Frontend Optimistic Mutations (the write path)

Portable skill — readable by Claude Code, OpenCode, Codex, Cursor, Windsurf, and others. This skill describes the discipline of the write path — optimistic updates, rollback, idempotency, cache coherence — not a UI library or a styling system. It builds directly on the frontend-data-contracts skill (writes go through the typed client) and the frontend-architecture skill (mutations live in modules/{feature}/hooks/, keyed by a factory).

The goal: a write feels instant (the UI reflects it before the server confirms), is safe (a failure restores the exact prior state, and a retry never double-charges), and leaves the cache coherent (the detail view and every list page agree). All three at once — that's the craft.

0. The five core ideas