improve-codebase-architecture

name	improve-codebase-architecture
description	Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
disable-model-invocation	true

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 these terms exactly in every suggestion — don't drift into "component," "service," "API," or "boundary."
• 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

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

Then use the Agent tool with subagent_type=Explore 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 the architecture. If the project's domain language names an "Order," talk about "the Order intake module" — not "the FooBarHandler," and not "the Order service."

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 grill-questions 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.