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Guidebook Modelling Troubleshooting

Every modelling failure, with the exact log line and the fix. General debugging loop: Guidebook Debugging.

Symptom Log line ([gregCore][Mods] …) Fix
Registration returns false, no item ObjImport: No .obj path model must end in .obj (case-insensitive)
Registration returns false ObjImport: File not found Filename typo or wrong subfolder; model is relative to the (sub)folder you passed
Registration returns false ObjImport: File too large (… limit 67108864) Decimate/compress below 64 MB, re-export
Registration returns false Path escapes the pack folder No .., /, or absolute paths in model/subfolder — keep files inside the mod folder
Registration returns false Import failed / Import returned null / Import has no vertices Broken OBJ: re-export with normals + UVs, triangulated, no zero-area faces (see Guidebook Modelling OBJ Blender)
Registration aborted Mesh precheck negative - registration aborted Any of the above — fix the mesh, not the spec
false, folder complaint Pack folder missing / Pack folder or folder name empty Create the subfolder; pass its name exactly
false, no model No ModelFile specified model key missing/empty in the spec
false on C# early call ModLoader.instance not available (scene not ready yet?) Register after load (e.g. OnReady/scene state), never in a static constructor
Item registers but looks wrong (no error) scale/size_u pass-through: adjust spec, check ColliderSize/Center against mesh bounds
Item registers, surface broken (no error) Multi-material or missing UVs — single material + unwrapped UVs, re-export
Wrong shop behaviour/type (no error) type must be a valid PlayerManager.ObjectInHand name (case-insensitive); invalid → vanilla default
Old item ID reused save/load anomalies Never reuse IDs or GUIDs (ranges 100, 1000/2000/3000, 9001+); see Developer Shop Items

Still stuck: minimal repro (one OBJ + 5-line spec), full log excerpt with the ObjImport:/CustomItems: lines, and the exact spec table → mod tracker or Discord.