feat(rendering): contain incremental render scene

Pin Arch behind acdream-owned identities, deltas, queries, generation gates, and memory diagnostics. The new five-archetype store is unbound and non-drawing so static publication can be shadowed without changing production behavior.

Co-authored-by: Erik Nilsson <erikn@users.noreply.github.com>

docs/research/2026-07-24-arch-render-scene-dependency.md

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+# 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.