skills: Add /improve-codebase

.claude/skills/improve-codebase/SKILL.md

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+---
+name: improve-codebase
+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
+
+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 its terms exactly in every suggestion, per its glossary.
+- The domain language in `.claude/CONTEXT.md` gives names to good seams; ADRs in `.claude/adr/` record decisions this command should not re-litigate.
+
+## Process
+
+### 1. Explore
+
+Read the project's domain glossary (`.claude/CONTEXT.md`) and any ADRs in the area you're touching first.
+
+Then use the Agent tool with `subagent_type=Explore` to walk every top-level module or directory in scope (the whole repository, or the area the user pointed you to) — even if only briefly for the ones that turn out clean. Within each, judge friction organically rather than against a rigid checklist:
+
+- 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.
+
+Zero candidates is a legitimate outcome for a genuinely clean area — but it has to follow from having looked, not from stopping early.
+
+### 2. Present candidates as an HTML report
+
+Write a self-contained HTML file to the OS temp directory so nothing lands in the repository. 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. Treat the open as best-effort: it's a no-op in a headless/sandboxed environment with no display server, so report the absolute path regardless of whether the open succeeded.
+
+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 `.claude/CONTEXT.md` vocabulary for the domain, and the `/codebase-design` vocabulary for the architecture.** If `.claude/CONTEXT.md` 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, only surface it when the friction is real enough to warrant 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. Grilling loop
+
+Once the user picks a candidate, run `/grill` 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 `/domain-modeling` to keep the domain model current as you go, even if `.claude/CONTEXT.md` doesn't exist yet:
+
+- **Naming a deepened module after a concept not in `.claude/CONTEXT.md`?** Add the term to `.claude/CONTEXT.md`. Create the file lazily if it doesn't exist.
+- **Sharpening a fuzzy term during the conversation?** Update `.claude/CONTEXT.md` right there.
+- **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 offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing — skip ephemeral reasons ("not worth it right now") 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.