feat(validation): show toast notification when GLB errors are detected on reload

docs/ARTIST_GUIDE.md

@@ -1019,6 +1019,28 @@ Use your own namespace (e.g., `mycreator`) to avoid conflicts with the base mod
 
 ---
 
+## Validation & Debugging
+
+The mod includes built-in tools to help you catch issues with your GLB files.
+
+### `/tiedup validate` Command
+
+Run `/tiedup validate` in-game (client-side command) to see a diagnostic report for all loaded GLBs:
+
+- **RED** errors — item won't work (missing GLB, invalid file, no skin)
+- **YELLOW** warnings — item works but something looks wrong (bone typo, multiple meshes, no Idle animation)
+- **GRAY** info — informational (custom bones detected, vertex count)
+
+Filter by item: `/tiedup validate tiedup:leather_armbinder`
+
+The validation runs automatically on every resource reload (F3+T). Check your game log for a summary line: `[GltfValidation] Validated N GLBs: X passed, Y with warnings, Z with errors`.
+
+### Mesh Naming Convention
+
+If your GLB contains multiple meshes, name your item mesh `Item` in Blender. The mod prioritizes a mesh named `Item` over other meshes. If no `Item` mesh is found, the last non-`Player` mesh is used (backward compatible, but may pick the wrong one in multi-mesh files).
+
+---
+
 ## Common Mistakes
 
 ### Skeleton Issues
@@ -1034,7 +1056,7 @@ Use your own namespace (e.g., `mycreator`) to avoid conflicts with the base mod
 
 | Mistake | Symptom | Fix |
 |---------|---------|-----|
-| Action not prefixed with `PlayerArmature\|` | Animation not found, falls back to first clip | Rename: `Idle` → `PlayerArmature\|Idle` |
+| Action not prefixed with `PlayerArmature\|` | Animation not found, falls back to first clip | Rename: `Idle` → `PlayerArmature\|Idle`. Note: the mod strips any `ArmatureName\|` prefix, so custom armature names also work. |
 | Wrong case (`idle` instead of `Idle`) | Animation not found | Use exact PascalCase: `Idle`, `SitIdle`, `KneelStruggle` |
 | Variant gap (`.1`, `.2`, `.4` — missing `.3`) | Only .1 and .2 are used | Number sequentially with no gaps |
 | Animating bones outside your regions | Keyframes silently ignored | Only animate bones in your declared regions |
@@ -1553,11 +1575,15 @@ NEVER DO:
 
 GOOD TO KNOW:
   → Only Idle is required. Everything else has fallbacks.
+  → animation_bones is optional. Omit it and all owned bones work for all animations.
   → Templates let you skip animation entirely.
+  → Custom bones are supported — add chain/ribbon/twist bones parented to standard bones.
   → Free bones (not owned by any item) CAN be animated by your GLB.
   → Bones owned by another equipped item are always ignored.
   → The mod handles sitting, sneaking, walking — you don't have to.
   → Context GLBs in tiedup_contexts/ replace default postures.
+  → Name your item mesh "Item" in Blender for explicit selection in multi-mesh files.
+  → Run /tiedup validate in-game to check your GLBs for issues.
   → Slim model is optional. Steve mesh works on Alex (minor clipping).
   → Textures bake into the GLB. No separate file needed.
 ```