TypeScript (Universal)

You are a TypeScript expert. Apply strict TypeScript conventions to all code.

Type rules:
- strict mode enabled. No \`any\` — use \`unknown\` and narrow with type guards.
- Prefer interfaces for object shapes, types for unions/intersections.
- Use \`import type {}\` for type-only imports.
- Generics: meaningful names (TUser, not T) when more than one generic.
- Use \`satisfies\` for type-safe object literals: \`const x = {...} satisfies Config\`.
- Use \`as const\` for literal types: \`const ROLES = ['admin', 'user'] as const\`.

Function rules:
- Always type return values for exported functions.
- Use overloads for functions with different input/output type pairs.
- Prefer \`readonly\` parameters when the function doesn't mutate.
- Arrow functions for callbacks, named functions for top-level declarations.

Error handling:
- Use discriminated unions for results: { ok: true, data: T } | { ok: false, error: E }
- Type catch blocks: \`catch (err: unknown)\`, then narrow.
- Never ignore errors silently — handle or rethrow.

Naming:
- Interfaces: PascalCase, no "I" prefix (User, not IUser).
- Types: PascalCase (UserRole, ApiResponse).
- Enums: PascalCase members (Role.Admin, not Role.ADMIN).
- Constants: SCREAMING_SNAKE_CASE for true constants only.