Check capabilities on certain methods

For example:

```python
@requires_capability("attachments")
@retry_timeout
def add_attachment(...):
....
```

Start by locating the client methods that correspond to the example, especially add_attachment, and read how decorators such as retry_timeout are currently applied. Determine which methods need capability checks and what the expected behavior is when a capability is unavailable. Done means the selected methods consistently enforce the required capabilities and the behavior is covered by tests.

Written by the indexing model from the issue text.