# Using hasattr() for entity-type dispatch is banned

### 17.4 Banned: `hasattr()` for entity type dispatch

```python
# BANNED:
def handle_event(self, event: Metadata) -> None:
 if hasattr(event, 'tool_calls'):
  # tool call path
 elif hasattr(event, 'source_tier'):
  # mma path
 elif hasattr(event, 'path'):
  # file path

# CORRECT (typed Union dispatch):
def handle_event(self, event: CommsLogEntry | FileItem | HistoryMessage) -> None:
 if isinstance(event, CommsLogEntry):
  # mma path
 elif isinstance(event, FileItem):
  # file path
 elif isinstance(event, HistoryMessage):
  # tool call path

# CORRECT (preferred — refactor so no dispatch is needed):
def _handle_comms_entry(self, event: CommsLogEntry) -> None: ...
def _handle_file_item(self, event: FileItem) -> None: ...
def _handle_history(self, event: HistoryMessage) -> None: ...
```