Studio (#4237)

* Rebuild Studio branch on top of main

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix security and code quality issues for Studio PR #4237

- Validate models_dir query param against allowed directory roots
  to prevent path traversal in /api/models/local endpoint
- Replace string startswith() with Path.is_relative_to() for
  frontend path traversal check in serve_frontend
- Sanitize SSE error messages to not leak exception details to
  clients (4 locations in inference.py)
- Bind port-discovery socket to 127.0.0.1 instead of all interfaces
  in llama_cpp backend
- Import datasets_root and resolve_output_dir in embedding training
  function to fix NameError and use managed output directory
- Remove stale .gitignore entries for package-lock.json and test
  directories so tests can be tracked in version control
- Add venv-reexecution logic to ui CLI command matching the studio
  command behavior

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Move models_dir path validation before try/except block

The HTTPException(403) was inside the try/except Exception handler,
so it would be caught and re-raised as a 500. Moving the validation
before the try block ensures the 403 is returned directly and also
makes the control flow clearer for static analysis (path is validated
before any filesystem operations).

* Use os.path.realpath + startswith for models_dir validation

CodeQL py/path-injection does not recognize Path.is_relative_to() as
a sanitizer. Switched to os.path.realpath + str.startswith which is
a recognized sanitizer pattern in CodeQL's taint analysis. The
startswith check uses root_str + os.sep to prevent prefix collisions
(e.g. /app/models_evil matching /app/models).

* Never pass user input to Path constructor in models_dir validation

CodeQL traces taint through Path(resolved) even after a startswith
barrier guard. Fix: the user-supplied models_dir is only used as a
string for comparison against allowed roots. The Path object passed
to _scan_models_dir comes from the trusted allowed_roots list, not
from user input. This fully breaks the taint chain.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

studio/backend/utils/utils.py

@@ -0,0 +1,118 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+
+"""
+Shared backend utilities
+"""
+
+import os
+import structlog
+from loggers import get_logger
+from contextlib import contextmanager
+from pathlib import Path
+import shutil
+import tempfile
+
+
+logger = get_logger(__name__)
+
+
+@contextmanager
+def without_hf_auth():
+    """
+    Context manager to temporarily disable HuggingFace authentication.
+
+    Usage:
+        with without_hf_auth():
+            # Code that should run without cached tokens
+            model_info(model_name, token=None)
+    """
+    # Save environment variables
+    saved_env = {}
+    env_vars = ["HF_TOKEN", "HUGGINGFACE_HUB_TOKEN", "HF_HOME"]
+    for var in env_vars:
+        if var in os.environ:
+            saved_env[var] = os.environ[var]
+            del os.environ[var]
+
+    # Save disable flag
+    saved_disable = os.environ.get("HF_HUB_DISABLE_IMPLICIT_TOKEN")
+    os.environ["HF_HUB_DISABLE_IMPLICIT_TOKEN"] = "1"
+
+    # Move token files temporarily
+    token_files = []
+    token_locations = [
+        Path.home() / ".cache" / "huggingface" / "token",
+        Path.home() / ".huggingface" / "token",
+    ]
+
+    for token_loc in token_locations:
+        if token_loc.exists():
+            temp = tempfile.NamedTemporaryFile(delete = False)
+            temp.close()
+            shutil.move(str(token_loc), temp.name)
+            token_files.append((token_loc, temp.name))
+
+    try:
+        yield
+    finally:
+        # Restore tokens
+        for original, temp in token_files:
+            try:
+                original.parent.mkdir(parents = True, exist_ok = True)
+                shutil.move(temp, str(original))
+            except Exception as e:
+                logger.error(f"Failed to restore token {original}: {e}")
+
+        # Restore environment
+        for var, value in saved_env.items():
+            os.environ[var] = value
+
+        if saved_disable is not None:
+            os.environ["HF_HUB_DISABLE_IMPLICIT_TOKEN"] = saved_disable
+        else:
+            os.environ.pop("HF_HUB_DISABLE_IMPLICIT_TOKEN", None)
+
+
+def format_error_message(error: Exception, model_name: str) -> str:
+    """
+    Format user-friendly error messages for common issues.
+
+    Args:
+        error: The exception that occurred
+        model_name: Name of the model being loaded
+
+    Returns:
+        User-friendly error string
+    """
+    error_str = str(error).lower()
+    model_short = model_name.split("/")[-1] if "/" in model_name else model_name
+
+    if "repository not found" in error_str or "404" in error_str:
+        return f"Model '{model_short}' not found. Check the model name."
+
+    if "401" in error_str or "unauthorized" in error_str:
+        return f"Authentication failed for '{model_short}'. Please provide a valid HF token."
+
+    if "gated" in error_str or "access to model" in error_str:
+        return f"Model '{model_short}' requires authentication. Please provide a valid HF token."
+
+    if "invalid user token" in error_str:
+        return "Invalid HF token. Please check your token and try again."
+
+    if (
+        "memory" in error_str
+        or "cuda" in error_str
+        or "mlx" in error_str
+        or "out of memory" in error_str
+    ):
+        from utils.hardware import get_device
+
+        device = get_device()
+        device_label = {"cuda": "GPU", "mlx": "Apple Silicon GPU", "cpu": "system"}.get(
+            device.value, "GPU"
+        )
+        return f"Not enough {device_label} memory to load '{model_short}'. Try a smaller model or free memory."
+
+    # Generic fallback
+    return str(error)