From 789666effaa54ca9c2636ff71084a51ab5265f5c Mon Sep 17 00:00:00 2001
From: Herbert Damker <52109189+hdamker@users.noreply.github.com>
Date: Fri, 23 Oct 2026 22:37:50 +0200
Subject: [PATCH] fix(ra): treat a missing ref as absent when deleting a branch

GitHub answers a DELETE on a nonexistent ref with 422 "Reference does not exist", not 404. The first discard of a snapshot id therefore failed to rename the review branch to -preserved.
---
 release_automation/scripts/github_client.py    |  3 ++-
 release_automation/tests/test_github_client.py | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/release_automation/scripts/github_client.py b/release_automation/scripts/github_client.py
index d330666..a5b7d99 100644
--- a/release_automation/scripts/github_client.py
+++ b/release_automation/scripts/github_client.py
@@ -1173,7 +1173,8 @@ def delete_branch(self, branch_name: str) -> bool:
             return True
         except GitHubClientError as e:
             error_msg = str(e).lower()
-            if "404" in error_msg or "not found" in error_msg:
+            # A DELETE on a missing ref answers 422 "Reference does not exist", not 404
+            if "404" in error_msg or "not found" in error_msg or "reference does not exist" in error_msg:
                 return False
             raise
 
diff --git a/release_automation/tests/test_github_client.py b/release_automation/tests/test_github_client.py
index 7f1a524..5a16b6b 100644
--- a/release_automation/tests/test_github_client.py
+++ b/release_automation/tests/test_github_client.py
@@ -69,6 +69,22 @@ def test_list_branches(self, mock_run_gh):
         self.assertEqual(branches[1].name, "branch2")
         self.assertEqual(branches[1].sha, "sha2")
 
+    @patch("release_automation.scripts.github_client.GitHubClient._run_gh")
+    def test_delete_branch(self, mock_run_gh):
+        mock_run_gh.return_value = ""
+        self.assertTrue(self.client.delete_branch("feature"))
+
+        # GitHub answers a DELETE on a missing ref with 422, not 404
+        mock_run_gh.side_effect = GitHubClientError("gh: Reference does not exist (HTTP 422)")
+        self.assertFalse(self.client.delete_branch("missing"))
+
+        mock_run_gh.side_effect = GitHubClientError("gh: Not Found (HTTP 404)")
+        self.assertFalse(self.client.delete_branch("missing"))
+
+        mock_run_gh.side_effect = GitHubClientError("gh: Resource not accessible by integration (HTTP 403)")
+        with self.assertRaises(GitHubClientError):
+            self.client.delete_branch("protected")
+
     @patch("release_automation.scripts.github_client.GitHubClient._run_gh")
     def test_get_file_content(self, mock_run_gh):
         mock_run_gh.return_value = "file content"