pi-herdr

A Pi extension for the Herdr CLI — control workspaces, tabs, panes, and coding agents through a typed tool that calls the local herdr CLI directly.

Why

Pi can already shell out to the herdr CLI via bash, but a bare skill describing CLI flags is easy to misuse: the model runs bare herdr (launching the TUI), forgets to check HERDR_ENV, or runs herdr server stop by accident. This extension packages the CLI behind a typed tool with:

• a subcommand + args map that serializes to the CLI's --flag value format (booleans → bare flags, no shell quoting needed)
• HERDR_ENV=1 precondition — the tool refuses to run outside a Herdr-managed pane and returns actionable guidance instead of failing opaquely
• bare-herdr rejection — empty subcommand throws with a warning that bare herdr launches the TUI
• prompt guidance injected when a prompt mentions herdr / pane / workspace / tab / agents
• a live skill generated from herdr --skill at session start (always matches the installed herdr version; falls back to a bundled static copy outside Herdr)
• safety guards — refuses server stop unless forceDangerous: true
• output truncation consistent with Pi's built-in tools

Requirements

• The herdr CLI on your PATH
• Running inside a Herdr-managed pane (HERDR_ENV=1) — the tool is a no-op otherwise and returns guidance

Install

As a Pi package

pi install npm:@sfroment/pi-herdr

Or pin a version:

pi install npm:@sfroment/pi-herdr@0.1.0

Then /reload in Pi.

From git

pi install git:github.com:sfroment/pi-herdr@v0.1.0

Manually

Copy or symlink this directory into ~/.pi/agent/extensions/herdr/, then /reload.

Tool reference

The herdr tool takes:

param	type	description
subcommand	string (required)	CLI subcommand, e.g. agent list, pane split, workspace create. Split on spaces into the command path.
args	object	Key/value flags. Booleans become bare flags ({"no-focus": true} → --no-focus). Strings/numbers become --flag value pairs. Arrays become repeated --flag value pairs.
timeoutSeconds	int	Default 30, max 120.
forceDangerous	bool	Opt-in for destructive commands (server stop). Requires explicit user confirmation.

Examples

// list agents
{ "subcommand": "agent list" }

// split a pane to the right, keep focus on caller
{ "subcommand": "pane split", "args": { "--current": true, direction: "right", "no-focus": true } }

// start a codex agent named "reviewer" in a pane
{ "subcommand": "agent start reviewer", "args": { kind: "codex", pane: "w1:p2" } }

// read recent output from a pane
{ "subcommand": "pane read w1:p1", "args": { source: "recent-unwrapped", lines: 120 } }

Develop

git clone git@github.com:sfroment/pi-herdr.git
cd pi-herdr
bun install
bun test

The tests mock only the system boundary (pi.exec) via dependency injection — runHerdr(params, exec) takes the exec function as a parameter, so tests pass a fake that records argv and returns canned results. Internal helpers (buildArgv, assertSafeCommand, formatOutput) are pure and tested directly.

The pretest script (scripts/link-pi-deps.sh) symlinks the pi runtime packages (@earendil-works/pi-coding-agent, @earendil-works/pi-ai, typebox) into node_modules/ so Bun can resolve the extension's imports during tests.

License

Licensed under the GNU General Public License v3.0.