As discussed with @benbrandt and @mikayla-maki:

* We now tell ACP clients we support the nonstandard `terminal-auth`
`_meta` field for terminal-based authentication
* In the future, we anticipate ACP itself supporting *some* form of
terminal-based authentication, but that hasn't been designed yet or gone
through the RFD process
* For now, this unblocks terminal-based auth

Release Notes:

- Added experimental terminal-based authentication to ACP support