PHP formatting with mago format works on CLI, but deletes the text in Helix

[leaf-node]

I can format the following file with mago format:

<?php

    echo "hello world\n";

$ mago format foo.php 
 INFO Formatted 1 file(s) successfully.

.config/helix/languages.toml:

[[language]]
name = "php"
formatter = { command = "mago", args = ["format"] }

However when I run :fmt in Helix, the text in the editor is deleted, so it becomes an empty page. If I type u to undo, the text comes back again.

$ hx --version 
helix 25.07.1 (a05c151b)

EDIT: I see no log messages in ~/.cache/helix/helix.log when opening, editing or formatting this file.

[waddie]

Include the flag --stdin-input:

[[language]]
name = "php"
formatter = { command = "mago", args = ["format", "--stdin-input"] }

[leaf-node]

Yes, that's it. Thank you! : )