Modern TypeScript conventions for library-agnostic code — strict mode, naming, type annotations, the type system (generics, utility types, conditional and mapped types), discriminated unions, error handling, async patterns, immutability, and project structure. Use when the user asks to "write TypeScript code", "create a TypeScript module", "define TypeScript types", "add type annotations", "use generics", "handle errors in TypeScript", "set up tsconfig" or "organize a TypeScript project", or whenever writing any TypeScript that is not tied to a specific library or framework. Does not cover React or other UI frameworks (react-best-practices, react-feature-sliced-design), CLI packaging and npm publishing (npx-package), plain JavaScript with no types, or service-specific APIs such as DynamoDB (aws-dynamodb-best-practices).