Subsystem walkthrough

Leading words: mental model, one explainer, parallel slices, inherit host model.

Answer "how does X work?" at the level of a senior engineer onboarding onto the subsystem. Not annotated source.

Copy these steps into the todo list verbatim. Skip with skip: <reason>.

1. Assess complexity. Simple → one explainer. Complex → 2–4 read-only explorers, then one synthesizer. Write Complexity: simple or Complexity: complex (N slices) as the first line of the output.
2. Explore or explain (see below). Inherit the host model. Do not hardcode a slug.
3. Present the explainer output with light edits only. Keep the Complexity line.

When in doubt, take the simple path.

Simple

One read-only subagent explores and explains in a single pass. Fill references/explainer-prompt.md without explorer findings.

Complex

Decompose into 2–4 distinct slices. Spawn explorers in one message, each with references/explorer-prompt.md. Then one synthesizer with the explainer template and every explorer's findings filled in. If the host cannot spawn subagents, run the slices sequentially yourself.

Output

First line: Complexity: simple or Complexity: complex (N slices).

Then: Overview / Key Concepts / How It Works / Where Things Live / Placement / Gotchas. Drop a section that does not apply. Placement is where new code for this subsystem should live (package, file, layer) — one short paragraph, not a second architecture essay.

Reply contract

The Complexity line, then the explanation. Do not rewrite it into a different structure after the explainer returns.