Too bad, probably. I don't know any way to tell ssh always to fail non-interactively here.

If it shows up in verbose mode, that'll probably have to be good enough

You provided no way to reproduce this.

After writing the below I noticed -o BatchMode=yes which should disable any interactive prompts.

https://man.archlinux.org/man/ssh_config.5.en#BatchMode

I think -o StrictHostKeyChecking=yes would make this specific case fail non-interactively.

-o PasswordAuthentication=no I think would cover #9626

https://man.archlinux.org/man/ssh_config.5.en#StrictHostKeyChecking
https://man.archlinux.org/man/ssh_config.5.en#PasswordAuthentication

to reproduce the issue comment out any entries for github.com in ~/.ssh/known_hosts and ensure no system level ssh configuration disables host key checking for that host then use the following pyproject.toml

[tool.poetry]
name = "test"
version = "0.1.0"
description = ""
authors = [""]

[tool.poetry.dependencies]
poetry = { "git" = "[email protected]:python-poetry/poetry.git" }

poetry uses dulwich for git clones, so next step is to persuade dulwich to use that parameter then

suggest you experiment with something like

diff --git a/src/poetry/vcs/git/backend.py b/src/poetry/vcs/git/backend.py
index 0fc00f0b..b3b28026 100644
--- a/src/poetry/vcs/git/backend.py
+++ b/src/poetry/vcs/git/backend.py
@@ -194,7 +194,7 @@ class Git:
         client: GitClient
         path: str

-        kwargs: dict[str, str] = {}
+        kwargs = {"ssh_command": "ssh -o BatchMode=yes"}
         credentials = get_default_authenticator().get_credentials_for_git_url(url=url)

         if credentials.password and credentials.username:

and submit a merge request if you can get it to work satisfactorily

That isn't the only "failure case" for this though, the bug is that the "Resolving dependencies" message erases messages from the SSH client. E.g. if you are prompted to type in your passphrase to unlock your ssh key, that message gets erased and unless you notice the message flash for an instant and realize what it is, you'll spend hours trying to figure out why adding a git+ssh dependency suddenly starts making dependency resolution take forever. In other words, the messaging that it's resolving dependencies isn't actually accurate and overwriting the prompt that would allow it to proceed obscures what the user needs to do.

(In other words, dulwich seems to be doing the right thing, if only Poetry didn't overwrite the prompts.)