Make the single instance data type checked

kitty/types.py

@@ -3,7 +3,7 @@
 
 from enum import Enum
 from functools import update_wrapper
-from typing import TYPE_CHECKING, Any, Callable, Dict, Generic, Iterator, NamedTuple, Tuple, TypeVar, Union
+from typing import TYPE_CHECKING, Any, Callable, Dict, Generic, Iterator, Mapping, NamedTuple, Optional, Sequence, Tuple, TypedDict, TypeVar, Union
 
 if TYPE_CHECKING:
     from kitty.fast_data_types import SingleKey
@@ -11,6 +11,16 @@ if TYPE_CHECKING:
 _T = TypeVar('_T')
 
 
+class SingleInstanceData(TypedDict):
+    cmd: str
+    args: Sequence[str]
+    cmdline_args_for_open: Sequence[str]
+    cwd: str
+    session_data: str
+    environ: Mapping[str, str]
+    notify_on_os_window_death: Optional[str]
+
+
 class OverlayType(Enum):
     transient: str = 'transient'
     main: str = 'main'