pi-prewalk

A pi extension that lets a strong model do the planning, then hands the mechanical implementation off to a fast/cheap model.

Ported from oh-my-pi ("prewalk" behaviour).

How it works

Prewalk is a one-way switch, armed either at startup or mid-session. Once armed:

1. Plan nudge — a hidden deep-plan prompt is steered in so the strong model commits to a complete plan and seeds a todo list before touching code.
2. Continue safety net — one extra turn is re-armed after a text-only reply, so a plan-only turn never ends the run with no code written.
3. The switch — once the todo list exists AND the model makes its first edit/write (the "todo gate"), the session switches to the fast target model and a verification checklist is steered in. The plan nudge is scrubbed from the LLM context at the switch: the fast model inherits the plan, not the nudge.

bash is deliberately not a trigger tool (it doubles as exploration), and the todo call itself is deliberately not a trigger (firing there would hand the fast model the whole implementation cold).

Install

pi install npm:pi-prewalk

Or try it for a single run without installing:

pi -e npm:pi-prewalk

From git instead of npm:

pi install git:github.com/lukeramsden/pi-prewalk

Usage

pi --prewalk                     # arm at startup, default target (GLM-5.2 on opencode)
pi --prewalk-into anthropic/...  # arm at startup, explicit target

Or inside a session:

/prewalk                         # arm now, default target (GLM-5.2 on opencode)
/prewalk <provider/model|model>  # arm now, explicit target
/prewalk off                     # disarm
/prewalk status                  # show current state

If the default target (opencode/glm-5.2) has no configured API key, prewalk falls back to the cheapest available model with a warning.

Development

npm install
npm run verify

verify runs the typecheck (tsc --noEmit) plus headless functional checks (scripts/verify.mjs): the extension is loaded with jiti — the same loader pi uses — and driven through a mock ExtensionAPI to assert the full arm → todo-gate → model-switch → context-scrub flow, with no pi binary, models, or API keys needed. The same command runs in CI (.github/workflows/verify.yml) and gates every publish (.github/workflows/publish.yml).

The extension is plain TypeScript loaded by pi via jiti — no build step. Pi's core packages (@earendil-works/pi-ai, @earendil-works/pi-coding-agent) are peerDependencies; they are provided by pi at runtime and installed locally only for typechecking.

Releasing

Publishing is done from GitHub Actions via npm trusted publishing (OIDC) — no npm tokens stored anywhere. Pushing a version tag publishes to npm with a provenance attestation:

npm version patch        # or minor / major — bumps, commits, tags vX.Y.Z
git push --follow-tags   # the v* tag triggers .github/workflows/publish.yml

License

MIT