studio: desktop_auth env-aware + legacy-root llama.cpp consistency

- desktop_auth.rs: honor UNSLOTH_STUDIO_HOME / STUDIO_HOME for the
  .desktop_secret path so Tauri desktop login works against custom-root
  installs instead of always reading ~/.unsloth/studio/auth/.

- install.sh / install.ps1 / unsloth_cli/commands/studio.py: when an env
  override resolves to the legacy default ($HOME/.unsloth/studio), set
  UNSLOTH_LLAMA_CPP_PATH to ~/.unsloth/llama.cpp (matching setup.sh /
  setup.ps1's legacy-equality branch). Previously the persisted value
  pointed at $STUDIO_HOME/llama.cpp, which was a non-existent location
  and broke unsloth-zoo's import-time GGUF binding for that edge case.

install.ps1

@@ -422,8 +422,17 @@ function Install-UnslothStudio {
             # the user re-exporting the env var. Default installs get an
             # empty string here so behavior matches today exactly.
             $studioHomeExport = if ($StudioRedirectMode -eq 'env') {
+                # Mirror setup.ps1: when an env override happens to equal the
+                # legacy default, llama.cpp still lives at ~/.unsloth/llama.cpp.
+                # Keep the persisted UNSLOTH_LLAMA_CPP_PATH consistent with that.
+                $_legacyStudio = Join-Path $env:USERPROFILE ".unsloth\studio"
+                $_llamaPath = if ($StudioHome -eq $_legacyStudio) {
+                    Join-Path $env:USERPROFILE ".unsloth\llama.cpp"
+                } else {
+                    Join-Path $StudioHome "llama.cpp"
+                }
                 $_sq = $StudioHome -replace "'", "''"
-                $_llama = (Join-Path $StudioHome "llama.cpp") -replace "'", "''"
+                $_llama = $_llamaPath -replace "'", "''"
                 "`$env:UNSLOTH_STUDIO_HOME = '$_sq'`n`$env:UNSLOTH_LLAMA_CPP_PATH = '$_llama'`n"
             } else { "" }
 

install.sh

@@ -611,8 +611,18 @@ LAUNCHER_EOF
         # custom-root build. Default installs do NOT get these lines so the
         # legacy ~/.unsloth/studio + ~/.unsloth/llama.cpp resolution stands.
         if [ "$_STUDIO_HOME_REDIRECT" = "env" ]; then
+            # Mirror setup.sh's legacy-equality check: when an env override
+            # happens to point at the legacy default, llama.cpp still lives
+            # at ~/.unsloth/llama.cpp (one shared build across legacy
+            # installs) -- keep UNSLOTH_LLAMA_CPP_PATH consistent with that.
+            _css_legacy_studio="$HOME/.unsloth/studio"
+            if [ "$STUDIO_HOME" = "$_css_legacy_studio" ]; then
+                _css_llama_path="$HOME/.unsloth/llama.cpp"
+            else
+                _css_llama_path="$STUDIO_HOME/llama.cpp"
+            fi
             _css_quoted_home=$(printf '%s' "$STUDIO_HOME" | sed "s/'/'\\\\''/g")
-            _css_quoted_llama=$(printf '%s' "$STUDIO_HOME/llama.cpp" | sed "s/'/'\\\\''/g")
+            _css_quoted_llama=$(printf '%s' "$_css_llama_path" | sed "s/'/'\\\\''/g")
             printf '%s\n' "export UNSLOTH_STUDIO_HOME='$_css_quoted_home'"
             printf '%s\n' "export UNSLOTH_LLAMA_CPP_PATH='$_css_quoted_llama'"
         fi

studio/src-tauri/src/desktop_auth.rs

@@ -57,6 +57,10 @@ fn auth_secret_path(home: &Path, filename: &str) -> PathBuf {
         .join(filename)
 }
 
+fn auth_secret_path_in_studio(studio: &Path, filename: &str) -> PathBuf {
+    studio.join("auth").join(filename)
+}
+
 fn auth_url(port: u16, route: &str) -> String {
     format!("http://127.0.0.1:{port}/api/auth/{route}")
 }
@@ -65,7 +69,21 @@ fn home_dir() -> Result<PathBuf, String> {
     dirs::home_dir().ok_or_else(|| "Could not determine home directory".to_string())
 }
 
+fn studio_root_from_env() -> Option<PathBuf> {
+    for var in ["UNSLOTH_STUDIO_HOME", "STUDIO_HOME"] {
+        if let Some(value) = std::env::var_os(var) {
+            if !value.is_empty() {
+                return Some(PathBuf::from(value));
+            }
+        }
+    }
+    None
+}
+
 fn desktop_secret_path() -> Result<PathBuf, String> {
+    if let Some(studio) = studio_root_from_env() {
+        return Ok(auth_secret_path_in_studio(&studio, ".desktop_secret"));
+    }
     Ok(auth_secret_path(&home_dir()?, ".desktop_secret"))
 }
 
@@ -308,6 +326,15 @@ mod tests {
         );
     }
 
+    #[test]
+    fn auth_secret_path_in_studio_joins_under_custom_root() {
+        let studio = PathBuf::from("/srv/ws/studio");
+        assert_eq!(
+            auth_secret_path_in_studio(&studio, ".desktop_secret"),
+            PathBuf::from("/srv/ws/studio/auth/.desktop_secret")
+        );
+    }
+
     #[test]
     fn auth_url_builds_local_endpoint() {
         assert_eq!(

unsloth_cli/commands/studio.py

@@ -67,7 +67,15 @@ STUDIO_HOME, _STUDIO_HOME_IS_CUSTOM = _resolve_studio_home()
 # correct build dir for GGUF export.
 if _STUDIO_HOME_IS_CUSTOM:
     os.environ.setdefault("UNSLOTH_STUDIO_HOME", str(STUDIO_HOME))
-    os.environ.setdefault("UNSLOTH_LLAMA_CPP_PATH", str(STUDIO_HOME / "llama.cpp"))
+    # Mirror setup.sh / setup.ps1's legacy-equality check: when an env
+    # override happens to equal the legacy default, llama.cpp still lives
+    # at ~/.unsloth/llama.cpp (one shared build across legacy installs).
+    _legacy_studio = (Path.home() / ".unsloth" / "studio").resolve()
+    if STUDIO_HOME.resolve() == _legacy_studio:
+        _llama_dir = Path.home() / ".unsloth" / "llama.cpp"
+    else:
+        _llama_dir = STUDIO_HOME / "llama.cpp"
+    os.environ.setdefault("UNSLOTH_LLAMA_CPP_PATH", str(_llama_dir))
 BOOTSTRAP_PASSWORD_FILE = ".bootstrap_password"
 DESKTOP_SECRET_FILE = ".desktop_secret"
 DEFAULT_ADMIN_USERNAME = "unsloth"