# Arch render-scene dependency decision

**Date:** 2026-07-24

**Scope:** Modern Runtime Slice F1 only

## Decision

Pin `Arch` version `2.1.0` directly in `AcDream.App`. Do not reference it from
Core, UI abstractions, plugins, or any other production project. Do not use
Arch systems, command buffers, parallel queries, jobs, events, source
generators, persistence, relationships, or extension packages.

The only allowed Arch namespace is:

```text
src/AcDream.App/Rendering/Scene/Arch/
```

Everything outside that folder uses acdream-owned `IRenderScene`, wrapper
identities, packed component values, deltas, borrowed queries, digests, and
memory-accounting values. Arch entities and primitive wrapper values cannot
cross that boundary.

## Verification

- Official package: [NuGet `Arch 2.1.0`](https://www.nuget.org/packages/Arch/2.1.0)
- Official source/tag:
  [genaray/Arch `v2.1.0`](https://github.com/genaray/Arch/tree/v2.1.0)
- License:
  [Apache License 2.0](https://github.com/genaray/Arch/blob/v2.1.0/LICENSE.MD)
- Selected source tag commit:
  `04d52e7268eb6f376ca4841a0c204334120c5e9d`

The selected package supplies .NET 6 and .NET Standard 2.1 assets, both
compatible with acdream's .NET 10 App target. The v2.1.0 source was inspected
for the exact API used by the adapter:

- `World.Create`
- generic `World.Create<T...>`
- `World.Set<T>` / `World.Get<T>`
- `World.Destroy(Entity)` / `World.Destroy(World)`
- `World.Size`, `World.Capacity`, and `World.Archetypes`
- archetype chunk count and chunk-size accounting

The resolved dependency graph was captured with
`dotnet list package --include-transitive`. It resolves:

```text
Arch                         2.1.0
Arch.LowLevel                1.1.5
Collections.Pooled           2.0.0-preview.27
CommunityToolkit.HighPerformance 8.4.0
Microsoft.Extensions.ObjectPool  7.0.0
ZeroAllocJobScheduler        1.1.2
```

No package in the resolved App graph was reported vulnerable by NuGet's
`--vulnerable --include-transitive` audit on 2026-07-24. The transitive job
scheduler is not initialized or called by acdream; Slice F uses only
single-threaded structural operations and direct component access on the
existing update thread.

## Containment proof

`RenderSceneArchitectureTests` enforces all of the following:

1. `Arch` is a direct package reference in `AcDream.App` only.
2. Arch namespaces occur only in the contained adapter folder.
3. Reflection finds no Arch field, property, parameter, or return type outside
   that namespace.
4. Raw wrapper identity extraction occurs only in the adapter (apart from the
   private contract declarations themselves).

This is storage selection, not simulation architecture. `LiveEntityRuntime`,
`GpuWorldState`, gameplay identities, retail PView, GL ownership, and all
behavioral owners remain authoritative and unchanged.