Uploader can't see attached files when using chat API

I run this:

```
echo '{"method": "attach", "params": {"version": 1, "options": {"channel": {"name": "", "members_type": "team", "topic_name": "general"}, "filename": "/keybase/team//gifs/this_guy.jpg", "title": "TEST"}}}' | keybase chat api
```

My teammates see the first, I see the second. Reproduced in reverse too, where they were the uploader and I could not see.


my log id: ba837bedf33cd5e3ac0bed1c

Start with the `keybase chat api` entry point and the `attach` method using the reproduction command in the issue. Compare visibility for the uploader and teammates, then trace the attachment handling until the failure is located. Done means all channel members can see files uploaded through the chat API.

Written by the indexing model from the issue text.