Connection fails when deploying, but works outside of morph

Sorry if this is the wrong place to ask this.

I am having an issue deploying to a server using morph.

I am connecting to a server using SSH authentication with ECDSA and password authentication disabled. Since upgrading morph and Nix (for the first time in a long time) I have noticed this problem:

[nix-shell:~/src/infra]$ ssh root@r4.local -- uptime
 15:30:40  up 32 days 22:58,  1 user,  load average: 0.08, 0.02, 0.01

(Connecting to the host through SSH with ECDSA auth works in the same shell I'm running morph in.)

But when I try to deploy, I get this error:

[nix-shell:~/src/infra]$ morph deploy network.nix --on=r4 test

[...snip...]
Pushing paths to r4 (root@r4.local):
    * /nix/store/lf7hfid23wxhsvm9dxscq3v4nx5lxhrx-nixos-system-r4-24.05pre552293.5a09cb4b393d
error: cannot connect to 'root@r4.local'
exit status 1

This happens even when I explicitly specify the keyfile using SSH_IDENTITY_FILE and even SSH_SKIP_HOST_KEY_CHECK. Is there some kind of sandboxing that has been added since I upgraded last? Or is there a way for me to see exactly why the connection is failing?

Thanks for the support. If there is a Matrix room or anything like that where this is more appropriate to ask, please feel free to direct me there.

DBCDK / morph

Connection fails when deploying, but works outside of morph #207