Record NPC sourcing decision and crowd prototypes

docs/adr/0015-npc-model-variety-sourcing.md

@@ -0,0 +1,72 @@
+# ADR-0015: NPC model variety sourcing
+
+- **Status:** Accepted (post-0.10.0 planning)
+- **Date:** 2026-11-03
+
+## Context
+
+The library has eight skinned characters, and role/seed selection reuses them
+across the three venues. Crowds therefore repeat the same faces, builds and
+outfits. The existing contract is strict: `npc_base` mesh node, 13 named bones at
+fixed rest positions, five tint slots, front on Blender −Y and an 8,000
+triangle/vertex budget.
+
+A review compared free/open-source sources against that contract. Quaternius
+Ultimate Modular (CC0), Kenney Blocky Characters (CC0), Khronos CesiumMan and
+RiggedFigure (CC BY 4.0) and the MakeHuman base mesh (CC0) were imported and
+measured. None was a drop-in; the full results are in
+[`docs/npc-model-sourcing.md`](../npc-model-sourcing.md).
+
+## Decision
+
+1. **Ship only CC0, or CC BY with recorded attribution.** No service asset whose
+   terms restrict redistribution may be used.
+2. **Extend the project-owned procedural generator as the primary path** for
+   shipped NPC variety. The first target is four crowd-variety looks, bringing
+   the library to twelve characters.
+3. **Keep Quaternius as a reviewed reference/prototype, not a shipped base.** A
+   contract retarget is a no-go because the source is a T-pose 62-bone realistic
+   rig with substantially different proportions from the arm-down 13-bone
+   contract. A future external-rig path would need its own ADR covering its
+   skeleton, animation source and per-model gear offsets.
+4. **MakeHuman is deferred to a separate local development pipeline.** Its CC0
+   base mesh can be decimated into budget, but it needs retopology, a custom rig
+   and project-owned clothing before it is usable. It must not become a CI or
+   build dependency.
+5. **Commit research previews with attribution.** CC-BY preview images are
+   development-only and are not bundled with the game or its release packages.
+
+## Consequences
+
+### Positive
+
+- The shipped library keeps one art direction, one skeleton and one audit gate.
+- Crowd variety lands without a new runtime dependency or a second animation
+  system.
+- The licence position is simple: project-owned assets plus explicit CC-BY
+  attribution where a preview or future asset requires it.
+- The Quaternius evaluation removes a tempting but high-risk retarget from the
+  critical path.
+
+### Negative
+
+- Procedural variation is still limited by the existing face and clothing
+  vocabulary; four variants do not provide full age/body diversity.
+- Quaternius' animation set remains unused unless a second rig path is approved.
+- MakeHuman body-shape diversity is postponed.
+- External previews add a small documentation footprint that must stay out of
+  release packages.
+
+## Alternatives considered
+
+- **Retarget Quaternius onto the `npc_base` contract.** Rejected for now:
+  welding brings the geometry inside budget, but the rest pose and body
+  proportions differ enough that a contract rebuild would either distort the
+  model or require a full proportion warp.
+- **Use Quaternius' own rig and animations directly.** Deferred: attractive
+  animation quality, but it adds a second skeleton/animation path and per-model
+  gear offsets to `NpcAvatar`.
+- **Use MakeHuman as the primary body source.** Rejected for this milestone: high
+  polygon count, no rig in the base mesh and a separate authoring dependency.
+- **Use Mixamo or Ready Player Me.** Rejected: service terms are not a simple
+  free/open-source redistribution basis for shipped meshes.

docs/adr/README.md

@@ -18,3 +18,4 @@ Each ADR records the context, decision, consequences and alternatives for a dura
 - [0012-surface-materials-and-generated-props](0012-surface-materials-and-generated-props.md)
 - [0013-blender-authored-npc-characters](0013-blender-authored-npc-characters.md)
 - [0014-runtime-image-root](0014-runtime-image-root.md)
+- [0015-npc-model-variety-sourcing](0015-npc-model-variety-sourcing.md)