How do you type async functions and Promises?

Question presented to candidate: "How do you type async functions and Promises in TypeScript? Walk me through return types, errors, and running several promises at once — and tell me which async bugs the compiler will not catch."

What a strong answer should cover:

• An async function always returns Promise<T>: annotate Promise<User> (annotating User is error TS1064), Promise<void> when nothing useful is returned; plain returned values are wrapped
• new Promise<T>(...) needs its type argument or the value is unknown; callback types say () => Promise<T>; Awaited and ReturnType derive types from existing async functions
• Errors are untyped: Promise<T> has no error parameter, a catch (err) variable is unknown under strict (TypeScript 4.4+), but .catch and allSettled reasons are any
• Concurrency: Promise.all on an array literal gives a typed tuple, allSettled results narrow on status, race with a Promise<never> timeout keeps the result type
• Bugs tsc does not flag: async callbacks passed to forEach, floating promises, return without await inside try — lint rules like no-floating-promises cover some of them

Clarifying questions expected:

• Should independent calls run in parallel or one after another?
• Is strict (or useUnknownInCatchVariables) on, and is type-aware linting part of the toolchain?

Code / implementation expected: Yes — a typed async function with error handling, and a Promise.all or allSettled call.