feat(herdr): add plugin for herdr (#14079)

plugins/herdr/README.md

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+# herdr plugin
+
+This plugin adds completion, aliases, an interactive session picker and a prompt
+function for [herdr](https://herdr.dev), the runtime your
+coding agents live on. herdr keeps agent terminals running in the background across
+projects and machines, so you can close your terminal, reconnect later, and pick up
+where the agents left off.
+
+To use it, add `herdr` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... herdr)
+```
+
+Install herdr first if you have not already:
+
+```sh
+curl -fsSL https://herdr.dev/install.sh | sh   # or: brew install herdr
+```
+
+## Learning herdr from the terminal
+
+The fastest way to explore herdr is tab completion. Every command group and flag shows a
+short description, so you can discover what is available without leaving the shell:
+
+```
+$ herdr <TAB>
+agent         -- Control and inspect agent panes
+session       -- Manage named persistent sessions
+workspace     -- Manage workspaces over the socket API
+worktree      -- Manage Git worktree-backed workspaces
+...
+$ herdr agent <TAB>
+list          -- List agents
+prompt        -- Submit a prompt to an agent
+start         -- Start a supported interactive agent in an existing pane
+wait          -- Wait until an agent reaches one of the requested states
+...
+```
+
+A few other ways to learn as you go:
+
+- `herdr <group>` with no subcommand prints that group's help, for example `herdr pane`.
+- `herdr --skill` prints the instructions herdr gives to agents that drive it. It is a
+  good tour of the full command surface.
+- Most control commands return JSON, so you can pipe them into `jq` in scripts.
+
+## Common workflows
+
+### Start and reconnect
+
+```sh
+herdr                          # launch, or attach to the default session
+herdr --session work           # use or create a named session
+herdr session list             # see running and stopped sessions
+herdr session attach work      # reconnect to a named session
+herdr status                   # check the local client and running server
+herdr update                   # install the latest release
+```
+
+### Organize work into workspaces and tabs
+
+```sh
+herdr workspace list
+herdr workspace create --cwd ~/projects/app
+herdr tab create
+herdr pane split --direction right
+herdr worktree create --branch feature/login   # open a Git worktree in its own workspace
+```
+
+### Run and watch agents
+
+```sh
+herdr agent list                               # what is running, and is it idle, working or blocked
+herdr agent start reviewer --kind claude --pane w1:p2
+herdr agent prompt reviewer "review the last commit" --wait
+herdr agent read reviewer                      # read the agent's terminal output
+herdr agent wait reviewer --until idle
+herdr agent attach reviewer                    # jump straight into that terminal
+```
+
+### Work across machines
+
+```sh
+herdr --remote user@build-box                  # attach through SSH with your local keybindings
+```
+
+### Keep the server healthy
+
+```sh
+herdr config check                             # validate config.toml
+herdr server reload-config                     # apply config changes without restarting panes
+herdr server stop
+herdr channel set preview                      # switch between stable and preview releases
+herdr integration status                       # which agent CLIs have herdr hooks installed
+```
+
+See the [CLI reference](https://herdr.dev/docs/cli-reference/) for every command and flag.
+
+## Aliases
+
+| Alias   | Command                       |
+| ------- | ----------------------------- |
+| `hrdr`   | `herdr`                       |
+| `hrdrst` | `herdr status`                |
+| `hrdrup` | `herdr update`                |
+| `hrdrsl` | `herdr session list`          |
+| `hrdrsa` | `herdr session attach`        |
+| `hrdrr`  | `herdr --remote`              |
+| `hrdral` | `herdr agent list`            |
+| `hrdrwl` | `herdr workspace list`        |
+| `hrdrwc` | `herdr workspace create`      |
+| `hrdrwt` | `herdr worktree create`       |
+| `hrdrps` | `herdr pane split`            |
+| `hrdrrc` | `herdr server reload-config`  |
+
+Tab completion works through the aliases too, so `hrdr agent <TAB>` completes the same
+way `herdr agent <TAB>` does.
+
+## Session picker
+
+`hrdrs` lists your herdr sessions and attaches to the one you pick. It uses
+[fzf](https://github.com/junegunn/fzf) when it is installed and falls back to a numbered
+menu otherwise, so it works everywhere.
+
+```
+$ hrdrs
+name                 status   directory
+1) default              running  /Users/me/.config/herdr
+2) work                 stopped  /Users/me/projects/app
+Attach to session: 2
+```
+
+## Prompt
+
+This plugin provides the `herdr_prompt_info` function to show the current pane ID in
+your prompt when the shell is running inside herdr. It reads environment variables only,
+so it adds no cost to prompt rendering.
+
+For example:
+```
+PROMPT="%~$ "
+RPROMPT='$(herdr_prompt_info)'
+```
+changes your prompt inside a herdr pane to:
+```
+~/projects/app$ ▋                                                    w1:p4
+```
+and shows nothing outside herdr.
+
+Wrap it with `ZSH_THEME_HERDR_PROMPT_PREFIX` and `ZSH_THEME_HERDR_PROMPT_SUFFIX`, for
+example:
+```
+ZSH_THEME_HERDR_PROMPT_PREFIX="%{$fg[cyan]%}[herdr "
+ZSH_THEME_HERDR_PROMPT_SUFFIX="]%{$reset_color%}"
+```
+
+## Cache
+
+This plugin caches the completion script and automatically updates it when the plugin is
+loaded, which is usually when you start a new terminal emulator.
+
+The cache is stored at `$ZSH_CACHE_DIR/completions/_herdr`.

plugins/herdr/herdr.plugin.zsh

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+# Aliases, helpers and completion for herdr (https://herdr.dev), the runtime for coding agents.
+
+# PROMPT
+# Defined before the herdr check so themes can reference it on machines without herdr.
+function herdr_prompt_info {
+  [[ "$HERDR_ENV" == 1 ]] || return
+  echo "${ZSH_THEME_HERDR_PROMPT_PREFIX}${HERDR_PANE_ID:gs/%/%%}${ZSH_THEME_HERDR_PROMPT_SUFFIX}"
+}
+
+if (( ! $+commands[herdr] )); then
+  return
+fi
+
+# ALIASES
+alias hrdr='herdr'
+alias hrdrst='herdr status'
+alias hrdrup='herdr update'
+alias hrdrsl='herdr session list'
+alias hrdrsa='herdr session attach'
+alias hrdrr='herdr --remote'
+alias hrdral='herdr agent list'
+alias hrdrwl='herdr workspace list'
+alias hrdrwc='herdr workspace create'
+alias hrdrwt='herdr worktree create'
+alias hrdrps='herdr pane split'
+alias hrdrrc='herdr server reload-config'
+
+# FUNCTIONS
+# Pick a session and attach to it, with fzf if available or a numbered menu otherwise.
+function hrdrs {
+  setopt localoptions extendedglob
+  local -a lines
+  lines=("${(@f)$(herdr session list 2>/dev/null)}")
+  lines=("${(@)lines%%[[:space:]]#[^[:space:]]#}")  # drop the socket column
+  if (( $#lines < 2 )); then
+    print "hrdrs: no herdr sessions found" >&2
+    return 1
+  fi
+
+  local choice
+  if (( $+commands[fzf] )); then
+    choice=$(print -l -- "${lines[@]}" | fzf --header-lines=1 --prompt='herdr session> ') || return
+  else
+    print -- "${lines[1]}"
+    local PS3="Attach to session: "
+    select choice in "${lines[@]:1}"; do
+      [[ -n "$choice" ]] && break
+    done
+  fi
+  [[ -n "$choice" ]] || return 1
+
+  herdr session attach "${${(z)choice}[1]}"
+}
+
+# COMPLETION
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `herdr`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_herdr" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _herdr
+  _comps[herdr]=_herdr
+fi
+
+zmodload -F zsh/files b:zf_mv
+() {
+  local TMPPREFIX="$ZSH_CACHE_DIR/completions/_herdr"
+  zf_mv -f -- =( herdr completion zsh < /dev/null 2> /dev/null ) "$TMPPREFIX"
+} &|