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.

This command is informed by the project's domain model and 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 those terms for architectural roles without renaming established domain concepts or framework constructs such as services, components, APIs, or boundaries; explain the mapping when it is not obvious.
• If the project keeps a domain glossary or domain docs, the language there gives names to good seams; any recorded design decisions cover ground this command should not re-litigate. This repo uses no fixed CONTEXT.md/docs/adr/ layout, so treat these as "if present" rather than required.

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 module, subsystem, or pain point, take that direction and skip the inference below.
• Otherwise, inspect a good stretch of recent commit history to find paths that keep changing and start there. If the changes are scattered with no clear hot spot, widen the net.

If the project keeps a domain glossary, domain docs, or recorded design decisions, read the ones covering the area you're touching first.

Then spawn a sub-agent to walk the codebase. 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 (or %TEMP% on Windows), 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, start <path> on Windows — 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 reliably communicates the structure. Mix Mermaid with hand-crafted CSS/SVG visuals — use Mermaid when relationships are graph-shaped (call graphs, dependencies, sequences), and hand-built divs/SVG when you want something more editorial (mass diagrams, cross-sections, collapse animations). Each candidate gets a before/after visualisation. Be visual.

For each candidate, render a card with:

• 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 own domain vocabulary for the domain (from its glossary or domain docs, if it keeps one), and the /codebase-design vocabulary for architectural roles. If the project calls a concept the "Order service," keep that name and describe its architectural role precisely, for example: "the Order service is a shallow module whose interface leaks persistence details."

Recorded-decision conflicts: if a candidate contradicts a design decision the project has already recorded, only surface it when the friction is real enough to warrant revisiting that decision. Mark it clearly in the card (e.g. a warning callout: "contradicts a recorded decision — but worth reopening because…"). Don't list every theoretical refactor a past decision forbids.

See 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. Grilling loop

Once the user picks a candidate, run the grilling skill (/grill) at Full intensity to walk the design tree with them — constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive.

Side effects happen inline as decisions crystallize — run the /domain-modeling skill to keep the domain model current as you go:

• Naming a deepened module after a concept the project's domain docs don't cover? Record the term wherever the project keeps its domain vocabulary, if it keeps one. Don't stand up a glossary the project hasn't asked for.
• Sharpening a fuzzy term during the conversation? Capture it in the same place, right there.
• User rejects the candidate with a load-bearing reason? Offer to record the decision, framed as: "Want me to note this so architecture reviews don't re-suggest it?" Only offer when the reason would help another reviewer avoid re-suggesting the same thing; skip ephemeral reasons ("not worth it") and self-evident ones.
• Want to explore alternative interfaces for the deepened module? Run the /codebase-design skill and use its design-it-twice parallel sub-agent pattern.