Plan the v0.6.0 graphics pass and add Blender-authored NPC assets

docs/adr/0013-blender-authored-npc-characters.md

@@ -0,0 +1,85 @@
+# ADR-0013: Blender-authored NPC characters and baked materials
+
+- **Status:** Proposed
+- **Date:** 2026-11-01
+
+## Context
+
+NPCs are the procedural capsule-and-box rig from
+[ADR-0010](0010-procedural-npc-presentation.md): articulated `Node3D` limbs,
+flat `StandardMaterial3D` colors, and sphere hair/eyes. ADR-0010 accepted this
+as a placeholder and recorded that a later skinned-mesh pass would replace the
+rig while keeping the `Head` contract. The props already moved to generated
+`.glb` assets ([ADR-0012](0012-surface-materials-and-generated-props.md)), but
+people remain the lowest-fidelity part of the scene: no UVs, no baked normal or
+ambient-occlusion maps, and silhouettes built from capsules.
+
+The project renders with the **GL Compatibility** backend (no SSAO/SSIL), so
+visual quality has to come from the assets and baked maps rather than a renderer
+change. CI must stay offline: the Blender step is a developer tool, not a build
+dependency.
+
+## Decision
+
+1. **Author the NPC body in Blender** and export a skinned, UV-mapped base mesh
+   as `assets/models/generated/npc_base.glb`, driven by a new
+   `tools/npc_pipeline.py` (`build` / `audit`) invoked through the Blender
+   flatpak in headless mode. The `.blend` source is committed under
+   `assets/models/npc/`.
+2. **Bake material maps in Blender** — neutral albedo, normal, and a packed ORM
+   (occlusion/roughness/metallic) map per material slot (`skin`, `cloth`,
+   `pants`, `accessory`, `hair`). Ambient occlusion is baked into the albedo or
+   the ORM R channel, since Compatibility has no screen-space AO.
+3. **Keep a procedural fallback.** `NpcAvatar` loads the imported `PackedScene`
+   when it exists and falls back to the current `_build_body()` rig otherwise,
+   mirroring `WorldBuilder._add_prop_model()`. Committed assets mean CI never
+   needs Blender, and the headless suite runs against the fallback when the
+   import is absent.
+4. **Preserve the `Head` contract and seed determinism.** The armature bones are
+   named after the current nodes (`Head`, `HipL/R`, `KneeL/R`, `ShoulderL/R`,
+   `ElbowL/R`, `HandL/R`); `outfit_for` and friends stay pure and drive the
+   material slots. A thin `_set_limb_rotation()` wrapper lets `_animate()` /
+   `_idle_layer()` target either `Node3D` pivots or `Skeleton3D` bones.
+5. **AI tooling supplies art direction only.** `tools/asset_pipeline.py`
+   generates seamless clothing albedos, `tools/model_pipeline.py`'s palette
+   helpers (`dominant_colors`, `assign_roles`) derive per-role palettes from
+   concept sheets, and `tools/screen_designs.py judge` closes the loop. All AI
+   outputs are committed; generation is dev-time and never a runtime or CI
+   dependency.
+
+## Consequences
+
+### Positive
+
+- NPCs gain real geometry, UVs, and baked normal/AO/roughness, so they read as
+  people at cinematic distance without a renderer switch.
+- Skinned meshes collapse ~33 draw calls per avatar into one, which can offset
+  the skinning cost at `MAX_LIVE_NPCS = 16`.
+- The asset contract stays behind the same `.glb` + audit discipline that props
+  already use; the procedural fallback keeps offline CI deterministic.
+- AO baked into the maps compensates for the absence of SSAO in Compatibility.
+
+### Negative
+
+- A new toolchain (Blender flatpak + `npc_pipeline.py`) and its path/colour-space
+  gotchas enter the repo; contributors must run `audit` after changing the
+  `.blend`.
+- Skinning shifts cost from draw calls to CPU; the 16-NPC frame budget must be
+  re-measured before raising the cap.
+- Two avatar backends (skinned + fallback) must stay behaviourally identical, or
+  tests that assume the fallback will silently pass against one and not the
+  other.
+
+## Alternatives considered
+
+- **Keep the procedural rig and only add textures.** Rejected: textures on
+  capsules do not fix the silhouette; the rig is the fidelity ceiling.
+- **Use Mixamo / a downloaded skinned character.** Rejected: licensing and
+  retargeting overhead exceed the value; a low-poly base authored in-house keeps
+  the art direction and the `Head`/bone contract under our control.
+- **Switch the renderer to Forward+ for SSAO/SSIL.** Rejected as a prerequisite;
+  it would break the Web export assumptions. A desktop-only Forward+ preset
+  remains a follow-up, not a dependency of this decision.
+- **A 3D-model (image-to-mesh) API instead of Blender.** Rejected for characters;
+  output topology is not controllable enough to satisfy the bone/UV contract.
+  It remains a possible prop-only follow-up (ADR-0012).