Toolchain

Opinionated toolchain enforcement for pi. Transparently mutates commands to use preferred tools or blocks mismatched commands.

Installation

pi install npm:@aliou/pi-toolchain

Or from git:

pi install git:github.com/aliou/pi-toolchain

Features

Each feature is independently set to one of three modes:

• "disabled": no action taken
• "mutate": transparently mutate matching commands before shell execution
• "block": block matching commands via tool_call hook

nodePackageManager

Mutates or blocks npm/yarn/bun commands to use the selected package manager. Also handles npx -> pnpm dlx/bunx.

pythonToPython3

Mutates or blocks bare python commands to use python3.

pythonToUv

Mutates or blocks python/python3 to uv run python and pip/pip3 to uv pip.

nonInteractiveGitRebase

Injects GIT_EDITOR=true and GIT_SEQUENCE_EDITOR=: env vars for git rebase commands so they run non-interactively. Only supports "disabled" and "mutate" modes (block is not applicable).

Settings Command

Run /toolchain:settings to open an interactive settings UI with two tabs:

• Local: edit project-scoped config (.pi/extensions/toolchain.json)
• Global: edit global config (~/.pi/agent/extensions/toolchain.json)

Use Tab / Shift+Tab to switch tabs. Feature modes and the package manager can be changed directly. Configure mutation notification visibility in JSON for now.

Configuration

Configuration is loaded from two optional JSON files, merged in order (project overrides global):

• Global: ~/.pi/agent/extensions/toolchain.json
• Project: .pi/extensions/toolchain.json

Configuration Schema

{
  "enabled": true,
  "features": {
    "nodePackageManager": "disabled",
    "pythonToPython3": "disabled",
    "pythonToUv": "disabled",
    "nonInteractiveGitRebase": "mutate"
  },
  "nodePackageManager": {
    "selected": "pnpm"
  },
  "ui": {
    "showMutationNotifications": false
  }
}

All fields are optional. Missing fields use the defaults shown above.

Feature Defaults

Feature	Default	Description
nodePackageManager	"disabled"	Opt-in. Mutates or blocks package-manager commands.
pythonToPython3	"disabled"	Opt-in. Mutates or blocks bare python commands to python3.
pythonToUv	"disabled"	Opt-in. Mutates or blocks python/pip commands to uv equivalents.
nonInteractiveGitRebase	"mutate"	On by default. Injects non-interactive env vars for git rebase.
ui.showMutationNotifications	false	Show a Pi notification each time a mutation happens.

Examples

Enforce pnpm, mutate python commands, and show mutation notifications:

{
  "features": {
    "nodePackageManager": "mutate",
    "pythonToUv": "mutate"
  },
  "nodePackageManager": {
    "selected": "pnpm"
  },
  "ui": {
    "showMutationNotifications": true
  }
}

Block package-manager mismatches instead of mutating them:

{
  "features": {
    "nodePackageManager": "block"
  },
  "nodePackageManager": {
    "selected": "pnpm"
  }
}

How It Works

Mutations vs Blockers

The extension uses pi's tool_call event hook:

1. Blockers: Commands that match a feature set to "block" are rejected with a reason. The agent sees the block reason and retries with the correct command.
2. Mutations: Commands that match a feature set to "mutate" are transparently rewritten before shell execution. The agent sees the original command in the tool call UI but gets the output of the mutated command.
3. Mutation notifications: When ui.showMutationNotifications is enabled, a warning-level Pi notification is shown for each mutation.

AST-Based Rewriting

All rewriters use structural shell parsing via @aliou/sh to identify command names in the AST. This avoids false positives where tool names appear in URLs, file paths, or strings. If the parser fails, the command passes through unchanged -- a missed mutation is safe, a false positive mutation corrupts the command.

Migration from Guardrails

If you were using preventBrew, preventPython, or enforcePackageManager in your guardrails config:

1. Install @aliou/pi-toolchain
2. Create .pi/extensions/toolchain.json with the equivalent config
3. Remove the deprecated features from your guardrails config

The guardrails extension will continue to honor these features with a deprecation warning until they are removed in a future version.