Behaviour when trying to DM a federated user on a server with federation disabled is awful

[ara4n]

Steps to reproduce

1. Logged into the OIDC test lab
2. Tried to DM myself on matrix.org (see also Prompt to set up E2EE on new account didn't happen as expected with OIDC #27437)
3. Got an ambiguous "failed" error in the proto DM.
4. Tried again, which created a new proto DM.
5. Restarted the app
6. Now have two proto-dms in the room list, which provide a 'join' button.
7. Hitting the join button produces a fugly error complaining about trying to call /join on a local+... room ID.

Outcome

What did you expect?

• Reasons why I can't send messages should be shown to the user in the nice red warning error, so the user knows what's going on.
• Failed proto-DMs should be reused when trying to contact the same user
• Failed proto-DMs should not switch to showing a 'join' button which doesn't work, when you refresh

What happened instead?

• The error from the server ({errcode: "M_FORBIDDEN", error: "Federation denied with matrix.org."}) was swallowed entirely by the UI.
• I ended up with multiple broken DMs to the same user
• They ended up giving me useless buggy 'join' buttons

Operating system

No response

Browser information

No response

URL for webapp

https://pr12370--matrix-react-sdk.netlify.app/

Application version

No response

Homeserver

No response

Will you send logs?

No

[t3chguy]

Duplicate of #24991