Design cleanup — make the tree read as designed-this-way

Why this skill exists

When a design decision changes mid-work — a different approach, a renamed concept, a replaced mechanism — the branch tends to keep fossils of the abandoned design: dead branches, shims that only served the old path, names shaped by the old concept, comments narrating the change, tests pinning behavior that no longer matters. The diff may show the journey; the final tree must not. This skill hunts those fossils down and rewrites the result as if the current design had been there from the beginning.

Step 1 — Establish the decision

State the decision as one line: "the design is X; the abandoned approach was Y". Take it from the user or the session context. If it is not stated, reconstruct it from the branch diff and commit messages, then confirm the one-line summary with the user before making sweeping edits — cleanup against a misread decision destroys correct code.

Step 2 — Determine scope

• Compute the branch diff: git diff $(git merge-base HEAD origin/main)...HEAD (fall back to origin/develop, then develop).
• The cleanup covers only code touched by the decision: the changed files that implement it, plus files that reference the renamed or removed concepts (find them by grepping for the old names).
• Everything else is out of bounds. This skill is not a license for unrelated refactors, formatting passes, or opportunistic improvements.

Step 3 — Hunt the leftovers

Check each category against the in-scope files:

• Dead code: branches, parameters, feature flags, config keys, and helpers that only the abandoned path used.
• Shims and indirection: adapters, wrappers, and abstraction layers that existed only to bridge the old design to the new one.
• Names and structure: identifiers, files, and modules shaped by the old concept — newParser, handleV2, legacyFoo, or a module layout organized around a concept that no longer exists.
• Comments and docstrings: anything describing the old design or narrating the change — "previously", "instead of", "now we", "changed from X to Y". Descriptions must state only the current design.
• Tests: tests that pin the abandoned behavior, transitional states, or the shape of the old API. Rewrite them for the intended behavior of the current design; do not keep them green by accident.
• Docs: README sections, ADRs, diagrams, and examples that describe the old mechanism. Update in place — no "migration note" additions.
• TODOs: items left for the old plan.

Step 4 — Rewrite, don't patch

• Rename to the current concept everywhere, not just where it is cheap.
• Delete dead code outright; never comment it out or gate it "just in case". Git history holds the old version.
• Collapse indirection that no longer earns its keep.
• Rewrite affected comments, docstrings, and docs to describe only the current state.

Step 5 — Verify and report

• Run the project's build and tests; the cleanup must not change behavior of the surviving design.
• Grep the resulting branch diff for history words as a smoke check: previously|instead of|no longer|old |new |V2|legacy — hits are candidates to fix, not automatic violations; judge each.
• Grep the whole tree for the abandoned names to confirm no dangling references remain.
• Report what was removed, renamed, and rewritten, grouped by the categories above, and call out anything suspicious that was left alone because it fell outside the decision's scope.