prewalk for Codex and Claude Code

Prewalk lets a strong planner do the expensive repository work, then gives a configured executor a verified starting point and a self-contained handoff:

planner:  explore -> capped plan -> task 1 + verification -> root Stop checkpoint
                                                                          |
                                              review or automatic fast mode
                                                            |
executor: structured packet -> remaining tasks -> verify -> COMPLETE / INCOMPLETE

Use it for changes where understanding the repository is a meaningful part of the work. Skip it for a one-file fix or one or two small edits.

Start in three steps

Prewalk 0.4.0 requires Python 3.10+, Codex CLI 0.146.0+, or Claude Code 2.1.145+. Upgrade the host CLI before installing when it is older.

Codex

codex plugin marketplace add TerenceLiu98/prewalk
codex plugin add prewalk@prewalk-marketplace

Restart Codex, then run in the session you want to use as the planner:

$prewalk:prewalk Add a settings page with tests
$prewalk:pw-go

Before spawning, pw-go inspects the available spawn_agent capability. When the runtime cannot route an explicit executor model and the preset requires it, Prewalk directs you to /model <executor> followed by $prewalk:pw-resume.

Claude Code

claude plugin marketplace add TerenceLiu98/prewalk
claude plugin install prewalk@prewalk

Restart Claude Code, then run:

/prewalk:prewalk Add a settings page with tests
/prewalk:pw-go

Claude rewrites only the token-bearing Agent call, binds its lifecycle identity, and accepts a completion marker only from that executor's SubagentStop event.

Upgrade

# Codex
codex plugin marketplace upgrade prewalk-marketplace
codex plugin add prewalk@prewalk-marketplace

# Claude Code
claude plugin marketplace update prewalk
claude plugin update prewalk@prewalk

Restart the host after upgrading so the new hooks and skills are loaded. Users upgrading from 0.3.1 should read the 0.4.0 migration guide before their first run; v3 state is intentionally reset and legacy planner fields no longer configure the active session.

Commands

Action	Codex	Claude Code
Start	$prewalk:prewalk <task>	/prewalk:prewalk <task>
Review and hand off	$prewalk:pw-go	/prewalk:pw-go
Revise the plan	$prewalk:pw-revise <changes>	/prewalk:pw-revise <changes>
Show state	$prewalk:pw-status	/prewalk:pw-status
Disarm	$prewalk:pw-off	/prewalk:pw-off
Diagnose setup	$prewalk:pw-doctor	/prewalk:pw-doctor
Retry an incomplete route	$prewalk:pw-retry	/prewalk:pw-retry
Reconcile an ambiguous route	$prewalk:pw-reconcile	/prewalk:pw-reconcile
Manual-model compatibility	$prewalk:pw-resume	/prewalk:pw-resume

Clients may display shorter aliases or a leading slash, such as /$prewalk:prewalk. These refer to the same namespaced skills.

Add --preset <name> before task text to select a model pair. Add --fast (legacy alias: --no-pause) to skip human review after the checkpoint:

$prewalk:prewalk --preset backend --fast Optimize the job queue
/prewalk:prewalk --preset frontend Rebuild the dashboard and verify screenshots

Fast mode still validates the checkpoint and confirms routing. It only removes the wait for pw-go.

What the planner must produce

The planner explores the relevant entry points, configuration, tests, and local patterns. It creates at most the preset's max_todos; every real item includes a test/build/verify/check criterion. It then completes and verifies only task 1.

The handoff is accepted only when the snapshot contains:

• a non-empty, capped todo list;
• task 1 marked completed;
• at least two remaining real tasks worth delegating;
• the required packet headings and verification evidence, or an explicit verification warning.

The planner stops with a structured Handoff Packet:

Goal
Files Read
Constraints And Existing Patterns
Full Todo List
Task 1 Changes
Verification Already Run
Remaining Work
Risks / Do Not Repeat

This packet, not the planner's raw context, becomes the executor's fresh context. The executor must finish with PREWALK_COMPLETE or PREWALK_INCOMPLETE: <reason>.

Configuration

Preset files are optional for a first run; each host has built-in fallbacks. Create one when the default model names do not exist in your environment or you want multiple routes.

Host	Optional preset file	Format
Codex	~/.codex/prewalk-presets.toml	TOML
Claude Code	~/.claude/prewalk-presets.json	JSON

CODEX_HOME and CLAUDE_CONFIG_DIR relocate both preset and state files. Templates are in codex/presets.example.toml and claude-code/presets.example.json.

A preset configures the executor; the active root session remains the planner:

Field	Meaning
executor	Host-resolvable executor model
max_todos	Maximum real tasks in the handoff plan
executor_effort	Requested effort when the host exposes a per-spawn control
handoff_mode	auto, spawn, or manual-model
require_model_routing	Refuse an unpinned executor spawn when true

Example TOML:

default_preset = "code-value"

[presets.code-value]
executor = "gpt-5.6-terra"
max_todos = 12
executor_effort = "medium"
handoff_mode = "auto"
require_model_routing = true

Legacy planner and planner_thinking fields are ignored with a deprecation warning. executor_thinking is accepted as a deprecated alias for executor_effort. Codex requests effort only when the live spawn_agent schema supports it; Claude currently reports dynamic executor effort as unsupported.

Handoff and recovery

	Codex	Claude Code
Route	Native spawn_agent, explicit model and fresh context when supported	Token-bearing Agent input rewritten to executor model/subagent
Confirmation	Spawn PostToolUse binds the returned agent; bound SubagentStop owns the result	PostToolUse acknowledges launch; bound SubagentStop owns the result
Failure	Durable incomplete; recover with pw-retry	Durable incomplete; recover with pw-retry
Incomplete executor	pw-retry or pw-reconcile; pw-resume is explicit manual fallback	pw-retry, or pw-reconcile after proving the agent stopped

pw-status shows phase, host, executor route, evidence, a non-secret token fingerprint, bound agent, timestamps, remaining work, last error, and one safe next command. An overdue route becomes stale but is never cleared or stopped. pw-reconcile requires explicit proof that its agent is no longer running. pw-off clears only Prewalk state; it does not stop an agent or edit files/todos.

State is stored per session in prewalk-state.json. Writes use a cross-process lock and atomic replacement. Malformed state is preserved as prewalk-state.json.corrupt before recovery.

Measure it locally

Prewalk does not send telemetry and does not claim a universal cost reduction. Record comparable baseline and Prewalk runs locally:

python3 scripts/benchmark.py record runs.jsonl --mode baseline --task "settings page" \
  --input-tokens 12000 --output-tokens 3000 --duration-seconds 420 --passed
python3 scripts/benchmark.py record runs.jsonl --mode prewalk --task "settings page" \
  --input-tokens 8000 --output-tokens 2800 --duration-seconds 360 --passed
python3 scripts/benchmark.py report runs.jsonl

The report compares run count, pass rate, average total tokens, and duration.

Development

The implementation uses Python 3.10+ and the standard library only. The canonical state machine is _shared/prewalk_core.py; both plugins vendor an identical copy.

./scripts/check.sh

The check runs unit and end-to-end tests, validates manifests and shell entry points, compares shared-core copies, and smoke-installs both integrations. CI runs it on Linux and macOS across supported Python versions.

Detailed host notes: Codex and Claude Code. Release history is in CHANGELOG.md, and upgrade details are in MIGRATION.md. The accepted 0.4.0 lifecycle contract is ADR 0001.

Attribution

The technique comes from Can Boluk / Stencil's "You only need the frontier model for one single edit". Reference implementations and mechanisms include westfable/hermes-prewalk, Daniel-97/opencode-prewalk, and tzachbon/claude-model-router-hook. This repository's shared engine and adapters are MIT-licensed.