Set up DOTS + Netcode for Entities foundation

One-time stack setup per Docs/dots-setup-task.md (Unity 6.4.7 / 6000.4.7f1).
Packages: entities 6.4.0, entities.graphics 6.4.0, netcode 1.13.2, physics 1.4.6.

- Assets/_Project asmdef split: ProjectM.Simulation/Client/Server/Authoring (root ns ProjectM)
- GameBootstrap : ClientServerBootstrap; verified separate client + server worlds in Play Mode
- Gameplay subscene wired into SampleScene as a baking target
- Heartbeat component + Burst ISystem; EditMode smoke test green (1/1)
- In-repo Obsidian vault (Docs/Vault) incl. DR-001 (plain-Entities test over internal NetCodeTestWorld)
- Portable .mcp.json (basic-memory + serena via ${CLAUDE_PROJECT_DIR}); CLAUDE.md conventions
- .gitignore for DOTS baking cache + machine-local config

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Docs/Vault/07_Sessions/_Decisions/DR-001_Netcode_Test_Harness.md

@@ -0,0 +1,26 @@
+---
+id: DR-001
+title: Netcode smoke/test harness approach
+status: accepted
+date: 2026-05-29
+tags:
+- decision
+- netcode
+- testing
+permalink: gamevault/07-sessions/decisions/dr-001-netcode-test-harness
+---
+
+# DR-001 — Test harness: plain-Entities over internal NetCodeTestWorld
+
+## Context
+
+Setup (`Docs/dots-setup-task.md` §4) called for a `NetCodeTestWorld` EditMode test. In **Netcode for Entities 1.13.2**, `Unity.NetCode.Tests.NetCodeTestWorld` (assembly `Unity.NetCode.TestsUtils.Runtime.Tests`) is **`internal`**, reachable only via a fixed `[InternalsVisibleTo]` allow-list of Unity's own assemblies. A consumer test can use it only by naming its test assembly to match an entry (e.g. `Unity.NetcodeSamples.EditModeTests`) — effectively impersonating a Unity sample assembly. Research (Unity ECS status, Dec 2025) shows no public consumer test harness on the roadmap, and that this is **unchanged by a Unity 6.6 upgrade** (Netcode stays independent 1.x; only Entities/Collections/Graphics renumber to the Editor version).
+
+## Decision
+
+Use a **plain-Entities EditMode test** as the default test pattern: create a `World`, register the system under test in `SimulationSystemGroup`, tick, assert. Public API only, no assembly-name impersonation, version-independent. Netcode **world boot** is verified separately by the §3 Play Mode check (`GameBootstrap` creates `ServerWorld` + `ClientWorld`).
+
+## Consequences
+
+- Clean, always-green tests with no fragile naming hacks.
+- Full client+server **connect+tick** coverage is not provided by this pattern. When needed (ghost/prediction work), revisit per-system: either name a dedicated test asmdef `Unity.NetcodeSamples.EditModeTests` to borrow the IVT grant, or vendor a copy of the netcode test utilities.