Refactor Branch Creation Logic and Update Tests

src/seer/automation/codebase/repo_client.py

@@ -322,18 +322,12 @@ def get_valid_file_paths(self, sha: str | None = None) -> set[str]:
         return valid_file_paths
 
     def _create_branch(self, branch_name):
-        try:
-            ref = self.repo.create_git_ref(
-                ref=f"refs/heads/{branch_name}", sha=self.get_default_branch_head_sha()
-            )
-            return ref
-        except GithubException as e:
-            # if reference already exists (422), just fetch and return it
-            if e.status == 422:
-                return self.repo.get_git_ref(f"heads/{branch_name}")
-            raise e
+        ref = self.repo.create_git_ref(
+            ref=f"refs/heads/{branch_name}", sha=self.get_default_branch_head_sha()
+        )
+        return ref
 
-    def process_one_file_for_git_commit(
+    def create_branch_from_changes(
         self, *, branch_ref: str, patch: FilePatch | None = None, change: FileChange | None = None
     ) -> InputGitTreeElement | None:
         """
@@ -393,8 +387,8 @@ def create_branch_from_changes(
         try:
             branch_ref = self._create_branch(new_branch_name)
         except GithubException as e:
-            # only use the random suffix if the branch already exists
-            if e.status == 409:
+            # Handle both 409 (conflict) and 422 (reference already exists) by generating a new name
+            if e.status in (409, 422):
                 new_branch_name = f"{new_branch_name}/{generate_random_string(n=6)}"
                 branch_ref = self._create_branch(new_branch_name)
             else:

tests/automation/codebase/test_repo_client.py

@@ -446,6 +446,25 @@ def test_create_branch_from_changes_branch_already_exists(
         )
         assert result is not None
         assert mock_create_branch.calls[0].args[0].startswith("autofix/test-pr/")
+
+    @patch("seer.automation.codebase.repo_client.RepoClient._create_branch")
+    def test_create_branch_from_changes_reference_already_exists(
+        self, mock_create_branch, repo_client, mock_github
+    ):
+        mock_github.get_repo.return_value.compare.return_value = MagicMock(ahead_by=1)
+        # First call raises 422, second call succeeds with random suffix
+        mock_create_branch.side_effect = [
+            GithubException(422, "Reference already exists", None),
+            MagicMock(ref="autofix/test-pr/123456")
+        ]
+
+        result = repo_client.create_branch_from_changes(
+            pr_title="autofix/Test PR",
+            file_patches=[next(generate(FileChange))],
+            file_changes=[]
+        )
+        assert result is not None
+        assert mock_create_branch.call_args_list[1][0][0].startswith("autofix/test-pr/")
 
     @pytest.mark.parametrize(
         "input_type,input_data",