---
name: how
description: "Use for \"how does X work\", code walkthroughs before changing something, and placement / ownership / layering questions (\"where should this live\", \"which package owns this\", \"is this the right layer\"). Explains subsystem architecture, runtime flow, onboarding mental models. Use why for motivation."
disable-model-invocation: true
---

# How

In Codex, read [the Codex adapter](../../docs/harness/codex.md) once per session before you follow this skill. It maps the Claude Code names in pstack skills to Codex.

Another pstack skill named here, as the **name** skill or `/name`, lives at `../<name>/SKILL.md`. Read that file and follow it, because the `Skill` tool refuses most pstack skills. When you tell the user to type one, write `/pstack:<name>`.

Explore the codebase to answer "how does X work?" questions. Produce architectural explanations at the level of a senior engineer onboarding onto a subsystem, enough to build a working mental model, not so much that it reads like annotated source code.

Every spawn is an `Agent` subagent with `subagent_type: "Explore"`. Each brief says "do not edit files", and you check `git status` after the spawns return. Explorers use the `how explorer` line in the `pstack-models.md` rule (default `haiku medium`), and every explainer uses the `how explainer` line (default `opus xhigh`). A value is `<model> <effort>`, passed as the `Agent` call's `model` and `effort`. Use that line's value, or the default if the rule or the line is missing. Leave both unset when the value is `inherit`. If the `Agent` tool rejects a value, use the default and say so. If it rejects the default too, follow the fallback in the Subagents section of the **poteto-mode** skill. Pick each subagent's effort for the job, per the Subagents section of the **poteto-mode** skill.

## 1. Assess complexity

If the scope is ambiguous, state your interpretation and explore. The user can redirect.

- **Simple** (a single module, a small utility, a narrow question such as "how does function X work"): no explorers. Spawn one explainer that explores and explains in one pass, built from `references/explainer-prompt.md` without the explorer-findings section. Go to step 4.
- **Complex** (a subsystem spanning multiple files or services, a cross-cutting feature, a full architectural overview): go to step 2.

When in doubt, take the simple path.

## 2. Explore (complex only)

Decompose the question into 2 to 4 angles, each a distinct slice of the subsystem. Spawn all explorers in a single message, each with `references/explorer-prompt.md` and its angle filled in.

## 3. Synthesize (complex only)

Once all explorers have returned, spawn one explainer with `references/explainer-prompt.md` and every explorer's findings filled in.

## 4. Present

Present the explainer's output. Light edits for clarity or context from the conversation are fine. Do not substantially rewrite it.

## Output format

The explanation uses the sections defined in `references/explainer-prompt.md`, dropping any that do not apply: Overview, Key Concepts, How It Works, Where Things Live, Gotchas.