Fix llama.cpp loading for Unicode Windows profiles

studio/backend/core/inference/llama_cpp.py

@@ -15034,9 +15034,22 @@ def _subset_model_size(n_gpus: int) -> int:
                         # Saved KV encodes chat content; keep it from other local users.
                         with contextlib.suppress(OSError):
                             os.chmod(slot_dir, 0o700)
-                        cmd.extend(["--slot-save-path", str(slot_dir)])
-                        self._slot_save_dir = str(slot_dir)
-                        self._slot_save_binary = (binary, Path(binary).stat().st_mtime_ns)
+                        slot_path = str(slot_dir)
+                        # llama.cpp's fs_is_directory() constructs a narrow
+                        # std::filesystem::path on Windows, so an existing UTF-8
+                        # path such as C:\Users\Егор is rejected as missing.
+                        # Slot persistence is optional; keep model loading available
+                        # until the managed runtime carries the upstream UTF-8 fix.
+                        if sys.platform == "win32" and not slot_path.isascii():
+                            logger.warning(
+                                "Disabling llama.cpp slot persistence because its "
+                                "Windows path contains non-ASCII characters: %s",
+                                slot_path,
+                            )
+                        else:
+                            cmd.extend(["--slot-save-path", slot_path])
+                            self._slot_save_dir = slot_path
+                            self._slot_save_binary = (binary, Path(binary).stat().st_mtime_ns)
                     except OSError:
                         self._slot_save_dir = None
                         self._slot_save_binary = None

studio/backend/tests/test_llama_extra_args_platforms.py

@@ -84,6 +84,48 @@ def _stable(cmd: list[str]) -> list[str]:
     return masked
 
 
+def _launch_with_slot_dir(tmp_path, monkeypatch, platform, slot_dir: Path):
+    """Capture the real launch command with llama.cpp slot persistence advertised."""
+    _apply_platform(monkeypatch, platform)
+    from utils.paths import storage_roots
+
+    monkeypatch.setattr(storage_roots, "llama_slot_cache_root", lambda: slot_dir)
+    backend, gguf = _backend(tmp_path, vulkan = False, memory = [])
+    backend.probe_server_capabilities = lambda _binary = None: {"supports_slot_save": True}
+    return backend, _launch(backend, gguf)["cmd"]
+
+
+def _without_flag_value(cmd: list[str], flag: str) -> list[str]:
+    index = cmd.index(flag)
+    return [*cmd[:index], *cmd[index + 2 :]]
+
+
+def test_windows_unicode_slot_path_only_drops_optional_persistence(tmp_path, monkeypatch):
+    """A/B: all launch arguments survive; only the broken optional pair is absent."""
+    windows = PLATFORMS[2]
+    ascii_dir = tmp_path / "Egor" / "llama-slots"
+    unicode_dir = tmp_path / "Егор" / "llama-slots"
+
+    _ascii_backend, ascii_cmd = _launch_with_slot_dir(tmp_path, monkeypatch, windows, ascii_dir)
+    unicode_backend, unicode_cmd = _launch_with_slot_dir(
+        tmp_path, monkeypatch, windows, unicode_dir
+    )
+
+    assert ascii_cmd[ascii_cmd.index("--slot-save-path") + 1] == str(ascii_dir)
+    assert _stable(unicode_cmd) == _without_flag_value(_stable(ascii_cmd), "--slot-save-path")
+    assert unicode_backend._slot_save_dir is None
+    assert unicode_backend._slot_save_binary is None
+
+
+@pytest.mark.parametrize("platform", [PLATFORMS[0], PLATFORMS[1], PLATFORMS[3]])
+def test_unicode_slot_path_is_unchanged_off_native_windows(tmp_path, monkeypatch, platform):
+    slot_dir = tmp_path / "Егор" / "llama-slots"
+
+    _backend_instance, cmd = _launch_with_slot_dir(tmp_path, monkeypatch, platform, slot_dir)
+
+    assert cmd[cmd.index("--slot-save-path") + 1] == str(slot_dir)
+
+
 @pytest.mark.parametrize("platform,accelerator", MATRIX)
 def test_an_empty_box_changes_nothing_anywhere(tmp_path, monkeypatch, platform, accelerator):
     # The acceptance bar, on every combination. None (inherit) and [] (explicitly