In a minimal chroot without procps installed:

# apt install fish
# fish
# kill
fish: Unknown command: kill
/usr/share/fish/config.fish (line 232):
    command kill (__fish_expand_pid_args $argv)
            ^~~^
in function 'kill'
fish: Unknown command: kill
/usr/share/fish/config.fish (line 232):
    command kill (__fish_expand_pid_args $argv)
            ^~~^
in function 'kill' with arguments '-t'
        called on line 31 of file /usr/share/fish/functions/__fish_make_completion_signals.fish
in function '__fish_make_completion_signals'
        called on line 2 of file /usr/share/fish/functions/fish_status_to_signal.fish
in function 'fish_status_to_signal' with arguments '127'
        called on line 1 of file /usr/share/fish/functions/__fish_print_pipestatus.fish
in command substitution
        called on line 26 of file /usr/share/fish/functions/__fish_print_pipestatus.fish
in function '__fish_print_pipestatus' with arguments '\[ \] \| \e\[31m \e\[1m\e\[31m 127'
        called on line 1 of file /usr/share/fish/functions/fish_prompt.fish
in command substitution
        called on line 31 of file /usr/share/fish/functions/fish_prompt.fish
in function 'fish_prompt'
in command substitution
fish: Unknown command: kill
/usr/share/fish/config.fish (line 232):
    command kill (__fish_expand_pid_args $argv)
            ^~~^

# apt install procps

solves this.

Not sure if it should be Depends or Recommends but I triggered this with
other input as well, for example `cd ...`.

Cheers Jochen

We believe that the bug you reported is fixed in the latest version of
fish, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1029940@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Mo Zhou <lumin@debian.org> (supplier of updated fish package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Sat, 25 Mar 2023 10:20:50 -0400
Source: fish
Architecture: source
Version: 3.6.0-3
Distribution: unstable
Urgency: medium
Maintainer: Tristan Seligmann <mithrandi@debian.org>
Changed-By: Mo Zhou <lumin@debian.org>
Closes: 1029940
Changes:
 fish (3.6.0-3) unstable; urgency=medium
 .
   * Cherry-pick upstream fixes from the v3.6.1 branch.
   * Add the missing Depends on procps (Closes: #1029940).
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