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