<summary>Attach a file from the user's library to a queued outreach email or LinkedIn message.
Only attach when the user explicitly asks to attach a specific file to someone's
message — never on your own initiative. attachment_id comes from list_attachments.
Name the queued message by exactly one handle: recipient_email for a queued email
(pending or awaiting approval); target_provider_id for a queued LinkedIn message, or
target_identifier for one whose profile is still resolving — both as shown on the row
in manage_linkedin_invite_queue's status read. On LinkedIn only messages carry files,
not connection requests or InMails, and LinkedIn takes fewer file types than email; a
file the channel can't send is refused with the reason. The same file can be attached
to several messages.</summary>
<returns>
<description>The attached file's name and every file now on that message, shaped
`{'attached': True, 'filename', 'attachments': [{'id', 'filename', 'mime_type', 'size'}]}`.</description>
</returns>
ConnectorOAuth