How

Before following this workflow, read the Codex runtime contract. It defines plugin paths, model configuration, delegation, and persistence.

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.

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:

• use the default agent only if the current spawn schema exposes an agent selector
• model: your configured how-explorer model (default gpt-5.6-luna)
• read-only by instruction: forbid writes and mutating commands in the prompt

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 Codex subagent that explores and explains in one pass:

• use the default agent only if the current spawn schema exposes an agent selector
• model: your configured how-explainer model (default gpt-6-astra)
• read-only by instruction: forbid writes and mutating commands in the prompt

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 Codex subagent to synthesize their findings into one explanation:

• use the default agent only if the current spawn schema exposes an agent selector
• model: your configured how-explainer model (default gpt-6-astra)
• read-only by instruction: forbid writes and mutating commands in the prompt

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.