fix(studio): custom folder scan fails to find GGUF variants when pointing directly at a model directory

[danielhanchen]

Staging mirror of unslothai#4860

Original PR: unslothai#4860
Author: JYYYYYT

This is a staging copy for review and editing. Once finalized, changes will be pushed back to the original PR.

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Original description

Problem

When adding a custom scan folder that points directly at a model directory
(e.g. /path/to/gemma-4-e2b-it-gguf/ containing config.json and
gemma-4-E2B-it-BF16.gguf), the model list shows individual .gguf files
as separate entries instead of recognizing the directory as a single model.

Clicking any of these entries shows "No GGUF variants found" because
list_local_gguf_variants receives a file path instead of a directory path
and is_dir() returns False.

Additionally, _scan_lmstudio_dir misidentifies the model directory as an
LM Studio publisher folder, creating duplicate broken entries.

Steps to reproduce

1. Download a GGUF model repo locally (e.g. gemma-4-e2b-it-gguf/ with
   config.json, gemma-4-E2B-it-BF16.gguf, mmproj-BF16.gguf)
2. In Studio, click Select Model → Custom Folders and add the path
   pointing directly at the model directory
3. Two entries appear (gemma-4-E2B-it-BF16 and mmproj-BF16) instead
   of one (gemma-4-e2b-it-gguf)
4. Clicking either entry shows "No GGUF variants found"
5. Scanning the parent directory works for the top-level entry but still
   produces duplicate broken entries from the LM Studio scanner

For example

/Users/shisheng/Documents/llm-workspace/models/gemma-4-E2B-it-gguf/
├── config.json
├── configuration.json
├── gemma-4-E2B-it-BF16.gguf (9.3 GB)
├── imatrix_unsloth.gguf_file
└── mmproj-BF16.gguf (987 MB)

When I add the directory above as a custom model folder, I see two entries:

And when I add the /Users/shisheng/Documents/llm-workspace/models/ directory as a custom model folder, I see these entries:

Related Issues

After searching the issue tracker, I found no existing reports for this bug. This PR directly addresses the issue with a minimal fix.

Fix

1. _scan_models_dir — detect self-as-model (routes/models.py)

Before scanning subdirectories, check whether the directory itself is a
model: it must have both a config file (config.json or
adapter_config.json) and weight files (.gguf, .safetensors, or
.bin). Both conditions are required to avoid false positives:

• A bare directory with loose .gguf files (no config) may be a mixed
  collection → should list files individually (existing behavior)
• A config.json alone (no weights) is not a model directory

2. _scan_lmstudio_dir — skip model directories (routes/models.py)

• Early-return when the scanned directory itself has config files (it's a
  model, not a publisher structure)
• Skip child direct