docs(avatar): add avatar component system and glTF attachment spec

backend/.env.example

@@ -1,14 +0,0 @@
-# Database
-DATABASE_URL=postgresql://agp_user:agp_password@localhost:5432/agp_db
-
-# Redis
-REDIS_URL=redis://localhost:6379/0
-
-# JWT
-SECRET_KEY=change-me-to-a-secure-random-string
-ALGORITHM=HS256
-ACCESS_TOKEN_EXPIRE_MINUTES=30
-
-# App
-DEBUG=true
-CORS_ORIGINS=http://localhost:8080,http://localhost:3000

backend/.gitignore

@@ -1,4 +0,0 @@
-.env
-__pycache__/
-*.pyc
-.venv/

backend/app/config.py

@@ -1,32 +0,0 @@
-from pydantic_settings import BaseSettings
-from functools import lru_cache
-
-
-class Settings(BaseSettings):
-    # Database
-    DATABASE_URL: str = "postgresql+asyncpg://agp_user:agp_password@localhost:5432/agp_db"
-
-    # Redis
-    REDIS_URL: str = "redis://localhost:6379/0"
-
-    # JWT
-    SECRET_KEY: str = "change-me-to-a-secure-random-string"
-    ALGORITHM: str = "HS256"
-    ACCESS_TOKEN_EXPIRE_MINUTES: int = 30
-
-    # App
-    DEBUG: bool = True
-    CORS_ORIGINS: str = "http://localhost:8080,http://localhost:3000"
-
-    @property
-    def cors_origins_list(self) -> list[str]:
-        return [origin.strip() for origin in self.CORS_ORIGINS.split(",")]
-
-    class Config:
-        env_file = ".env"
-        case_sensitive = True
-
-
-@lru_cache()
-def get_settings() -> Settings:
-    return Settings()

backend/app/database.py

@@ -1,38 +0,0 @@
-"""Async database engine and session factory."""
-
-from sqlalchemy.ext.asyncio import (
-    AsyncSession,
-    async_sessionmaker,
-    create_async_engine,
-)
-from sqlalchemy.orm import DeclarativeBase
-
-from app.config import settings
-
-engine = create_async_engine(
-    settings.database_url,
-    echo=settings.DEBUG,
-    pool_size=10,
-    max_overflow=20,
-)
-
-async_session_factory = async_sessionmaker(
-    engine,
-    class_=AsyncSession,
-    expire_on_commit=False,
-)
-
-
-class Base(DeclarativeBase):
-    pass
-
-
-async def get_db() -> AsyncSession:
-    """Dependency that yields an async database session."""
-    async with async_session_factory() as session:
-        try:
-            yield session
-            await session.commit()
-        except Exception:
-            await session.rollback()
-            raise

backend/app/main.py

@@ -1,36 +0,0 @@
-"""FastAPI application entry point."""
-
-from contextlib import asynccontextmanager
-
-from fastapi import FastAPI
-
-from app.config import settings
-from app.routers import auth, users, worlds, assets
-
-
-@asynccontextmanager
-async def lifespan(app: FastAPI):
-    """Application lifespan: startup and shutdown events."""
-    # Startup: initialize database, connect to Redis, etc.
-    yield
-    # Shutdown: close connections, cleanup
-
-
-app = FastAPI(
-    title=settings.app_name,
-    version=settings.app_version,
-    description="Agentic Game Platform - Backend API",
-    lifespan=lifespan,
-)
-
-# Include routers
-app.include_router(auth.router, prefix="/api/auth", tags=["auth"])
-app.include_router(users.router, prefix="/api/users", tags=["users"])
-app.include_router(worlds.router, prefix="/api/worlds", tags=["worlds"])
-app.include_router(assets.router, prefix="/api/assets", tags=["assets"])
-
-
-@app.get("/api/health")
-async def health_check():
-    """Simple health check endpoint."""
-    return {"status": "ok", "app": settings.app_name}

backend/app/models/__init__.py

@@ -1,6 +0,0 @@
-from app.models.user import User
-from app.models.session import Session
-from app.models.world import World
-from app.models.asset import Asset
-
-__all__ = ["User", "Session", "World", "Asset"]

backend/app/models/asset.py

@@ -1,36 +0,0 @@
-from sqlalchemy import Column, Integer, String, ForeignKey, Text, DateTime, Enum as SAEnum
-from sqlalchemy.orm import relationship
-from sqlalchemy.sql import func
-import enum
-
-from app.database import Base
-
-
-class AssetType(str, enum.Enum):
-    IMAGE = "image"
-    AUDIO = "audio"
-    VIDEO = "video"
-    DOCUMENT = "document"
-    MODEL_3D = "model_3d"
-    OTHER = "other"
-
-
-class Asset(Base):
-    __tablename__ = "assets"
-
-    id = Column(Integer, primary_key=True, index=True)
-    name = Column(String(255), nullable=False)
-    description = Column(Text, nullable=True)
-    asset_type = Column(SAEnum(AssetType), nullable=False)
-    file_path = Column(String(512), nullable=False)
-    file_size = Column(Integer, nullable=True)
-    mime_type = Column(String(128), nullable=True)
-    metadata_json = Column(Text, nullable=True)
-    world_id = Column(Integer, ForeignKey("worlds.id"), nullable=True)
-    owner_id = Column(Integer, ForeignKey("users.id"), nullable=False)
-    is_public = Column(Integer, default=0, nullable=False)
-    created_at = Column(DateTime(timezone=True), server_default=func.now())
-    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
-
-    owner = relationship("User", back_populates="assets")
-    world = relationship("World", back_populates="assets")

backend/app/models/session.py

@@ -1,18 +0,0 @@
-from sqlalchemy import Column, String, DateTime, ForeignKey, Boolean
-from sqlalchemy.orm import relationship
-from sqlalchemy.sql import func
-from app.database import Base
-
-
-class Session(Base):
-    __tablename__ = "sessions"
-
-    id = Column(String, primary_key=True)
-    user_id = Column(String, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
-    token = Column(String, unique=True, index=True, nullable=False)
-    expires_at = Column(DateTime(timezone=True), nullable=False)
-    is_active = Column(Boolean, default=True)
-    created_at = Column(DateTime(timezone=True), server_default=func.now())
-    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
-
-    user = relationship("User", back_populates="sessions")

backend/app/models/user.py

@@ -1,21 +0,0 @@
-from sqlalchemy import Column, Integer, String, Boolean, DateTime
-from sqlalchemy.orm import relationship
-from sqlalchemy.sql import func
-
-from app.database import Base
-
-
-class User(Base):
-    __tablename__ = "users"
-
-    id = Column(Integer, primary_key=True, index=True)
-    username = Column(String(50), unique=True, index=True, nullable=False)
-    email = Column(String(120), unique=True, index=True, nullable=False)
-    hashed_password = Column(String(255), nullable=False)
-    is_active = Column(Boolean, default=True)
-    created_at = Column(DateTime(timezone=True), server_default=func.now())
-    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
-
-    sessions = relationship("Session", back_populates="user", cascade="all, delete-orphan")
-    worlds = relationship("World", back_populates="owner")
-    assets = relationship("Asset", back_populates="owner")

backend/app/models/world.py

@@ -1,27 +0,0 @@
-from sqlalchemy import Column, Integer, String, Text, DateTime, ForeignKey, Enum
-from sqlalchemy.orm import relationship
-from sqlalchemy.sql import func
-import enum
-
-from app.database import Base
-
-
-class WorldVisibility(enum.Enum):
-    PUBLIC = "public"
-    PRIVATE = "private"
-    FRIENDS_ONLY = "friends_only"
-
-
-class World(Base):
-    __tablename__ = "worlds"
-
-    id = Column(Integer, primary_key=True, index=True)
-    name = Column(String(255), nullable=False)
-    description = Column(Text, nullable=True)
-    owner_id = Column(Integer, ForeignKey("users.id"), nullable=False)
-    visibility = Column(Enum(WorldVisibility), default=WorldVisibility.PUBLIC)
-    created_at = Column(DateTime(timezone=True), server_default=func.now())
-    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
-
-    owner = relationship("User", back_populates="worlds")
-    assets = relationship("Asset", back_populates="world", cascade="all, delete-orphan")

backend/requirements.txt

@@ -1,16 +0,0 @@
-fastapi==0.115.6
-uvicorn[standard]==0.34.0
-sqlalchemy==2.0.36
-alembic==1.14.0
-psycopg2-binary==2.9.10
-redis==5.2.1
-pydantic==2.10.3
-pydantic-settings==2.7.0
-python-jose[cryptography]==3.3.0
-passlib[bcrypt]==1.7.4
-python-multipart==0.0.20
-email-validator==2.2.0
-httpx==0.28.1
-pytest==8.3.4
-pytest-asyncio==0.25.0
-pytest-cov==6.0.0

docs/architecture/avatar.md

@@ -0,0 +1,462 @@
+# Avatar Component System & glTF Attachment Spec
+
+> **Status:** Proposed
+> **Owner:** Platform team
+> **Related:** Server authority + client prediction, world chunk data format
+
+## 1. Overview
+
+This document specifies the **avatar component system** for **agp-game**, a
+Godot-based multiplayer game. It defines:
+
+- How an avatar is decomposed into **body parts** and **attachment slots**.
+- How **cosmetic attachments** (clothing, accessories, gear) mount onto the
+  base body.
+- The **glTF/GLB format requirements** that all avatar assets must satisfy so
+  they can be loaded, skinned, and networked consistently.
+
+The goal is a **modular, data-driven avatar pipeline**: a single base body rig
+plus swappable attachments, all authored in glTF and consumed by a shared Godot
+runtime. This enables player customization, cosmetic monetization, and
+server-authoritative validation of what a player is wearing.
+
+### 1.1 Design Goals
+
+- **Modularity:** Body parts and attachments are independent assets that can be
+  combined at runtime without re-exporting.
+- **Consistency:** A single, well-defined skeleton and slot convention so any
+  attachment fits any base body.
+- **Networkability:** The avatar's composition is expressed as a compact,
+  serializable **loadout** that the server can validate and replicate.
+- **Performance:** Attachments are skinned to the same skeleton and share
+  materials where possible to minimize draw calls and skinning cost.
+- **Tooling-friendly:** Assets are authored in standard glTF 2.0 and validated
+  by a build-time checker.
+
+---
+
+## 2. Avatar Decomposition
+
+### 2.1 The Base Body
+
+Every avatar is built on a **base body** — a single glTF asset containing:
+
+- A **skeleton** (the canonical rig, see §3).
+- A **base mesh** for the skin/body (head, torso, arms, legs).
+- **Attachment points** (empty nodes) that define where accessories mount.
+
+The base body is the only asset that carries the skeleton. Attachments reference
+the skeleton by **bone name** and are skinned to it; they never carry their own
+rig.
+
+### 2.2 Body Parts vs. Attachments
+
+Two distinct concepts:
+
+| Concept        | Definition                                                              | Example                          |
+|----------------|-------------------------------------------------------------------------|----------------------------------|
+| **Body part**  | A mesh that replaces part of the base body's skin (e.g., a different head, a tail, wings). | Alternate head, cybernetic arm |
+| **Attachment** | A mesh that mounts *on top of* the body without replacing it (clothing, accessories). | Shirt, hat, glasses, backpack |
+
+The distinction matters for **slot exclusivity** and **layering**:
+
+- **Body parts** are *exclusive* per slot — only one head can be equipped.
+- **Attachments** are *layered* — a hat and glasses can coexist, and both sit
+  above the head mesh.
+
+---
+
+## 3. Skeleton & Slot Convention
+
+### 3.1 Canonical Skeleton
+
+All avatars share a **canonical skeleton** with a fixed set of bone names. This
+is the contract that lets any attachment fit any body. The skeleton follows a
+humanoid convention (Godot's `Humanoid` profile / glTF VRM-style naming).
+
+Required bones (subset of the full rig):
+
+```
+Root
+├── Hips
+│   ├── Spine
+│   │   ├── Chest
+│   │   │   ├── Neck
+│   │   │   │   └── Head
+│   │   │   │       ├── HeadTop          # hat / hair mount
+│   │   │   │       ├── Jaw              # face accessories
+│   │   │   │       └── LeftEye / RightEye
+│   │   │   ├── LeftShoulder
+│   │   │   │   └── LeftUpperArm
+│   │   │   │       └── LeftLowerArm
+│   │   │   │           └── LeftHand
+│   │   │   └── RightShoulder
+│   │   │       └── RightUpperArm
+│   │   │           └── RightLowerArm
+│   │   │               └── RightHand
+│   │   └── (Chest children for torso attachments)
+│   ├── LeftUpperLeg
+│   │   └── LeftLowerLeg
+│   │       └── LeftFoot
+│   └── RightUpperLeg
+│       └── RightLowerLeg
+│           └── RightFoot
+```
+
+**Rules:**
+
+- Bone names are **case-sensitive** and must match exactly.
+- The skeleton is **T-pose** at rest for consistent skinning.
+- Attachments must be skinned to **at least** the bones they deform; static
+  accessories may be parented to a single bone (e.g., a hat parented to `Head`).
+
+### 3.2 Attachment Slots
+
+Slots are the **logical mount points** for body parts and attachments. Each slot
+maps to one or more bones and defines what can be equipped there.
+
+| Slot ID        | Category     | Mount bone(s)      | Exclusivity | Example assets                |
+|----------------|--------------|--------------------|-------------|-------------------------------|
+| `head`         | body part    | `Head`             | exclusive   | alternate head, face          |
+| `hair`         | attachment   | `HeadTop`          | exclusive   | hairstyles, hats              |
+| `face`         | attachment   | `Jaw`              | exclusive   | glasses, masks, beards        |
+| `torso`        | body part    | `Chest`            | exclusive   | alternate torso               |
+| `chest`        | attachment   | `Chest`            | exclusive   | shirts, armor, chest gear     |
+| `back`         | attachment   | `Chest` (back)     | exclusive   | backpacks, wings, capes       |
+| `left_arm`     | body part    | `LeftUpperArm`     | exclusive   | alternate arm                 |
+| `right_arm`    | body part    | `RightUpperArm`    | exclusive   | alternate arm                 |
+| `left_hand`    | attachment   | `LeftHand`         | exclusive   | gloves, weapons (held)        |
+| `right_hand`   | attachment   | `RightHand`        | exclusive   | gloves, weapons (held)        |
+| `legs`         | body part    | `Hips`             | exclusive   | alternate legs                |
+| `pants`        | attachment   | `Hips`             | exclusive   | pants, skirts                 |
+| `left_foot`    | attachment   | `LeftFoot`         | exclusive   | shoes                         |
+| `right_foot`   | attachment   | `RightFoot`        | exclusive   | shoes                         |
+| `accessory`    | attachment   | `Root` (free)      | multiple    | belts, jewelry, floating items|
+
+**Slot semantics:**
+
+- **`exclusive`** slots allow at most one equipped item at a time.
+- The **`accessory`** slot is *multi-slot* — multiple accessories may be equipped
+  simultaneously (bounded by a configurable limit, e.g., 8).
+- **Body-part slots** (`head`, `torso`, `legs`, `left_arm`, `right_arm`) replace
+  the corresponding base mesh. When a body part is equipped, the base mesh for
+  that region is hidden.
+- **Attachment slots** layer on top of the base mesh and never hide it.
+
+### 3.3 Slot → Bone Mapping
+
+Each slot declares a **primary mount bone** and an optional **secondary bone
+list** for skinning. The runtime uses this to:
+
+1. Parent static accessories to the mount bone.
+2. Skin skinned attachments to the union of the slot's bones.
+
+---
+
+## 4. glTF/GLB Format Requirements
+
+All avatar assets (base bodies, body parts, attachments) are distributed as
+**glTF 2.0** (`.gltf` + external buffers/textures) or **GLB** (`.glb`, binary
+container). GLB is the preferred distribution format for runtime loading.
+
+### 4.1 Required Conventions
+
+| Concern            | Requirement                                                                 |
+|--------------------|------------------------------------------------------------------------------|
+| **Format**         | glTF 2.0 (`.gltf` or `.glb`). GLB preferred for runtime.                     |
+| **Coordinate system** | glTF standard: **+Y up, +Z forward, right-handed**. Godot converts to its own convention on import. |
+| **Units**          | Meters. Avatar height ~1.8 m at the `Root` bone.                              |
+| **Skeleton**       | Single skeleton per asset; bone names per §3.1.                              |
+| **Skinning**       | `skins` + `nodes` with `JOINTS_0` / `WEIGHTS_0` accessors.                    |
+| **Pose**           | T-pose at rest.                                                              |
+| **Materials**      | PBR metallic-roughness. Use `KHR_materials_unlit` for emissive/UI-only items. |
+| **Textures**       | Max 2048×2048; power-of-two preferred. Use `KHR_texture_basisu` (BasisU) for runtime. |
+| **Animation**      | Optional. If present, must not rename or remove canonical bones.             |
+
+### 4.2 Asset Metadata (extras)
+
+Each asset **must** declare its slot and identity in the glTF `asset.extras`
+object. This is the machine-readable contract consumed by the build pipeline and
+runtime.
+
+```json
+{
+  "asset": {
+    "version": "2.0",
+    "extras": {
+      "agp": {
+        "type": "attachment",          // "base_body" | "body_part" | "attachment"
+        "slot": "chest",               // slot ID from §3.2
+        "id": "shirt_bandit_01",       // globally unique asset id
+        "display_name": "Bandit Shirt",
+        "version": "1.0.0",
+        "mount_bone": "Chest",         // primary mount bone
+        "skin_bones": ["Chest", "Spine", "LeftUpperArm", "RightUpperArm"],
+        "exclusive": true,             // matches slot exclusivity
+        "tags": ["cloth", "common"],
+        "author": "platform-team"
+      }
+    }
+  }
+}
+```
+
+**Validation rules for `extras.agp`:**
+
+- `type` must be one of `base_body`, `body_part`, `attachment`.
+- `slot` must be a known slot ID (§3.2).
+- `mount_bone` must exist in the canonical skeleton.
+- `skin_bones` must all exist in the canonical skeleton.
+- `exclusive` must match the slot's declared exclusivity.
+- `id` must be unique across the asset catalog.
+
+### 4.3 Node Naming Convention
+
+To make assets self-describing and mergeable, nodes follow a convention:
+
+- **Base body:** the mesh node is named `Body`; the skeleton root is `Root`.
+- **Body part:** the mesh node is named `<SlotID>_Mesh` (e.g., `head_Mesh`).
+- **Attachment:** the mesh node is named `<SlotID>_<AssetID>` (e.g.,
+  `chest_shirt_bandit_01`).
+- **Attachment points** (empty nodes) on the base body are named
+  `attach_<slot>` (e.g., `attach_head`, `attach_left_hand`).
+
+### 4.4 Material & Texture Requirements
+
+- All materials use the **metallic-roughness** PBR model.
+- Textures are embedded in the GLB or referenced as external files; external
+  references must be relative paths within the asset package.
+- **Color customization** is supported via a `baseColorFactor` tint applied at
+  runtime (multiplied over the albedo). Assets should use a neutral albedo
+  (white/gray) where tinting is intended.
+- **Masked/transparent** materials must set the correct alpha mode
+  (`MASK` or `BLEND`) and `alphaCutoff`.
+
+### 4.5 Skeleton Merging at Runtime
+
+When an attachment is loaded, the runtime **merges** it onto the base body:
+
+1. Load the base body (skeleton + base meshes).
+2. Load each equipped attachment.
+3. For each attachment, **re-target its skin** to the base body's skeleton by
+   bone name (no re-export needed).
+4. Parent static accessories to their `mount_bone`.
+5. Hide base meshes for any equipped body-part slots.
+6. Apply material tints and merge into the render tree.
+
+The merge is **name-based** — bone names must match exactly (§3.1). This is the
+core reason for the strict naming contract.
+
+---
+
+## 5. Loadout Model (Network & Persistence)
+
+The avatar's composition is serialized as a **loadout** — a compact, ordered
+list of equipped asset IDs. This is what the server validates, persists, and
+replicates.
+
+### 5.1 Loadout JSON
+
+```json
+{
+  "base_body": "base_human_male_01",
+  "slots": {
+    "head":   "head_cyber_01",
+    "hair":   "hair_mohawk_01",
+    "face":   null,
+    "torso":  null,
+    "chest":  "chest_bandit_01",
+    "back":   "backpack_01",
+    "left_arm":  null,
+    "right_arm": null,
+    "left_hand": "glove_leather_01",
+    "right_hand": "glove_leather_01",
+    "legs":   null,
+    "pants":  "pants_cargo_01",
+    "left_foot":  "shoe_boot_01",
+    "right_foot": "shoe_boot_01",
+    "accessory": ["belt_01", "necklace_01"]
+  }
+}
+```
+
+**Rules:**
+
+- `base_body` is required and must reference a valid `base_body` asset.
+- Each exclusive slot holds **at most one** asset id (or `null`).
+- `accessory` is an array (0..N, bounded).
+- The server validates that every id exists in the catalog and that slot
+  exclusivity is respected.
+
+### 5.2 Network Replication
+
+The loadout is replicated as part of the player's spawn/state data:
+
+```
+spawn_entity:
+  entity_id: uint32
+  type: player
+  transform: { x, y, rot }
+  props:
+    loadout_hash: uint32      # hash of the loadout for change detection
+    loadout: { ... }          # full loadout on spawn / on change
+```
+
+- The **full loadout** is sent on spawn and whenever it changes (reliable).
+- A **`loadout_hash`** lets clients skip re-resolving assets if unchanged.
+- The server is the **authority** on the loadout; clients send *requests* to
+  change equipment, and the server validates and broadcasts the result.
+
+### 5.3 Server-Side Validation
+
+The server rejects a loadout if:
+
+- `base_body` is missing or unknown.
+- Any slot references an unknown asset id.
+- An exclusive slot has more than one item.
+- An asset's declared `slot` does not match the slot it is placed in.
+- The accessory list exceeds the configured limit.
+- The asset is not owned/unlocked by the player (for gated cosmetics).
+
+---
+
+## 6. Godot Runtime Architecture
+
+### 6.1 Node Structure
+
+```
+Avatar (Node3D)
+├── Skeleton3D            # canonical skeleton (from base body)
+├── BodyMeshes            # base body meshes (skinned to Skeleton3D)
+│   ├── head_Mesh
+│   ├── torso_Mesh
+│   └── ...
+├── Attachments           # equipped attachments
+│   ├── chest_shirt_bandit_01
+│   ├── hair_mohawk_01
+│   └── ...
+└── AttachmentPoints      # empty nodes for dynamic mounting
+    ├── attach_head
+    ├── attach_left_hand
+    └── ...
+```
+
+### 6.2 Core Classes
+
+| Class                    | Responsibility                                              |
+|--------------------------|-------------------------------------------------------------|
+| `AvatarSystem`           | Loads base body + attachments, resolves loadouts, owns the avatar node. |
+| `AvatarLoader`           | glTF/GLB import, skeleton merge, skin re-targeting.          |
+| `AvatarSlotRegistry`     | Static registry of slot definitions (id, bones, exclusivity).|
+| `AvatarLoadout`          | Serializable loadout model + validation.                    |
+| `AvatarCatalog`          | Asset catalog (id → asset metadata + resource path).         |
+| `AvatarVisualizer`       | Builds the render tree from a loadout.                      |
+
+### 6.3 Loading Pipeline
+
+```
+loadout JSON
+   │
+   ▼
+AvatarCatalog.resolve(loadout)   # id → asset metadata + GLB path
+   │
+   ▼
+AvatarLoader.load_base_body()    # import GLB, extract skeleton + base meshes
+   │
+   ▼
+for each equipped slot:
+   AvatarLoader.load_attachment()# import GLB, re-target skin to skeleton
+   │
+   ▼
+AvatarVisualizer.assemble()      # parent, hide replaced parts, apply tints
+   │
+   ▼
+Avatar node ready for render
+```
+
+### 6.4 Performance Considerations
+
+- **Shared skeleton:** All meshes skin to one `Skeleton3D`, so skinning is
+  computed once per frame.
+- **Material batching:** Attachments that share a material are merged into a
+  single mesh where possible (static accessories).
+- **LOD:** Optional LOD variants per asset; the runtime selects based on
+  distance.
+- **Caching:** Resolved loadouts and imported GLB resources are cached by
+  `AvatarCatalog` to avoid re-importing on respawn or re-join.
+
+---
+
+## 7. Asset Pipeline & Validation
+
+### 7.1 Build-Time Validation
+
+A build-time checker validates every asset before it enters the catalog:
+
+1. **Format check:** valid glTF 2.0 / GLB.
+2. **Metadata check:** `extras.agp` present and valid (§4.2).
+3. **Skeleton check:** all `skin_bones` exist in the canonical skeleton.
+4. **Slot check:** `slot` is known and `exclusive` matches.
+5. **Mesh check:** meshes are skinned (or static accessories parented to a bone).
+6. **Texture check:** sizes, formats, and alpha modes are valid.
+7. **Uniqueness check:** `id` is unique.
+
+### 7.2 Catalog Manifest
+
+The catalog is a JSON manifest mapping asset ids to metadata and resource paths:
+
+```json
+{
+  "assets": {
+    "base_human_male_01": {
+      "type": "base_body",
+      "path": "res://assets/avatars/base_human_male_01.glb",
+      "version": "1.0.0"
+    },
+    "chest_bandit_01": {
+      "type": "attachment",
+      "slot": "chest",
+      "path": "res://assets/avatars/chest_bandit_01.glb",
+      "version": "1.0.0"
+    }
+  }
+}
+```
+
+---
+
+## 8. Security & Anti-Cheat
+
+- **Server-authoritative loadouts:** Clients only *request* equipment changes;
+  the server validates against the catalog and the player's owned items.
+- **No client asset injection:** Clients cannot send arbitrary GLB data; they
+  reference catalog ids only.
+- **Rate limiting:** Equipment-change requests are rate-limited per peer.
+- **Hash verification:** The `loadout_hash` lets the server detect tampered or
+  stale loadout state.
+
+---
+
+## 9. Open Questions / Future Work
+
+- **Morph targets / blendshapes:** Support for facial expressions and body
+  morphs (e.g., height, muscle) via glTF morph targets.
+- **Physics attachments:** Cloth simulation for capes/skirts (Godot cloth).
+- **Dynamic tinting UI:** A color-picker that writes `baseColorFactor` tints.
+- **VRM compatibility:** Consider supporting VRM (a glTF extension for
+  humanoid avatars) as an import source.
+- **Attachment LOD streaming:** Streaming high-res attachments on demand.
+
+---
+
+## 10. Summary
+
+| Concern                | Decision                                              |
+|------------------------|-------------------------------------------------------|
+| Format                 | glTF 2.0 / GLB (GLB preferred for runtime)            |
+| Skeleton               | Single canonical humanoid skeleton, name-based merge  |
+| Slots                  | Fixed slot registry; exclusive body parts + layered attachments |
+| Loadout                | Compact JSON; server-authoritative and validated      |
+| Replication            | Full loadout on spawn/change + `loadout_hash`         |
+| Runtime                | Godot `Skeleton3D` + name-based skin re-targeting     |
+| Validation             | Build-time asset checker + runtime catalog validation |