fantasia-yagni

name	fantasia-yagni
description	YAGNI and minimal diffs inside Fantasia mandatory structure: reuse ladder, no unrequested features or deps, shortest change that passes gates. Apply when scoping work, reviewing bloat, or choosing reuse vs greenfield.

YAGNI — implementation discipline

When to follow

• New feature, refactor, or dependency choice
• User request sounds heavy — check reuse first
• Diff review: duplicate util, speculative abstraction, parallel pattern

Always-on rule: yagni.mdc. Precedence: other .cursor/rules/* and fantasia-* skills win on structure, tests, i18n, gates.

Ladder (summary)

1. Need build at all?
2. Already in codebase?
3. Stdlib / platform?
4. Installed package.json dep?
5. Minimum inside conventions — shortest diff passing dev scoped gate (dev-scoped-verify.mdc); full yarn testbatch:verify at commit/final cleanup

Trace real flow before picking rung. Mandatory two-level, types/, Vitest/Playwright/Storybook, neverthrow, line caps — not skippable for brevity.

Orthogonal to caveman

Layer	Rule / skill	Job
Replies	caveman-default.mdc, .agents/skills/caveman/	Terse agent prose
Code	yagni.mdc	Minimal correct implementation

Both can stay on. YAGNI does not replace caveman or cavemem hooks.

Links

• code-size-decomposition.mdc — fewer modules until line caps force split
• fa-two-level-architecture.mdc
• fantasia-dev-scoped-verify — default post-edit gate
• fantasia-testing — connected tests + full gate at ship