interface-designlisted

# Interface Design ## Core Rule Generate radically different alternatives before converging. Compare on depth, locality, and seam placement — not aesthetics. ## Kit Context Before starting: 1. Read `CODEBASE_MAP.md` for project understanding 2. Read `CLAUDE.project.md` if it exists for project-specific rules 3. Read `agent_docs/architecture-language.md` — **required**. This skill speaks its vocabulary. 4. Read `tasks/decisions.md` — don't re-litigate ADR-resolved interface decisions. If `agent_docs/architecture-language.md` hasn't been read in this session, read it now. ## When to Use Invoke with `/interface-design <module>` when: - After `/deepening-review` settles on a deepening candidate and the user wants to see alternative interface shapes before committing - A new module is about to be created and the first interface idea feels under-explored - An existing interface is being rewritten and "design it once" feels insufficient - You catch yourself converging on the first plausible interface — that's exactly when this skill earns its keep Based on Ousterhout's *"Design It Twice"*: **your first interface idea is unlikely to be the best.** Spawning parallel agents with different constraints produces designs you wouldn't have reached by iterating sequentially on one. ## When NOT to Use - Trivial modules (a 3-line utility doesn't warrant 3 competing designs) - When the interface is dictated by an external contract (HTTP spec, protobuf, third-party SDK shape) — there