improve-codebase-architecture

# Improve Codebase Architecture Surface architectural friction and propose **deepening opportunities** — refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability. Built on a shared design vocabulary: run the `codebase-design` skill for the architecture vocabulary (**module**, **interface**, **depth**, **seam**, **adapter**, **leverage**, **locality**) and its principles (the deletion test, "the interface is the test surface", "one adapter = hypothetical seam, two = real"). Use these terms exactly in every suggestion — don't drift into "component," "service," "API," or "boundary." Where the project keeps a domain glossary (an `AGENTS.md` glossary section or `CONCEPTS.md`), its terms give names to good seams. ## Process ### 1. Explore **Scope before you scan — YAGNI.** Deepening a module pays off by making future changes to it easier, so put extra weight on the parts of the codebase that have recently changed. Decide _where_ to look before you look: - If the user named a direction — a module, a subsystem, a pain point — take it, and skip the inference below. - Otherwise, walk back a good stretch of the commit history (`git log --oneline`) to find the codebase's hot spots — the files and areas that keep coming up — and let those paths pull your attention first. If the changes are scattered with no clear hot spot, widen the net. Read the project's domain glossary first, and search `docs/solutions/` for learnings and recorded rejectio...