fix(py39): replace PEP 604 union types with Optional for Python 3.9 compatibility

- Replaced all `X | None` type hints with `Optional[X]`
- Adjusted typing imports across modules
- Fixed import order and removed invalid future-import placements
- Ensured code runs correctly on Python 3.9

https://chatgpt.com/share/693c58e1-ce70-800f-9088-5864571e024a

src/pkgmgr/actions/branch/close_branch.py

@@ -1,5 +1,4 @@
 from __future__ import annotations
-
 from typing import Optional
 from pkgmgr.core.git import run_git, GitError, get_current_branch
 from .utils import _resolve_base_branch

src/pkgmgr/actions/branch/drop_branch.py

@@ -1,5 +1,4 @@
 from __future__ import annotations
-
 from typing import Optional
 from pkgmgr.core.git import run_git, GitError, get_current_branch
 from .utils import _resolve_base_branch

src/pkgmgr/actions/branch/open_branch.py

@@ -1,5 +1,4 @@
 from __future__ import annotations
-
 from typing import Optional
 from pkgmgr.core.git import run_git, GitError
 from .utils import _resolve_base_branch

src/pkgmgr/actions/install/__init__.py

@@ -15,7 +15,7 @@ Responsibilities:
 from __future__ import annotations
 
 import os
-from typing import Any, Dict, List
+from typing import Any, Dict, List, Optional
 
 from pkgmgr.core.repository.identifier import get_repo_identifier
 from pkgmgr.core.repository.dir import get_repo_dir
@@ -63,7 +63,7 @@ def _ensure_repo_dir(
     no_verification: bool,
     clone_mode: str,
     identifier: str,
-) -> str | None:
+) -> Optional[str]:
     """
     Compute and, if necessary, clone the repository directory.
 

src/pkgmgr/actions/install/capabilities.py

@@ -35,7 +35,7 @@ from __future__ import annotations
 import glob
 import os
 from abc import ABC, abstractmethod
-from typing import Iterable, TYPE_CHECKING
+from typing import Iterable, TYPE_CHECKING, Optional
 
 if TYPE_CHECKING:
     from pkgmgr.actions.install.context import RepoContext
@@ -46,7 +46,7 @@ if TYPE_CHECKING:
 # ---------------------------------------------------------------------------
 
 
-def _read_text_if_exists(path: str) -> str | None:
+def _read_text_if_exists(path: str) -> Optional[str]:
     """Read a file as UTF-8 text, returning None if it does not exist or fails."""
     if not os.path.exists(path):
         return None
@@ -75,7 +75,7 @@ def _scan_files_for_patterns(files: Iterable[str], patterns: Iterable[str]) -> b
     return False
 
 
-def _first_spec_file(repo_dir: str) -> str | None:
+def _first_spec_file(repo_dir: str) -> Optional[str]:
     """Return the first *.spec file in repo_dir, if any."""
     matches = glob.glob(os.path.join(repo_dir, "*.spec"))
     if not matches:
@@ -360,7 +360,7 @@ def detect_capabilities(
 
 def resolve_effective_capabilities(
     ctx: "RepoContext",
-    layers: Iterable[str] | None = None,
+    layers: Optional[Iterable[str]] = None,
 ) -> dict[str, set[str]]:
     """
     Resolve *effective* capabilities for each layer using a bottom-up strategy.

src/pkgmgr/actions/install/installers/base.py

@@ -6,7 +6,7 @@ Base interface for all installer components in the pkgmgr installation pipeline.
 """
 
 from abc import ABC, abstractmethod
-from typing import Set
+from typing import Set, Optional
 
 from pkgmgr.actions.install.context import RepoContext
 from pkgmgr.actions.install.capabilities import CAPABILITY_MATCHERS
@@ -24,7 +24,7 @@ class BaseInstaller(ABC):
     #   Examples: "nix", "python", "makefile".
     #   This is used by capability matchers to decide which patterns to
     #   search for in the repository.
-    layer: str | None = None
+    layer: Optional[str] = None
 
     def discover_capabilities(self, ctx: RepoContext) -> Set[str]:
         """

src/pkgmgr/actions/install/installers/os_packages/debian_control.py

@@ -17,7 +17,7 @@ apt/dpkg tooling are available.
 import glob
 import os
 import shutil
-from typing import List
+from typing import List, Optional
 
 from pkgmgr.actions.install.context import RepoContext
 from pkgmgr.actions.install.installers.base import BaseInstaller
@@ -67,7 +67,7 @@ class DebianControlInstaller(BaseInstaller):
         pattern = os.path.join(parent, "*.deb")
         return sorted(glob.glob(pattern))
 
-    def _privileged_prefix(self) -> str | None:
+    def _privileged_prefix(self) -> Optional[str]:
         """
         Determine how to run privileged commands:
 

src/pkgmgr/actions/mirror/git_remote.py

@@ -1,10 +1,10 @@
 from __future__ import annotations
 
 import os
-from typing import List, Optional, Set
 
 from pkgmgr.core.command.run import run_command
 from pkgmgr.core.git import GitError, run_git
+from typing import List, Optional, Set
 
 from .types import MirrorMap, RepoMirrorContext, Repository
 

src/pkgmgr/actions/release/workflow.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+from typing import Optional
 
 import os
 import sys

src/pkgmgr/cli/commands/changelog.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+from typing import Optional
 
 import os
 import sys

src/pkgmgr/cli/commands/config.py

@@ -7,7 +7,7 @@ import os
 import sys
 import shutil
 from pathlib import Path
-from typing import Any, Dict
+from typing import Any, Dict, Optional
 
 import yaml
 
@@ -36,7 +36,7 @@ def _load_user_config(user_config_path: str) -> Dict[str, Any]:
     return {"repositories": []}
 
 
-def _find_defaults_source_dir() -> str | None:
+def _find_defaults_source_dir() -> Optional[str]:
     """
     Find the directory inside the installed pkgmgr package OR the
     project root that contains default config files.

src/pkgmgr/cli/commands/version.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+from typing import Optional
 
 import os
 import sys

src/pkgmgr/core/command/resolve.py

@@ -1,3 +1,4 @@
+from typing import Optional
 import os
 import shutil
 from typing import Optional, List, Dict, Any

src/pkgmgr/core/command/run.py

@@ -1,3 +1,4 @@
+from typing import Optional
 # pkgmgr/run_command.py
 import subprocess
 import sys

src/pkgmgr/core/config/load.py

@@ -40,7 +40,7 @@ from __future__ import annotations
 
 import os
 from pathlib import Path
-from typing import Any, Dict, List, Tuple
+from typing import Any, Dict, List, Tuple, Optional
 
 import yaml
 
@@ -83,7 +83,7 @@ def _repo_key(repo: Repo) -> Tuple[str, str, str]:
 def _merge_repo_lists(
     base_list: List[Repo],
     new_list: List[Repo],
-    category_name: str | None = None,
+    category_name: Optional[str] = None,
 ) -> List[Repo]:
     """
     Merge two repository lists, matching by (provider, account, repository).
@@ -143,7 +143,7 @@ def _load_yaml_file(path: Path) -> Dict[str, Any]:
 
 def _load_layer_dir(
     config_dir: Path,
-    skip_filename: str | None = None,
+    skip_filename: Optional[str] = None,
 ) -> Dict[str, Any]:
     """
     Load all *.yml/*.yaml from a directory as layered defaults.