how

# How 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. Each spawn below names a role line in the `pstack-models.mdc` rule and a default. Set `model` to that line's value, or to the default if the rule or the line is missing. Leave `model` unset when the value is `auto` or `inherit-parent`. If the Task tool rejects a slug, use the default and say so. If it rejects the default, use the closest valid slug of the same family from its error message. ## Step 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. One explainer explores and explains in a single pass. Go to Step 2b. - **Complex** (a subsystem spanning multiple files or services, a cross-cutting feature, a full architectural overview): spawn parallel explorers first, then hand off to the explainer. Go to Step 2a. When in doubt, take the simple path. ## Step 2a. Explore (complex questions only) Decompose the question into 2 to 4 exploration angles, each a distinct slice of the subsystem. Spawn all explorers in a single message: - `subagent_type`: `generalPurpose` - `model`: the `how explorer` line, default `grok-4.7-xhigh-fast` - `readonly`: `true` Each explorer gets the prompt in `references/explorer-prompt.md` with its angle filled in. Then go to Step 3. ## Step 2b. Direct Explain (simple questions) Spawn one Task subagent that explores and explains in one pass: - `subagent_type`: `generalPurpose` - `model`: the `how explainer` line, default `claude-opus-5-5-max` - `readonly`: `true` Build its prompt from `references/explainer-prompt.md` without the explorer-findings section. Go to Step 4. ## Step 3. Synthesize (complex questions only) Once all explorers have returned, spawn one Task subagent to synthesize their findings into one explanation: - `subagent_type`: `generalPurpose` - `model`: the `how explainer` line, default `claude-opus-5-5-max` - `readonly`: `true` Build its prompt from `references/explainer-prompt.md` with every explorer's findings filled in. ## Step 4. Present Present the explainer's output to the user. 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.