studio: fix stale GGUF metadata, update helper model, auth improvements (#4346)

* studio: switch helper model to Qwen3.5-4B-GGUF

Replace Qwen3-4B-Instruct-2507-GGUF with Qwen3.5-4B-GGUF as the
default helper model for LLM-assisted dataset detection. Same
UD-Q4_K_XL variant.

* studio: fix stale GGUF metadata when switching models (#4347)

Reset _supports_reasoning, _supports_tools, _context_length, and
_chat_template at the start of _read_gguf_metadata() to prevent
stale settings from a previous model leaking into the next load.

Co-authored-by: Daniel Han <daniel@unsloth.ai>

* studio: change login error to "Incorrect password", add reset-password CLI

- Login error now says "Incorrect password" instead of the generic
  "Incorrect username or password" since Studio only has one account.
- Add `unsloth studio reset-password` command that deletes the auth
  database so a fresh admin account with a new random password is
  created on the next server start.

* studio: include reset command in login error message

* studio: change password setup subtitle wording

cli/commands/studio.py

@@ -178,3 +178,28 @@ def setup():
 
     if result.returncode != 0:
         raise typer.Exit(result.returncode)
+
+
+# ── unsloth studio reset-password ────────────────────────────────────
+
+
+@studio_app.command("reset-password")
+def reset_password():
+    """Reset the Studio admin password.
+
+    Deletes the auth database so that a fresh admin account with a new
+    random password is created on the next server start.  The Studio
+    server must be restarted after running this command.
+    """
+    auth_dir = STUDIO_HOME / "auth"
+    db_file = auth_dir / "auth.db"
+    pw_file = auth_dir / ".bootstrap_password"
+
+    if not db_file.exists():
+        typer.echo("No auth database found -- nothing to reset.")
+        raise typer.Exit(0)
+
+    db_file.unlink(missing_ok = True)
+    pw_file.unlink(missing_ok = True)
+
+    typer.echo("Auth database deleted. Restart Unsloth Studio to get a new password.")

studio/backend/core/inference/llama_cpp.py

@@ -446,6 +446,13 @@ class LlamaCppBackend:
         Parses only the KV pairs we need (~30ms even for multi-GB files).
         For split GGUFs, metadata is always in shard 1.
         """
+        # Reset metadata from any previously loaded model so stale flags
+        # (eg _supports_reasoning) do not carry over when switching models.
+        self._context_length = None
+        self._chat_template = None
+        self._supports_reasoning = False
+        self._supports_tools = False
+
         try:
             WANTED = {"general.architecture", "tokenizer.chat_template"}
             arch = None

studio/backend/routes/auth.py

@@ -54,14 +54,14 @@ async def login(payload: AuthLoginRequest) -> Token:
     if record is None:
         raise HTTPException(
             status_code = status.HTTP_401_UNAUTHORIZED,
-            detail = "Incorrect username or password",
+            detail = "Incorrect password. Run 'unsloth studio reset-password' in your terminal to reset it.",
         )
 
     salt, pwd_hash, _jwt_secret, must_change_password = record
     if not hashing.verify_password(payload.password, salt, pwd_hash):
         raise HTTPException(
             status_code = status.HTTP_401_UNAUTHORIZED,
-            detail = "Incorrect username or password",
+            detail = "Incorrect password. Run 'unsloth studio reset-password' in your terminal to reset it.",
         )
 
     access_token = create_access_token(subject = payload.username)

studio/backend/utils/datasets/llm_assist.py

@@ -26,7 +26,7 @@ from loggers import get_logger
 
 logger = get_logger(__name__)
 
-DEFAULT_HELPER_MODEL_REPO = "unsloth/Qwen3-4B-Instruct-2507-GGUF"
+DEFAULT_HELPER_MODEL_REPO = "unsloth/Qwen3.5-4B-GGUF"
 DEFAULT_HELPER_MODEL_VARIANT = "UD-Q4_K_XL"
 
 README_MAX_CHARS = 1500

studio/frontend/src/features/auth/components/auth-form.tsx

@@ -172,7 +172,7 @@ export function AuthForm({ mode }: AuthFormProps): ReactElement | null {
   const title = isLoginMode ? "Welcome back" : "Setup your account";
   const subtitle = isLoginMode  
     ? "Sign in with your password."
-    : "Choose your new password.";
+    : "Choose a new password";
   const submitLabel = isLoginMode ? "Login" : "Change password";
   const showSwitchLink = !isLoginMode;
   const switchText = "Password already setup? ";