studio: tighten sys.prefix inference + Tauri env handling + llama.cpp env

Cycle 3 reviewer.py findings (3 P1s converging):

* sys.prefix inference too broad: a developer venv named 'unsloth_studio'
  was being treated as a custom Studio root. Narrow with an installer-
  sentinel check (presence of share/studio.conf or bin/unsloth shim
  inside the parent dir) in both unsloth_cli/commands/studio.py and
  studio/backend/utils/paths/storage_roots.py.

* Tauri studio/src-tauri/src/process.rs::find_unsloth_binary() hardcoded
  ~/.unsloth/studio. Honor UNSLOTH_STUDIO_HOME / STUDIO_HOME (in that
  priority order) before falling back to legacy.

* unsloth-zoo's GGUF export binds LLAMA_CPP_DEFAULT_DIR at import time
  from UNSLOTH_LLAMA_CPP_PATH. For env-override installs, persist
  UNSLOTH_LLAMA_CPP_PATH alongside UNSLOTH_STUDIO_HOME in studio.conf
  (Unix), in the generated PowerShell launcher (Windows), and via
  os.environ.setdefault in the Python CLI when running on a custom
  root, so GGUF export uses the custom-root llama.cpp build instead
  of the legacy ~/.unsloth/llama.cpp.

Default behaviour unchanged: no env vars are written to studio.conf
in default mode, no LLAMA_CPP_PATH is set, and the dev-venv inference
falls through to legacy when no installer sentinels are present.

install.ps1

@@ -423,7 +423,8 @@ function Install-UnslothStudio {
             # empty string here so behavior matches today exactly.
             $studioHomeExport = if ($StudioRedirectMode -eq 'env') {
                 $_sq = $StudioHome -replace "'", "''"
-                "`$env:UNSLOTH_STUDIO_HOME = '$_sq'`n"
+                $_llama = (Join-Path $StudioHome "llama.cpp") -replace "'", "''"
+                "`$env:UNSLOTH_STUDIO_HOME = '$_sq'`n`$env:UNSLOTH_LLAMA_CPP_PATH = '$_llama'`n"
             } else { "" }
 
             $launcherContent = @"

install.sh

@@ -606,11 +606,15 @@ LAUNCHER_EOF
         printf '%s\n' "UNSLOTH_EXE='$_css_quoted_exe'"
         # Persist UNSLOTH_STUDIO_HOME for env-override installs so the launcher,
         # CLI, and backend pick up the same root in fresh shells where the user
-        # did not re-export the env var. Default installs do NOT get this line so
-        # the legacy ~/.unsloth/studio resolution is fully preserved.
+        # did not re-export the env var. Also persist UNSLOTH_LLAMA_CPP_PATH so
+        # unsloth-zoo's import-time LLAMA_CPP_DEFAULT_DIR binding finds the
+        # custom-root build. Default installs do NOT get these lines so the
+        # legacy ~/.unsloth/studio + ~/.unsloth/llama.cpp resolution stands.
         if [ "$_STUDIO_HOME_REDIRECT" = "env" ]; then
             _css_quoted_home=$(printf '%s' "$STUDIO_HOME" | sed "s/'/'\\\\''/g")
+            _css_quoted_llama=$(printf '%s' "$STUDIO_HOME/llama.cpp" | 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
     } > "$_css_data_dir/studio.conf"
 

studio/backend/utils/paths/storage_roots.py

@@ -11,17 +11,25 @@ import tempfile
 
 
 def _infer_studio_home_from_venv() -> Path | None:
-    """If running from the unsloth_studio venv, the parent dir is STUDIO_HOME.
+    """If running from an installer-managed unsloth_studio venv, return the
+    parent dir as STUDIO_HOME.
 
     Fallback for fresh shells after a custom install where the installer
     wrote to a workspace path but the user did not re-export the env var.
+    Narrowed via installer-sentinel check (share/studio.conf or bin shim)
+    so a developer venv that happens to be named ``unsloth_studio`` is not
+    misidentified as a custom Studio root.
     """
     try:
         prefix = Path(sys.prefix).resolve()
     except (OSError, ValueError):
         return None
-    if prefix.name == "unsloth_studio":
-        return prefix.parent
+    if prefix.name != "unsloth_studio":
+        return None
+    candidate = prefix.parent
+    shim_name = "unsloth.exe" if os.name == "nt" else "unsloth"
+    if (candidate / "share" / "studio.conf").is_file() or (candidate / "bin" / shim_name).exists():
+        return candidate
     return None
 
 

studio/src-tauri/src/process.rs

@@ -111,9 +111,22 @@ fn find_unsloth_binary_in_studio_dir(studio: &std::path::Path) -> Option<std::pa
 }
 
 pub fn find_unsloth_binary() -> Option<std::path::PathBuf> {
+    // Honor UNSLOTH_STUDIO_HOME / STUDIO_HOME (in that priority order) so
+    // Tauri custom-root installs can locate the venv. Falls back to the
+    // legacy ~/.unsloth/studio when neither is set.
+    for var in ["UNSLOTH_STUDIO_HOME", "STUDIO_HOME"] {
+        if let Some(value) = std::env::var_os(var) {
+            if !value.is_empty() {
+                let studio = std::path::PathBuf::from(value);
+                if let Some(bin) = find_unsloth_binary_in_studio_dir(&studio) {
+                    return Some(bin);
+                }
+            }
+        }
+    }
+
     let home = dirs::home_dir()?;
     let studio = home.join(".unsloth").join("studio");
-
     find_unsloth_binary_in_studio_dir(&studio)
 }
 

unsloth_cli/commands/studio.py

@@ -28,6 +28,18 @@ studio_app = typer.Typer(help = "Unsloth Studio commands.")
 # Returns (path, is_custom): is_custom=True only when the resolved root is a
 # real override; we use this to decide whether to re-export the env var to
 # child processes.
+def _looks_like_installer_managed_studio_home(candidate: Path) -> bool:
+    """Heuristic: only treat a directory as an installer-managed Studio root
+    if it carries installer-written sentinels (studio.conf or the bin shim).
+    Avoids over-matching on a dev venv that happens to be named unsloth_studio.
+    """
+    shim_name = "unsloth.exe" if platform.system() == "Windows" else "unsloth"
+    return (
+        (candidate / "share" / "studio.conf").is_file()
+        or (candidate / "bin" / shim_name).exists()
+    )
+
+
 def _resolve_studio_home() -> tuple[Path, bool]:
     override = os.environ.get("UNSLOTH_STUDIO_HOME") or os.environ.get("STUDIO_HOME")
     if override:
@@ -37,7 +49,8 @@ def _resolve_studio_home() -> tuple[Path, bool]:
         if prefix.name == "unsloth_studio":
             inferred = prefix.parent
             legacy = (Path.home() / ".unsloth" / "studio").resolve()
-            return inferred, inferred != legacy
+            if inferred != legacy and _looks_like_installer_managed_studio_home(inferred):
+                return inferred, True
     except (OSError, ValueError):
         pass
     return Path.home() / ".unsloth" / "studio", False
@@ -48,8 +61,12 @@ STUDIO_HOME, _STUDIO_HOME_IS_CUSTOM = _resolve_studio_home()
 # backend run.py) inherit it. Default installs MUST NOT re-export the env
 # var, because setup.sh / setup.ps1 treat its presence as "env-override
 # mode" and would relocate llama.cpp / DATA_DIR away from legacy paths.
+# UNSLOTH_LLAMA_CPP_PATH is also setdefault for custom roots so
+# unsloth-zoo's import-time LLAMA_CPP_DEFAULT_DIR binding picks up the
+# 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"))
 BOOTSTRAP_PASSWORD_FILE = ".bootstrap_password"
 DESKTOP_SECRET_FILE = ".desktop_secret"
 DEFAULT_ADMIN_USERNAME = "unsloth"