Add Fish custom prompts

[hdp617]

Summary

Fish used default prompts while zsh/tmux show USER at <~/.name>. This adds custom Fish prompts aligned with that layout and wires in the existing fish_git_prompt configuration from 55-git-prompt.fish.

Changes

• fish_prompt.fish — truncated cwd (prompt_pwd), ! on failure, > arrow (red for root).
• fish_right_prompt.fish — user at machine + fish_git_prompt.
• _machine_name.fish — reads ~/.name, falls back to hostname -s.
• README: fix PATH filename and document the new prompt functions.

Test plan

• chezmoi apply and open a new Fish session
• Confirm left prompt shows cwd and >
• Confirm right prompt shows user at <name> and git branch/state in a repo

  

[gemini-code-assist]

Code Review

This pull request updates the README layout notes and introduces custom Fish shell prompt configurations, including a left prompt, a right prompt, and a helper function to resolve the machine name. The review feedback focuses on optimizing shell performance by avoiding spawning external processes (such as cat, hostname, id, and whoami) on every prompt render. It suggests using built-in Fish features like read, prompt_hostname, fish_is_root_user, and the $USER environment variable, as well as caching the resolved machine name.

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[gemini-code-assist]

Spawning external processes like cat and hostname on every prompt render introduces unnecessary latency and slows down terminal responsiveness. We can optimize this by using the built-in read command to read the file without forking, using the built-in prompt_hostname function, and caching the resolved machine name in a global variable so it is only computed once per session.

    if not set -q __machine_name_cache
        if test -f $HOME/.name
            read -l name < $HOME/.name
            set -g __machine_name_cache (string trim $name)
        else
            set -g __machine_name_cache (prompt_hostname)
        end
    end
    echo -n $__machine_name_cache

[gemini-code-assist]

Using (id -u) spawns an external process on every single prompt render, which can degrade shell performance. Fish provides a built-in function fish_is_root_user that checks user privileges extremely quickly without spawning any external processes.

    if fish_is_root_user
        echo -n (set_color red)'>'(set_color normal)' '
    else
        echo -n (set_color magenta)'>'(set_color normal)' '
    end

[gemini-code-assist]

Spawning external processes like (id -u) and (whoami) on every right prompt render degrades terminal responsiveness. We can optimize this by using the built-in fish_is_root_user function and the standard $USER environment variable, avoiding external process forks entirely.

    if fish_is_root_user
        echo -n (set_color red)"$USER"(set_color normal)
    else
        echo -n (set_color magenta)"$USER"(set_color normal)
    end