IStoreManager pattern
IStoreManager is the only layer in sr3e allowed to talk to Foundry's actor/item/effect APIs. Svelte components never call document.update() — they read and write through a store returned by StoreManager.Instance, and the singleton keeps that store in sync with the underlying document via Foundry hooks.
Localization scaffolding
lang/*.json files are generated, not hand-maintained. Every key that exists there comes from a TypeScript declaration under lang/config/. A Vite plugin watches those declarations and keeps the JSON in sync — you declare a key once, in TypeScript, and never touch the JSON structure yourself.