DOTS (Entities) + Netcode for Entities — server-authoritative, input-only clients, client prediction. This file is committed and is the authoritative, cross-machine source of conventions. The /dots-dev skill drives feature work; the one-time stack setup lives in Docs/dots-setup-task.md.

Stack — reverting to Unity 6.4.7 (stable) as of 2026-05-30

Package	Version	Notes
com.unity.entities	6.4.0	Entities/Collections/Graphics track the Editor version (6.x).
com.unity.entities.graphics	6.4.0	Renders entities under URP 17.4.
com.unity.collections	6.4.0	(transitive)
com.unity.netcode	1.13.2	Netcode for Entities (ECS). NOT com.unity.netcode.gameobjects. Independent 1.x line on Unity 6.4.
com.unity.physics	1.4.6	Unity Physics (DOTS). Independent 1.x line on Unity 6.4.
com.unity.transport	2.7.2	(transitive)
com.unity.burst	1.8.29	(transitive)
com.unity.mathematics	1.3.3	(transitive)

⚠️ The values above are the Unity 6.4.7 set being reverted to — verify against packages-lock.json after the editor downgrade re-resolves, and reconcile manifest.json if the brief 6.6 upgrade left explicit version pins.

Version history & status (2026-05-30): built on 6.4.7 (6000.4.7f1; Netcode 1.13.2 / Physics 1.4.6 / Entities 6.4.0). Briefly upgraded to 6.6.0a6, where Netcode→6.6.0, Physics→6.5.0, Entities→6.5.0 all renumbered into the editor line — BUT the alpha's Netcode/Transport runtime is broken (all in-editor connections fail with "invalid wrapped network interface"; confirmed engine bug via a zero-gameplay repro — see Docs/Vault DR-002 and Docs/UnityBugReport-Netcode-Transport-6.6.0a6.md). → Reverting to Unity 6.4.7 for stable netcode runtime. If returning to 6.6 later, expect the renumber and re-test the runtime. The M1 player slice should port to 6.4 / Netcode 1.13.2 with no or minimal changes — recompile and read_console after the downgrade.

Namespaces & assembly split

Root namespace: ProjectM. Code lives under Assets/_Project/Scripts/ in four asmdefs (never create/edit .csproj/.sln; only .asmdef):

Assembly	Namespace	Runs in	References
ProjectM.Simulation	ProjectM.Simulation	client + server worlds	Entities, Unity.Transforms, Collections, Mathematics, Burst, Unity.Physics, Unity.NetCode
ProjectM.Client	ProjectM.Client	client world only	+ Simulation, Unity.Entities.Graphics, Unity.InputSystem
ProjectM.Server	ProjectM.Server	server world only	+ Simulation, Unity.Transforms, Unity.NetCode
ProjectM.Authoring	ProjectM.Authoring	bake time (+ scene runtime)	Simulation, Entities, Unity.Entities.Hybrid, Collections, Mathematics, Unity.NetCode

• Simulation = components + systems shared by both worlds (most gameplay). Client/Server = world-specific. Authoring = …Authoring MonoBehaviours + Baker<T>.
• Other folders: Assets/_Project/Subscenes/ (baked entity subscenes), Assets/_Project/Prefabs/, Assets/_Project/Tests/EditMode/.

Build gotchas (learned — M1, 2026-05-30)

• Unity.Transforms must be a DIRECT asmdef reference for any assembly whose source-gen'd systems use LocalTransform/LocalToWorld. It is its own assembly; transitive visibility compiles your hand-written code but the Entities generator emits CS0246 inside the *.g.cs.
• Authoring asmdefs need Unity.Entities.Hybrid (defines Baker<T>) and Unity.Collections (baking source-gen). A nested baker class must not be named Baker (it shadows Baker<T> → CS0308/CS0246) — name it FooBaker.
• Never name an IComponentData PlayerInput, and don't using UnityEngine.InputSystem; in a file that references such a component: it collides with UnityEngine.InputSystem.PlayerInput, and the Entities generator binds RefRW<…> to the managed class → a misleading CS8377 "must be a non-nullable value type". Fully-qualify Input System types (UnityEngine.InputSystem.Keyboard.current) instead.
• IInputComponentData requires implementing FixedString512Bytes ToFixedString().
• An input-gather system that reads the managed Input System belongs in GhostInputSystemGroup as a non-Burst ISystem (or SystemBase), never inside the prediction loop.

Bootstrap & worlds

• ProjectM.Simulation.GameBootstrap : ClientServerBootstrap → overrides Initialize, sets AutoConnectPort = 7979 (in-editor auto-connect over IPC; set in M1 — was 0), calls CreateDefaultClientServerWorlds(). Entering Play Mode creates separate ServerWorld (WorldFlags.GameServer) and ClientWorld (WorldFlags.GameClient) — verified.
• Assets/_Project/Subscenes/Gameplay.unity is wired into SampleScene (GameObject GameplaySubScene) as a baking target. Replace SampleScene with a dedicated bootstrap scene when building for real.

DOTS / ECS conventions (authoritative summary)

Full rules: ~/.claude/skills/dots-dev/references/dots-conventions.md (Windows: %USERPROFILE%\.claude\skills\dots-dev\references\). These replace classic MonoBehaviour/GameObject patterns.

• struct : IComponentData is the default (unmanaged, Burst/job-friendly). class : IComponentData only for genuine managed refs (main-thread, no Burst). IBufferElementData for per-entity arrays. IEnableableComponent to toggle state without a structural change.
• Systems: ISystem (struct) + [BurstCompile] is the default; SystemBase only when touching managed objects. SystemAPI.Query<…>() to iterate. Aspects (IAspect) are DEPRECATED (Entities 1.4+) — do not author new ones. Entities.ForEach is legacy.
• Jobs: IJobEntity / IJobChunk; thread JobHandle through state.Dependency; mark inputs [ReadOnly]. Allocators: Temp (frame), TempJob (one job), Persistent (must dispose). Burst breaks on managed types/exceptions/reflection/strings.
• Structural changes (add/remove component, create/destroy entity) invalidate handles + cause sync points → batch via EntityCommandBuffer (Begin/EndSimulationEntityCommandBufferSystem; .AsParallelWriter() in parallel jobs).
• Baking: …Authoring MonoBehaviour + class FooBaker : Baker<FooAuthoring> → GetEntity(authoring, TransformUsageFlags.…) then AddComponent. Subscenes stream async — entities aren't present the instant a reference exists.
• Netcode: ghosts = replicated entities (GhostAuthoringComponent + [GhostField]); predicted (player-controlled, rolled back) vs interpolated. Core sim runs in PredictedSimulationSystemGroup (fixed step, runs multiple times per frame on rollback → must be deterministic/idempotent; filter with .WithAll<Simulate>()). Server-authoritative: clients send input (IInputComponentData), not state. RPCs (IRpcCommand) for one-off events. No wall-clock/Time.deltaTime/System.Random in predicted sim.
• Always verify volatile DOTS/Netcode API shape via context7 at code-time — do not trust memory. See context7-libraries.md. Pinned IDs for our versions: Entities → /websites/unity3d_packages_com_unity_entities_6_5_manual; Netcode → /websites/unity3d_packages_com_unity_netcode_1_10_api (closest published; we run 1.13.2 — re-resolve if a 1.13 set appears); ECS samples → /unity-technologies/entitycomponentsystemsamples.

Testing

• Default pattern = plain-Entities EditMode test: create a World, register the system in SimulationSystemGroup, tick, assert. Public API, always green, version-independent. Example: Assets/_Project/Tests/EditMode/HeartbeatSystemTests.cs. Run via Unity Test Runner or MCP run_tests(mode="EditMode", assembly_names=["ProjectM.Tests.EditMode"]).
• NetCodeTestWorld is internal in netcode 1.13.2 (Unity.NetCode.Tests, assembly Unity.NetCode.TestsUtils.Runtime.Tests), exposed only via a fixed [InternalsVisibleTo] allow-list of Unity assemblies. To use it you must name a test asmdef to match an entry (e.g. Unity.NetcodeSamples.EditModeTests) — or vendor the test utils. See Docs/Vault/07_Sessions/_Decisions/DR-001_Netcode_Test_Harness.md. This does not change on Unity 6.6. Netcode world boot is covered by the Play Mode check, not a NetCodeTestWorld test.
• Burst/source-gen errors surface at editor compile, not a plain build — always check read_console after script changes, and run a play/tick test, not just a compile.

Guardrails

• Never edit a .meta independently of its asset; delete an asset and its .meta together.
• Never read/write Library/, Temp/, obj/, Logs/, UserSettings/ (generated/cache). Use MCP resources for editor state instead.
• Never create/edit/commit .csproj/.sln — only .asmdef.
• No asset/scene edits during Play Mode. Check editor_state.advice.ready_for_tools before mutating; package adds/refreshes trigger domain reloads — wait for is_compiling=false.

Memory — four layers (which tool when)

Layer	Use for	Crosses machines?
In-repo vault Docs/Vault/	Design docs, decision records (DR-###), session logs, roadmap — human-facing truth	Yes (git)
basic-memory MCP	Semantic/wikilink recall over those same vault files	Yes (indexes the vault)
serena MCP	C# symbol nav (find_symbol, references) of Assets/_Project/	N/A (from code)
Native Claude memory (memory/, MEMORY.md)	Machine-local facts, working-style, preferences	No

• Where is X defined / who calls it → serena (fallback Grep/Glob). What did we decide / how does Z work → basic-memory → read the vault note. Literal string / asset GUID → Grep/Glob. Current DOTS API → context7. Conventions → this file.
• Cross-machine rule: durable truth goes in the vault or this file (both committed). Native memory/ is local-only and does NOT sync — never the sole home of a decision.
• serena C# caveat: its language server is flaky on Unity (can auto-install the wrong .NET, .sln load timeouts). If find_symbol errors/stalls, fall back to Glob/Grep (or add claude-context with local embeddings as a code-search index). serena live-verification was deferred at setup; confirm on first use.

Per-machine setup (NOT in git — redo on each machine)

.mcp.json is committed and portable (${CLAUDE_PROJECT_DIR} only). But each machine still needs:

1. uv/uvx, the Obsidian app + obsidian-cli, and the dots-dev skill in ~/.claude/skills/.
2. basic-memory project registration (machine-local config): uvx basic-memory project add gamevault "<repo>/Docs/Vault" --default, then uvx basic-memory reindex --full --search --embeddings --project gamevault.
3. Unity 6.4 opens the project and the CoplayDev Unity-MCP bridge connects (mcpforunity://editor/state → ready_for_tools).