CG-17442: Fix DoubleReactException by handling already_reacted Slack API errors

src/codegen/extensions/slack/utils/README.md

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+# Slack Utilities
+
+This module provides utility functions for working with the Slack API in a safe and reliable way.
+
+## Features
+
+### `safe_add_reaction`
+
+A utility function that safely adds a reaction to a Slack message, handling the case where the reaction already exists.
+
+This function is particularly useful for preventing the `SlackApiError` with the error message `already_reacted` that can occur when trying to add a reaction that already exists on a message.
+
+### Usage
+
+```python
+from slack_sdk import WebClient
+from codegen.extensions.slack.utils import safe_add_reaction
+
+client = WebClient(token="your-token")
+
+# Safely add a reaction
+response = safe_add_reaction(client=client, channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+# The function will not raise an exception if the reaction already exists
+```
+
+## Error Handling
+
+The `safe_add_reaction` function handles the following error cases:
+
+- If the reaction already exists (`already_reacted` error), it logs the information and returns a success response.
+- For all other errors, it logs the error and re-raises the exception for proper handling upstream.

src/codegen/extensions/slack/utils/__init__.py

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+"""Utility functions for Slack integration."""
+
+import logging
+from typing import Any, Dict, Optional
+
+from slack_sdk import WebClient
+from slack_sdk.errors import SlackApiError
+
+from codegen.shared.logging.get_logger import get_logger
+
+logger = get_logger(__name__)
+logger.setLevel(logging.INFO)
+
+
+def safe_add_reaction(
+    client: WebClient,
+    channel: str,
+    timestamp: str,
+    name: str,
+) -> dict[str, Any]:
+    """Safely add a reaction to a Slack message, handling the case where the reaction already exists.
+
+    Args:
+        client: The Slack WebClient instance
+        channel: The channel ID where the message is located
+        timestamp: The timestamp of the message
+        name: The name of the reaction emoji to add
+
+    Returns:
+        The response from the Slack API or an error response
+    """
+    try:
+        return client.reactions_add(
+            channel=channel,
+            timestamp=timestamp,
+            name=name,
+        )
+    except SlackApiError as e:
+        # If the error is "already_reacted", just log it and continue
+        if e.response["error"] == "already_reacted":
+            logger.info(f"Reaction '{name}' already exists on message in channel {channel} at {timestamp}. Ignoring.")
+            # Return a success response to prevent further error handling
+            return {"ok": True, "already_exists": True}
+        # For other errors, re-raise
+        logger.exception(f"Error adding reaction: {e}")
+        raise

tests/unit/codegen/extensions/slack/utils/test_utils.py

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+"""Tests for Slack utility functions."""
+
+from unittest.mock import MagicMock
+
+import pytest
+from slack_sdk import WebClient
+from slack_sdk.errors import SlackApiError
+
+from codegen.extensions.slack.utils import safe_add_reaction
+
+
+def test_safe_add_reaction_success():
+    """Test that safe_add_reaction works correctly when the API call succeeds."""
+    mock_client = MagicMock(spec=WebClient)
+    mock_client.reactions_add.return_value = {"ok": True}
+
+    result = safe_add_reaction(client=mock_client, channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+    assert result == {"ok": True}
+    mock_client.reactions_add.assert_called_once_with(channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+
+def test_safe_add_reaction_already_reacted():
+    """Test that safe_add_reaction handles the 'already_reacted' error correctly."""
+    mock_client = MagicMock(spec=WebClient)
+
+    # Create a mock SlackApiError with the 'already_reacted' error
+    mock_response = {"ok": False, "error": "already_reacted"}
+    mock_error = SlackApiError(message="already_reacted", response=mock_response)
+    mock_client.reactions_add.side_effect = mock_error
+
+    result = safe_add_reaction(client=mock_client, channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+    # Should return a success response with already_exists=True
+    assert result == {"ok": True, "already_exists": True}
+    mock_client.reactions_add.assert_called_once_with(channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+
+def test_safe_add_reaction_other_error():
+    """Test that safe_add_reaction re-raises other errors."""
+    mock_client = MagicMock(spec=WebClient)
+
+    # Create a mock SlackApiError with a different error
+    mock_response = {"ok": False, "error": "invalid_auth"}
+    mock_error = SlackApiError(message="invalid_auth", response=mock_response)
+    mock_client.reactions_add.side_effect = mock_error
+
+    with pytest.raises(SlackApiError):
+        safe_add_reaction(client=mock_client, channel="C12345", timestamp="1234567890.123456", name="thumbsup")
+
+    mock_client.reactions_add.assert_called_once_with(channel="C12345", timestamp="1234567890.123456", name="thumbsup")