deepen

Files (5)

• DEEPENING.md
• HTML-REPORT.md
• INTERFACE-DESIGN.md
• LANGUAGE.md
• SKILL.md

SKILL.md (first lines)

# Improve Codebase Architecture

Surface architectural friction and propose **deepening opportunities** — refactors that turn shallow modules into deep ones. The aim: testability and AI-navigability.

## Vocabulary

Use these terms exactly in every suggestion. Consistent language is the point — don't drift into "component," "service," "API," or "boundary." Definitions in [LANGUAGE.md](LANGUAGE.md).

- **Module** — anything with an interface and an implementation (function, class, package, slice).
- **Interface** — everything a caller must know to use the module: types, invariants, error modes, ordering, config. Not just the type signature.
- **Implementation** — the code inside.
- **Depth** — leverage at the interface: a lot of behaviour behind a small interface. **Deep** = high leverage. **Shallow** = interface nearly as complex as the implementation.
- **Seam** — where an interface lives; a place behaviour can be altered without editing in place. (Use this, not "boundary.")
- **Adapter** — a concrete thing satisfying an interface at a seam.
- **Leverage** — what callers get from depth.
- **Locality** — what maintainers get from depth: change, bugs, knowledge concentrated in one place.

Key principles (see [LANGUAGE.md](LANGUAGE.md) for the full list):

- **Deletion test**: imagine deleting the module. If complexity vanishes, it was a pass-through. If complexity reappears across N callers, it was earning its keep.
- **The interface is the test surface.**
- **One adapter = hypothetical seam. Two adapters = real seam.**

The skill is informed by the project's domain model. The domain language names good seams; ADRs record decisions the skill should not re-litigate.

## Process

### 1. Explore

Ground in the project's documentation first — its established domain vocabulary and recorded decisions, as the in-context project `CLAUDE.md` points to them. With none present, proceed on the code alone.

Then walk the codebase — above ~25 files in scope, fan out `Explore` subagents (one per area) so the reads stay out of the main window; at or below that, explore inline (see [../DELEGATION.md](../DELEGATION.md)). Don't follow rigid heuristics — explore organically and note where you experience friction:

- Where does understanding one concept require bouncing between many small modules?
- Where are modules **shallow** — interface nearly as complex as the implementation?
- Where have pure functions been extracted just for testability, but the real bugs hide in how they're called (no **locality**)?
- Where do tightly-coupled modules leak across their seams?
- Which parts of the codebase are untested, or hard to test through their current interface?

Apply the **deletion test** to anything you suspect is shallow: would deleting it concentrate complexity, or just move it? A "yes, concentrates" is the signal you want.

### 2. Present candidates as an HTML report

Write a self-contained HTML file to the OS temp directory so nothing lands in the repo. Resolve the temp dir from `$TMPDIR`, falling back to `/tmp`, and write to `<tmpdir>/architecture-review-<timestamp>.html` so each run gets a fresh file. Open it for the user — `xdg-open <path>` on Linux, `open <path>` on macOS — and tell them the absolute path.

The report uses **Tailwind via CDN** for layout and styling, and **Mermaid via CDN** for diagrams where a graph/flow/sequence communicates the structure. Mix Mermaid with hand-crafted CSS/SVG visuals — Mermaid when relationships are graph-shaped (call graphs, dependencies, sequences), hand-built divs/SVG for editorial visuals (mass diagrams, cross-sections, collapse animations). Each candidate gets a **before/after visualisation**. Be visual.

Each candidate renders as a card:

- **Files** — which files/modules are involved
- **Problem** — why the current architecture is causing friction
- **Solution** — plain English description of what would change
- **Benefits** — explained in terms of locality and leverage, and how tests would improve
- **Before / After diagram** — side-by-side, custom-drawn, illustrating the shallowness and the deepening
- **Recommendation strength** — one of `Strong`, `Worth exploring`, `Speculative`, rendered as a badge

End the report with a **Top recommendation** section: which candidate you'd tackle first and why.

**Use the project's domain vocabulary for the domain, and [LANGUAGE.md](LANGUAGE.md) vocabulary for the architecture.** If the project's documentation defines "Order," talk about "the Order intake module" — not "the FooBarHandler," and not "the Order service."

**ADR conflicts**: if a candidate contradicts an existing ADR, surface it only when the friction warrants revisiting the ADR. Mark it clearly in the card (e.g. a warning callout: _"contradicts ADR-0007 — but worth reopening because…"_). Don't list every theoretical refactor an ADR forbids.

See [HTML-REPORT.md](HTML-REPORT.md) for the full HTML scaffold, diagram patterns, and styling guidance.

Do NOT propose interfaces yet. After the file is written, ask the user: "Which of these would you like to explore?"

### 3. Hand the chosen candidate to `design`

`deepen` is a finder: it surfaces candidates and stops. The report is its standalone artifact — steps 1–2 produce it without `design` in the loop.

Once the user picks a candidate, invoke `/design` on it for the design conversation. `design` walks the design tree — constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive — sharpening fuzzy terminology as it goes and offering a load-bearing decision as an ADR inline (see [../contracts/adr.md](../contracts/adr.md)). Pass the candidate's files, problem, and proposed solution so `design` opens on the deepening rather than rediscovering it.

Un-picked candidates are rejected, not deferred. Leave them in the report as dead — they are not findings and have no onward path.

## Handover

Per [../HANDOVER.md](../HANDOVER.md). End an interactive run by rendering this row as one `AskUserQuestion`.

- **artifact:** architectural candidates + HTML report
- **default:** `design` — design the chosen candidate, sharpening terminology and offering an ADR inline
- **alternatives:** stop

**Interactive-only** (per [../HANDOVER.md](../HANDOVER.md)) — surfacing candidates ends in a pick the user must make; `auto` never enters it.

From krixon/skills, MIT.

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