feat(release): auto-add RC task in process-backports when adding PRs

- Modify `process_backports.py` to check if a pending RC task exists when backports are added.
- If no pending RC task exists, auto-add the next `Tag RC<N>` task to the checklist.
- Add `test_process_backports_add_backports_and_auto_add_rc_task` to `process_backports_test.py` to verify this behavior.

Author: rickeylev

tests/tools/private/release/process_backports_test.py

@@ -247,6 +247,64 @@ def mock_resolve(items):
         self.mock_git.commit.assert_not_called()
         self.mock_git.push.assert_not_called()
 
+    @patch("tools.private.release.process_backports.datetime")
+    def test_process_backports_add_backports_and_auto_add_rc_task(self, mock_datetime):
+        mock_datetime.date.today.return_value = datetime.date(2026, 7, 1)
+        args = argparse.Namespace(
+            issue=123,
+            remote="origin",
+            dry_run=False,
+            add=[124],
+            triggering_comment=None,
+        )
+        self.mock_gh.get_issue_title.return_value = "Release 2.0.0"
+        self.mock_gh.get_issue_body.return_value = """
+## Checklist
+- [x] Prepare Release | status=done pr=#122 commit=abcdef12
+- [x] Create Release branch | status=done branch=release/2.0 commit=abcdef12
+- [x] Tag RC0 | status=done tag=2.0.0-rc0 commit=abcdef12
+- [ ] Tag Final
+
+## Backports
+"""
+        self.mock_git.get_remote_tags.return_value = ["2.0.0-rc0"]
+        self.mock_git.get_commit_sha.return_value = "12345678"
+        self.mock_git.get_commit_message.return_value = 'Cherry-pick "fix bug"'
+
+        def mock_resolve(items):
+            for item in items:
+                if item.pr_ref == "#124":
+                    item.commit = "abcdef12"
+                    item.status = "done"
+            return items
+
+        self.mock_gh.get_merge_commits_for_prs.side_effect = mock_resolve
+        self.mock_git.sort_commits_chronologically.return_value = ["abcdef12"]
+
+        result = ProcessBackports(args, self.mock_git, self.mock_gh).run()
+
+        self.assertEqual(result, 0)
+
+        # update_issue_body should be called twice:
+        # 1. When adding backports and auto-adding Tag RC1 task.
+        # 2. When updating the backport status to done.
+        self.assertEqual(self.mock_gh.update_issue_body.call_count, 2)
+
+        call1_args = self.mock_gh.update_issue_body.call_args_list[0][0]
+        call2_args = self.mock_gh.update_issue_body.call_args_list[1][0]
+
+        self.assertEqual(call1_args[0], 123)
+        self.assertIn("- [ ] #124", call1_args[1])
+        self.assertIn("- [ ] Tag RC1", call1_args[1])
+        self.assertIn(
+            "- [x] Tag RC0 | status=done tag=2.0.0-rc0 commit=abcdef12\n- [ ]"
+            " Tag RC1\n- [ ] Tag Final",
+            call1_args[1].strip(),
+        )
+
+        self.assertEqual(call2_args[0], 123)
+        self.assertIn("- [x] #124 | status=done rc=rc1 commit= 12345678", call2_args[1])
+
 
 if __name__ == "__main__":
     unittest.main()

tools/private/release/process_backports.py

@@ -10,7 +10,9 @@
 from tools.private.release.release_issue import (
     RELEASE_TITLE_RE,
     add_backports_to_body,
+    add_rc_task_to_body,
     parse_backports,
+    parse_checklist_state,
     update_task_in_body,
 )
 from tools.private.release.utils import (
@@ -207,6 +209,19 @@ def _run_internal(self) -> int:
             print(f"Adding backports {args.add} to tracking issue #{args.issue}...")
             try:
                 body = add_backports_to_body(body, args.add)
+                state = parse_checklist_state(body)
+                rc_tags = state.get("rc_tags", {})
+                has_pending_rc = any(
+                    not task.checked and task.status != "done"
+                    for task in rc_tags.values()
+                )
+                next_rc_num = max(rc_tags.keys()) + 1 if rc_tags else 0
+                if not has_pending_rc:
+                    print(
+                        f"No pending RC task found. Adding 'Tag"
+                        f" RC{next_rc_num}' to checklist..."
+                    )
+                    body = add_rc_task_to_body(body, next_rc_num)
             except ValueError as e:
                 print(f"Error: {e}")
                 return 1
@@ -219,6 +234,8 @@ def _run_internal(self) -> int:
                     "[DRY RUN] Would update tracking issue checklist with new"
                     " backports."
                 )
+                if not has_pending_rc:
+                    print(f"[DRY RUN] Would add 'Tag RC{next_rc_num}' to checklist.")
 
         items = parse_backports(body)