Game Sprite Pipeline

Local-first AI sprite generation. One skill, four modes behind --mode:

• portrait — single full-body character PNG (road-to-aew wrestlers, card-game characters).
• portrait-loop — 2×2 = 4-frame subtle idle (breathing + blink) at 200ms/frame in ONE Codex call. Animated portraits without re-prompting new poses.
• spritesheet — animated multi-frame grid with connected-components detection, ground-line anchor alignment, and Phaser atlas output.
• spritesheet --per-row — row-strip generation: each animation state generated as a separate strip with layout guide grounding and identity lock, then composited into a final sheet. Eliminates cross-row contamination and reduces retry scope from whole-sheet to single-row.

Backend chain (per ADR-198): Codex CLI imagegen is the default when installed and authed. When Codex is unavailable AND GEMINI_API_KEY (or GOOGLE_API_KEY) is set, the skill falls back to Nano Banana via nano-banana-builder's scripts. When neither is available, the skill fails loud with BackendUnavailableError listing both fix paths. Both paths use keys the user already holds — there is no third-party billing the toolkit hides. Reference implementation of the "Local-First, Deterministic Systems Over External APIs" principle in docs/PHILOSOPHY.md (user-owned-key clause).

When to use