TypeScript patterns

Follow the repo's tsconfig and lint config. Rules that matter most:

• External data (HTTP, JSON.parse, env, storage, LLM output) is unknown until parsed by the repo's schema library. Infer the type from the schema.
• No any, @ts-ignore, or as casts to silence errors. A cast is allowed only after a runtime check, with a comment naming it.
• Model states as discriminated unions with an exhaustive never check, not optional fields.
• Throw Error subclasses, never strings. No empty catch. No floating promises.
• Add a generic parameter only when it relates two positions.
• Use import type for type-only imports. No enum, no barrel files outside a package entry point.
• Share one schema between client and server instead of redeclaring types.