What is ReadonlyArray and readonly tuple?

Question presented to candidate: "What are ReadonlyArray and readonly tuples in TypeScript? How do they behave when you pass them to functions, and do they actually stop the array from changing?"

What a strong answer should cover:

• ReadonlyArray<T>, readonly T[] and Readonly<T[]> are the same type: an array view with no mutating methods (push, sort, splice), no index writes and a read-only length
• readonly [A, B] combines a tuple's fixed positions with the same read-only rules; as const on an array literal produces one
• Assignability is one-way: a mutable array can be passed where a readonly one is expected, but not the reverse ('readonly' and cannot be assigned to the mutable type)
• API design: accept readonly T[] parameters so callers can pass both kinds, and constrain generics with readonly unknown[]
• It is compile-time only: the run-time value is an ordinary array, a mutable alias can still change it, and Object.freeze is the run-time counterpart
• Version facts: the readonly T[] syntax, readonly tuples and as const arrived in TypeScript 3.4

Code / implementation expected: Optional — a function taking readonly number[], plus one rejected push or index assignment.