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. Load codebase-design, the domain glossary, and applicable ADRs before scanning.

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 (CONTEXT.md) and any ADRs in the area you're touching first.

Then delegate a bounded codebase exploration to a subagent. 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 each candidate.

2. Present candidates as an HTML report

Render and open the candidate report through HTML-REPORT.md.

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

3. Grilling loop

Once the user picks a candidate, use grill-with-docs as an output-only planning session to walk its constraints, dependencies, module shape, seam, and surviving tests. Keep its returned deltas with the selected idea for the specification flow:

• Naming a proposed deepened module after a concept not in CONTEXT.md? Return the complete proposed glossary delta without presenting the future module as current truth.
• Sharpening a fuzzy term during the conversation? Preserve the complete clarified-language delta for the subsequent planning flow.
• User rejects the candidate with a load-bearing reason? Offer an ADR, framed as: "Want me to record this as an ADR so future architecture reviews don't re-suggest it?" Only that explicit approval grants domain-modeling canonical capture limited to the routed ADR. Skip ephemeral reasons ("not worth it right now") and self-evident ones.
• Want to explore alternative interfaces for the deepened module? Use the codebase-design skill and its design-it-twice parallel sub-agent pattern.