fix: improve AI cherry-pick conflict resolution for modify/delete conflicts (#1046)

## Summary
- Updated AI conflict resolution prompt with explicit rules for
modify/delete conflicts
- For modify/delete conflicts (file "deleted in HEAD"), the AI now keeps
the file instead of deleting it
- Removed `--allow-empty` fallback — empty cherry-picks now fall back to
manual instructions since they indicate incorrect AI resolution

## Context
Cherry-pick of PR RedHatQE/mtv-api-tests#349 to v2.10 resulted in an
empty PR (#352) because the AI deleted the file (following the old
prompt's "prefer target branch version" instruction). The file
`tools/bm-dns-setup.sh` doesn't exist on v2.10 — git reports this as
"deleted in HEAD" but it's actually a new file being brought to the
target branch.

## Test plan
- [x] Updated `test_cherry_pick_ai_resolves_conflicts` verifies prompt
includes modify/delete guidance
- [x] Updated `test_cherry_pick_ai_empty_result_falls_back_to_manual`
verifies empty cherry-picks fail correctly
- [x] Full test suite passes (1436 tests, 90.28% coverage)

Closes #1043

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Improvements**
* Updated AI conflict-resolution behavior to handle modify/delete
conflicts more explicitly and simplify post-resolution instructions.

* **Bug Fixes**
* Changed empty cherry-pick handling to report failure instead of
creating empty commits or attempting auto-fallbacks.

* **Tests**
* Updated tests to expect a manual fallback path and to verify the AI
prompt includes delete/modify conflict guidance.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: myakove

webhook_server/libs/handlers/runner_handler.py

@@ -745,12 +745,20 @@ async def _resolve_cherry_pick_with_ai(
 
         prompt = (
             "You are in a git repository with cherry-pick merge conflicts. "
-            "The conflicted files contain git conflict markers (<<<<<<< HEAD, =======, >>>>>>>). "
-            "Resolve ALL conflicts in ALL files. "
-            "Priority: the target branch (HEAD/upstream) changes are the baseline. "
-            "Adapt the cherry-picked changes to fit the target branch's codebase. "
-            "If changes are incompatible, prefer the target branch version. "
-            "After resolving, ensure the code compiles/is syntactically valid."
+            "Resolve ALL conflicts in ALL files.\n\n"
+            "How to handle each conflict type:\n"
+            "- Standard conflict markers (<<<<<<< HEAD, =======, >>>>>>>): "
+            "HEAD is the target branch. Adapt the cherry-picked changes to fit "
+            "the target branch code.\n"
+            "- File 'deleted in HEAD and modified in <commit>': This means the file "
+            "does not exist on the target branch. If the cherry-pick is introducing "
+            "this file to the target branch, keep the file and 'git add' it. "
+            "If the file was intentionally removed from the target branch and the "
+            "changes are not relevant, 'git rm' it.\n"
+            "- File 'added in both' or 'renamed': Merge the content, keeping both "
+            "sides' intent.\n\n"
+            "After resolving all conflicts, stage everything with 'git add' and "
+            "make sure the result is syntactically valid."
         )
 
         self.logger.info(f"{self.log_prefix} Attempting AI conflict resolution with {ai_provider}/{ai_model}")
@@ -801,22 +809,8 @@ async def _resolve_cherry_pick_with_ai(
                     mask_sensitive=self.github_webhook.mask_sensitive,
                 )
                 if not rc:
-                    if "cherry-pick is now empty" in err:
-                        self.logger.info(
-                            f"{self.log_prefix} Cherry-pick is empty after AI resolution, committing with --allow-empty"
-                        )
-                        rc_empty, _, err_empty = await run_command(
-                            command=f"{git_cmd} -c core.editor=true commit --allow-empty -C CHERRY_PICK_HEAD",
-                            log_prefix=self.log_prefix,
-                            redact_secrets=[github_token],
-                            mask_sensitive=self.github_webhook.mask_sensitive,
-                        )
-                        if not rc_empty:
-                            self.logger.error(f"{self.log_prefix} Failed to commit empty cherry-pick: {err_empty}")
-                            return False
-                    else:
-                        self.logger.error(f"{self.log_prefix} cherry-pick --continue failed after AI resolution: {err}")
-                        return False
+                    self.logger.error(f"{self.log_prefix} cherry-pick --continue failed after AI resolution: {err}")
+                    return False
             else:
                 if err_check and "needed a single revision" not in err_check.lower():
                     self.logger.error(f"{self.log_prefix} Unexpected CHERRY_PICK_HEAD check error: {err_check}")

webhook_server/tests/test_runner_handler.py

@@ -1502,6 +1502,11 @@ async def run_command_side_effect(command: str, **kwargs: Any) -> tuple[bool, st
                                         await runner_handler.cherry_pick(mock_pull_request, "main")
                                         mock_set_success.assert_called_once()
                                         mock_ai_cli.assert_called_once()
+                                        # Verify prompt includes delete/modify conflict guidance
+                                        ai_prompt = str(mock_ai_cli.call_args)
+                                        assert "deleted in HEAD and modified in" in ai_prompt, (
+                                            "AI prompt should include delete/modify conflict guidance"
+                                        )
                                         # Verify AI comment was posted
                                         comment_calls = mock_pull_request.create_issue_comment.call_args_list
                                         ai_comment = any(
@@ -1599,10 +1604,10 @@ async def run_command_side_effect(command: str, **kwargs: Any) -> tuple[bool, st
                                         assert "ai-resolved-conflicts" in gh_cmd_str
 
     @pytest.mark.asyncio
-    async def test_cherry_pick_ai_resolves_empty_cherry_pick(
+    async def test_cherry_pick_ai_empty_result_falls_back_to_manual(
         self, runner_handler: RunnerHandler, mock_pull_request: Mock
     ) -> None:
-        """Cherry-pick conflict resolved by AI results in empty commit — committed with --allow-empty."""
+        """Cherry-pick conflict resolved by AI but result is empty — falls back to manual instructions."""
         runner_handler.github_webhook.ai_features = {
             "ai-provider": "claude",
             "ai-model": "sonnet",
@@ -1624,13 +1629,11 @@ async def run_command_side_effect(command: str, **kwargs: Any) -> tuple[bool, st
                     "The previous cherry-pick is now empty, possibly due to conflict resolution.\n"
                     "If you wish to commit it anyway, use:\n\n    git commit --allow-empty\n",
                 )
-            if "gh pr create" in command:
-                return (True, "https://github.com/test-org/test-repo/pull/99", "")
             return (True, "success", "")
 
         with patch.object(runner_handler, "is_branch_exists", new=AsyncMock(return_value=Mock())):
             with patch.object(runner_handler.check_run_handler, "set_check_in_progress"):
-                with patch.object(runner_handler.check_run_handler, "set_check_success") as mock_set_success:
+                with patch.object(runner_handler.check_run_handler, "set_check_failure") as mock_set_failure:
                     with patch.object(runner_handler, "_checkout_worktree") as mock_checkout:
                         mock_checkout.return_value = AsyncMock()
                         mock_checkout.return_value.__aenter__ = AsyncMock(
@@ -1654,29 +1657,21 @@ async def run_command_side_effect(command: str, **kwargs: Any) -> tuple[bool, st
                                         return_value=None,
                                     ):
                                         await runner_handler.cherry_pick(mock_pull_request, "main")
-                                        mock_set_success.assert_called_once()
+                                        mock_set_failure.assert_called()
                                         mock_ai_cli.assert_called_once()
-                                        # Verify --allow-empty commit was called
+                                        # Verify --allow-empty was NOT called
                                         allow_empty_calls = [
                                             c for c in mock_run_cmd.call_args_list if "commit --allow-empty" in str(c)
                                         ]
-                                        assert allow_empty_calls, (
-                                            "git commit --allow-empty should be called for empty cherry-pick"
-                                        )
-                                        # Verify AI comment was posted
+                                        assert not allow_empty_calls, "git commit --allow-empty should NOT be called"
+                                        # Verify manual cherry-pick comment was posted
                                         comment_calls = mock_pull_request.create_issue_comment.call_args_list
-                                        ai_comment = any(
-                                            "Cherry-pick conflicts were resolved by AI" in str(c) for c in comment_calls
+                                        manual_comment = any(
+                                            "Manual cherry-pick is needed" in str(c) for c in comment_calls
+                                        )
+                                        assert manual_comment, (
+                                            f"Expected manual cherry-pick comment, got: {comment_calls}"
                                         )
-                                        assert ai_comment, f"Expected AI comment, got: {comment_calls}"
-                                        # Verify labels are in gh pr create command
-                                        gh_cmd_calls = [
-                                            c for c in mock_run_cmd.call_args_list if "gh pr create" in str(c)
-                                        ]
-                                        assert gh_cmd_calls, "gh pr create not called"
-                                        gh_cmd_str = str(gh_cmd_calls[-1])
-                                        assert "--label" in gh_cmd_str
-                                        assert "ai-resolved-conflicts" in gh_cmd_str
 
     @pytest.mark.asyncio
     async def test_cherry_pick_ai_fails_fallback(self, runner_handler: RunnerHandler, mock_pull_request: Mock) -> None: