Steam: saves in a file, written safely, with a web-save import #161

Part of #142 · Milestone 3: Playable desktop build (Windows) · plan item 3.3

Size: M · Owner-only step: no · Blocks launch: yes

What

Saves live in localStorage today. The desktop game should write a file (so Steam Cloud can sync it), atomically (temp file then rename), keeping three rolling backups. Web players need a way to bring their save over.

Decision / recommendation

File saves + three backups; an "Import a web save" button for a file the web game can export.

Done when

• Kill the app mid-save: the game still loads
• A web save imports

Plan page (owner only): https://claude.ai/artifact/Cf5SWQHzAKTy2uHCC1UQgw