Flatten Object

Requirements

• Accept a finite, acyclic object tree made of plain records (including null-prototype records), arrays, and primitive values. The root is always a record.
• Input keys are non-empty strings that do not contain dots, so dot-separated paths are unambiguous. Dates, class instances, functions, getters, proxies, and cycles are outside this exercise.
• Recursively flatten non-empty nested records, joining their property names with a dot. Keep top-level leaf keys unchanged.
• Visit only own enumerable string properties. Ignore inherited, non-enumerable, and symbol properties.
• Preserve numbers, strings, booleans, null, and explicit undefined without coercion or dropping falsy values.
• Treat arrays as leaf values, even if they contain objects or arrays. Preserve their references rather than flattening or cloning them.
• Preserve empty nested records at their paths and retain their references. An empty root returns a new empty object.
• Return a new ordinary object and never mutate the input. Shared nested objects may appear at multiple paths and must be flattened at every path.
• Handle names such as __proto__, constructor, and hasOwnProperty as ordinary own data properties without changing the output prototype.
• Use TypeScript Record<string, unknown> for input and output. You do not need to compute dot-path types at compile time.

Examples

Input: { user: { name: "Ada", address: { city: "Pune" } } }
Output: { "user.name": "Ada", "user.address.city": "Pune" }

Input: { settings: {}, items: [1, 2], active: false }
Output: { settings: {}, items: [1, 2], active: false }

Input: {}
Output: {}