diff --git a/services/api-server/src/api_server/smb_paths.py b/services/api-server/src/api_server/smb_paths.py
index 146c09b..6d5721d 100644
--- a/services/api-server/src/api_server/smb_paths.py
+++ b/services/api-server/src/api_server/smb_paths.py
@@ -77,13 +77,21 @@ def _smbclient() -> Any:
 
 
 def _register_session(smbclient: Any, *, server: str, username: str, password: str, domain: str | None) -> None:
-    qualified_user = f"{domain}\\{username}" if domain else username
-    smbclient.register_session(server, username=qualified_user, password=password)
+    effective_domain, effective_username = _normalize_credentials(username, domain)
+    qualified_user = f"{effective_domain}\\{effective_username}" if effective_domain else effective_username
+    try:
+        smbclient.register_session(server, username=qualified_user, password=password)
+    except Exception as error:  # pragma: no cover - depends on smb backend details
+        raise RuntimeError(_translate_smb_error(error, server=server, username=qualified_user)) from error
 
 
 def _copy_smb_directory(smbclient: Any, source: str, target: Path) -> None:
     target.mkdir(parents=True, exist_ok=True)
-    for item in smbclient.scandir(source):
+    try:
+        items = list(smbclient.scandir(source))
+    except Exception as error:  # pragma: no cover - depends on smb backend details
+        raise RuntimeError(_translate_smb_error(error, path=source)) from error
+    for item in items:
         destination = target / item.name
         child_source = f"{source}\\{item.name}"
         try:
@@ -98,9 +106,12 @@ def _copy_smb_directory(smbclient: Any, source: str, target: Path) -> None:
 
 
 def _copy_local_file_to_smb(smbclient: Any, source: Path, target: str) -> None:
-    with source.open("rb") as local_file:
-        with smbclient.open_file(target, mode="wb") as remote_file:
-            shutil.copyfileobj(local_file, remote_file, length=1024 * 1024)
+    try:
+        with source.open("rb") as local_file:
+            with smbclient.open_file(target, mode="wb") as remote_file:
+                shutil.copyfileobj(local_file, remote_file, length=1024 * 1024)
+    except Exception as error:  # pragma: no cover - depends on smb backend details
+        raise RuntimeError(_translate_smb_error(error, path=target)) from error
 
 
 def _ensure_smb_directory(smbclient: Any, path: str) -> None:
@@ -115,9 +126,9 @@ def _ensure_smb_directory(smbclient: Any, path: str) -> None:
         _ensure_smb_directory(smbclient, parent)
     try:
         smbclient.mkdir(normalized)
-    except OSError:
+    except OSError as error:
         if not smbclient.path.isdir(normalized):
-            raise
+            raise RuntimeError(_translate_smb_error(error, path=normalized)) from error
 
 
 def _unc_parent_path(path: str) -> str | None:
@@ -129,3 +140,31 @@ def _unc_parent_path(path: str) -> str | None:
         return f"\\\\{server}\\{share}"
     parent_relative = "\\".join(parts[:-1])
     return f"\\\\{server}\\{share}\\{parent_relative}"
+
+
+def _normalize_credentials(username: str, domain: str | None) -> tuple[str | None, str]:
+    raw_username = username.strip()
+    raw_domain = (domain or "").strip() or None
+    if "\\" in raw_username:
+        embedded_domain, embedded_username = raw_username.split("\\", 1)
+        return embedded_domain.strip() or raw_domain, embedded_username.strip()
+    if "@" in raw_username and not raw_domain:
+        embedded_username, embedded_domain = raw_username.split("@", 1)
+        return embedded_domain.strip() or None, embedded_username.strip()
+    return raw_domain, raw_username
+
+
+def _translate_smb_error(error: Exception, *, server: str | None = None, path: str | None = None, username: str | None = None) -> str:
+    message = str(error).strip()
+    lowered = message.casefold()
+    target = path or server or "сетевой ресурс"
+    if any(token in lowered for token in ["logon failure", "access denied", "authentication", "STATUS_LOGON_FAILURE".casefold(), "STATUS_ACCESS_DENIED".casefold()]):
+        user_part = f" для пользователя {username}" if username else ""
+        return f"Ошибка авторизации SMB{user_part}. Проверьте логин, пароль, домен и права доступа к {target}."
+    if any(token in lowered for token in ["bad network name", "object name not found", "path not found", "no such file", "STATUS_OBJECT_PATH_NOT_FOUND".casefold(), "STATUS_BAD_NETWORK_NAME".casefold()]):
+        return f"Сетевой путь не найден или недоступен: {target}."
+    if any(token in lowered for token in ["connection reset", "connection refused", "timed out", "host is down", "network name deleted", "network path was not found"]):
+        return f"Не удалось подключиться к сетевому ресурсу {target}. Проверьте доступность сервера и сети."
+    if message:
+        return f"Ошибка SMB при обращении к {target}: {message}"
+    return f"Неизвестная ошибка SMB при обращении к {target}."
diff --git a/services/api-server/tests/test_api.py b/services/api-server/tests/test_api.py
index 7e33b49..076ffd8 100644
--- a/services/api-server/tests/test_api.py
+++ b/services/api-server/tests/test_api.py
@@ -1310,6 +1310,28 @@ def test_server_smb_browse_validates_unc_path():
     assert "UNC путь" in response.json()["error"]
 
 
+def test_smb_credentials_embedded_domain_format_is_normalized():
+    from api_server import smb_paths
+
+    domain, username = smb_paths._normalize_credentials("MST\\m", None)
+
+    assert domain == "MST"
+    assert username == "m"
+
+
+def test_smb_error_translation_returns_russian_auth_message():
+    from api_server import smb_paths
+
+    message = smb_paths._translate_smb_error(
+        RuntimeError("STATUS_LOGON_FAILURE: logon failure"),
+        server="192.168.220.200",
+        username="MST\\m",
+    )
+
+    assert "Ошибка авторизации SMB" in message
+    assert "Проверьте логин, пароль, домен" in message
+
+
 def test_project_setup_recovers_indexed_status_from_stored_snapshot(tmp_path: Path):
     (tmp_path / "metadata.xml").write_text(
         """