improve-codebase-architecture

name	improve-codebase-architecture
description	Explore codebase for architectural improvement. Focus testability via deepening shallow modules. Use when user want improve architecture, find refactoring opportunities, consolidate tightly-coupled modules, or make codebase more AI-navigable.

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.

This skill is informed by the project's domain model. The domain glossary names good seams; ADRs in the area record decisions the skill should not re-litigate. Read both before exploring.

Use LANGUAGE.md vocabulary exactly: module, interface, implementation, depth, deep, shallow, seam, adapter, leverage, locality. Do not drift into "component," "service," "API," or "boundary."

Key principles:

• Deletion test: deleting a shallow module makes complexity vanish; deleting a deep module spreads complexity across callers.
• The interface is the test surface.
• One adapter means a hypothetical seam. Two adapters means a real seam.

Process

1. Explore

Read the project's domain glossary and any ADRs in the area you're touching first.

Use Agent(subagent_type=Explore) when available. Otherwise explore with rg, find, tests, and call graph reading. Look for:

• One concept require bouncing between many files?
• Shallow modules: interface nearly as complex as implementation?
• Pure functions extracted for testability, but real bugs hide in how called (no locality)?
• Tightly-coupled modules leaking across seams?
• Untested or hard-to-test areas?

Apply the deletion test to anything that looks shallow.

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 temp dir from $TMPDIR, falling back to /tmp (or %TEMP% on Windows), and write to <tmpdir>/architecture-review-<timestamp>.html so each run gets a fresh file. Open it for the user (open, xdg-open, or start) and tell them the absolute path.

Use Tailwind via CDN and Mermaid via CDN. Mix Mermaid with hand-crafted CSS/SVG visuals. Each candidate gets a before/after visualization. See HTML-REPORT.md for scaffold, diagram patterns, styling, and tone.

For each candidate card:

• Files/modules involved
• Problem: why current architecture causes friction
• Solution: what changes
• Benefits in terms of locality, leverage, and tests
• Before/after diagram showing shallowness vs deepening
• Recommendation strength: Strong, Worth exploring, or Speculative

Use LANGUAGE.md vocabulary for architecture and the project's CONTEXT.md vocabulary for the domain. If a candidate contradicts an existing ADR, only surface it when friction is real enough to warrant revisiting the ADR. Mark it clearly.

Do not propose interfaces yet. After writing the report, ask: "Which of these would you like to explore?"

3. Grilling loop

Once the user picks a candidate, drop into a grilling conversation. Walk the design tree: constraints, dependencies, shape of the deepened module, what sits behind the seam, what tests survive.

Side effects happen inline as decisions crystallize:

• Naming a deepened module after a concept not in CONTEXT.md? Add the term to CONTEXT.md. Create the file lazily if missing. See ../domain-model/CONTEXT-FORMAT.md.
• Sharpening a fuzzy term? Update CONTEXT.md right there.
• User rejects the candidate for a load-bearing reason? Offer an ADR so future architecture reviews do not re-suggest it. See ../domain-model/ADR-FORMAT.md.
• Want alternative interfaces? Use ../design-an-interface/SKILL.md.

4. Create GitHub Issue

Refactor RFC. See REFERENCE.md for template and dependency categories.