pi-herdr-worktree

An extension for the Pi and Oh My Pi terminal coding agents. It gives the model one herdr_worktree tool that runs a fixed set of Herdr Git worktree operations, instead of letting it type herdr commands into a shell.

If any of those names are new to you:

• Herdr is a terminal workspace manager for coding agents. It can back a workspace with a Git worktree, so a branch gets its own checkout, its own tabs, and its own panes.
• Pi and Oh My Pi are terminal coding agents. An extension is an npm package they load at startup to add tools the model can call.

Why

An agent with shell access can already run herdr, but a shell gives it a free-form command string. Herdr's CLI does not accept --flag=value, so every value is a separate argument, and a value that starts with - silently becomes a flag. A wrong --workspace deletes the wrong checkout, --force throws away uncommitted work, and --focus moves the user's view away from what they were doing.

This extension replaces that with a closed set of operations. Each one accepts only its own typed fields, builds a fixed argument array, checks the repository before running, and verifies the result against Git afterwards. There is no shell string anywhere.

Requirements

• Node.js 22 or newer
• Git 2.36 or newer
• Herdr 0.8.2 or newer, and an agent running inside a Herdr-managed pane

The extension loads anywhere. Outside a Herdr pane, outside a Git work tree, or without the herdr CLI, a tool call fails with an explanatory error rather than running an unsupported command.

Install

Pi:

pi install npm:@mcuste/pi-herdr-worktree

Oh My Pi:

omp plugin install @mcuste/pi-herdr-worktree

Or through the Oh My Pi marketplace:

/marketplace add mcuste/pi-herdr-worktree
/marketplace install pi-herdr-worktree@pi-herdr-worktree

From a local checkout:

pnpm install
pi install /absolute/path/to/pi-herdr-worktree
omp plugin link /absolute/path/to/pi-herdr-worktree

What the tool does

One tool named herdr_worktree, selected by an operation field:

| Operation | Runs | Purpose | | --- | --- | --- | | list | herdr worktree list | Read every worktree of the current repository | | create | herdr worktree create | Add a worktree on a new branch and open it as a workspace | | open | herdr worktree open | Open an existing worktree as a workspace | | remove | herdr worktree remove | Delete a worktree checkout and close its workspace |

list is read-only. The other three change the repository and the session, and Oh My Pi asks for execute approval; remove always prompts, and so does a create that names its own path. Full per-operation fields and guarantees are in docs/operations.md.

System prompt note

The tool loads on demand, so its description is not in the base prompt. The model can reach for herdr or git worktree in a shell before it sees the tool, so the extension appends one note to the system prompt at the start of each turn:

Use the herdr_worktree tool for Git worktrees, not herdr or git worktree in bash. Create a worktree when work needs its own checkout, for example parallel multi-agent work.

The note is added once per prompt, only where detection succeeds, and only in a host that offers the before_agent_start event. A host without that event still gets the tool.

Detection reads HERDR_ENV first. That variable belongs to the process, so outside Herdr the extension starts no child process at all. Inside a Herdr pane, detection also finds the Git repository and reads the herdr version, then caches the result in memory for ten minutes. A failed detection is cached for five minutes, so a directory that is not a Git work tree does not run git and herdr on every turn.

What is deliberately missing

• Workspace, tab, pane, and agent control (herdr workspace, herdr tab, herdr pane, herdr agent) is a separate concern. This extension only manages worktree-backed workspaces.
• Session and server control (herdr session, herdr server, herdr update) can stop the user's session and every process in it.
• herdr worktree remove without a verified target. The tool always lists the repository's worktrees first and refuses a workspace that does not hold a linked worktree of it.

For anything else, the model works through the normal Herdr workflow with the user in the loop.

Safety

Every operation checks the repository before and after it runs: a new worktree must be registered by Git on the requested branch, an opened worktree must be the one that was asked for, and a removed checkout must be gone from git worktree list. A failed check is reported as an uncertain result rather than retried.

Arguments are never concatenated into a shell command. Herdr does not accept --flag=value, so every value travels as its own argument and is rejected before spawning if it starts with -. Each value also carries the option it was parsed for, so a label cannot arrive as a branch. See docs/safety.md.

Focus defaults to off. The tool passes --no-focus unless the caller explicitly asks to move the user's view.

Documentation

• Operations reference
• Safety model
• Development and release
• Changelog

License

MIT