fix: initialize common directory before config

Capture GIT_COMMON_DIR before the first repository config read so bare-state detection uses the same metadata location as discovery. Resolve relative environment values immediately so later working-directory changes cannot retarget the Repo.

This addresses both substantive review findings on ebe02652. The regression now covers relative common storage, bare config, and use after leaving the construction directory.

Validation: 9 focused tests and 4 subtests; Ruff check/format; mypy; git diff --check.

Author: codex

git/repo/base.py

@@ -356,23 +356,23 @@ def __init__(
             raise InvalidGitRepositoryError(epath)
         self.git_dir = git_dir
 
-        self._bare = False
-        try:
-            self._bare = self.config_reader("repository").getboolean("core", "bare")
-        except Exception:
-            # Let's not assume the option exists, although it should.
-            pass
-
         common_dir = os.getenv("GIT_COMMON_DIR")
         if common_dir is not None:
-            self._common_dir = common_dir
+            self._common_dir = osp.abspath(common_dir)
         else:
             try:
                 common_dir = (Path(self.git_dir) / "commondir").read_text().splitlines()[0].strip()
                 self._common_dir = osp.join(self.git_dir, common_dir)
             except OSError:
                 self._common_dir = ""
 
+        self._bare = False
+        try:
+            self._bare = self.config_reader("repository").getboolean("core", "bare")
+        except Exception:
+            # Let's not assume the option exists, although it should.
+            pass
+
         # Adjust the working directory in case we are actually bare - we didn't know
         # that in the first place.
         if self._bare:

test/test_repo.py

@@ -171,12 +171,15 @@ def test_repo_discovery_uses_git_common_dir(self):
             (git_dir / "HEAD").write_text("ref: refs/heads/main\n")
             (common_dir / "objects").mkdir()
             (common_dir / "refs").mkdir()
+            (common_dir / "config").write_text("[core]\n\tbare = true\n")
 
-            with mock.patch.dict(os.environ, {"GIT_DIR": str(git_dir), "GIT_COMMON_DIR": str(common_dir)}):
-                repo = Repo()
+            with cwd(tdir):
+                with mock.patch.dict(os.environ, {"GIT_DIR": "git", "GIT_COMMON_DIR": "common"}):
+                    repo = Repo()
 
             assert osp.samefile(repo.common_dir, common_dir)
             assert osp.samefile(repo.odb.root_path(), common_dir / "objects")
+            assert repo.bare
 
     @with_rw_repo("0.3.2.1")
     def test_repo_creation_from_different_paths(self, rw_repo):