Normalize a Change-Directory Path

Question

Implement the path-resolution part of a shell `cd` command.

```python
def cd(cwd: str, dest: str) -> str: ...
```

## Requirements

- `cwd` is an absolute normalized path.
- An absolute `dest` starts from `/`; a relative destination starts from `cwd`.
- Ignore empty components and `.`.
- `..` removes one component but never moves above `/`.
- Collapse repeated slashes, remove trailing slashes except for root, and keep `/` as `/`.
- Treat names literally; filesystem existence and permissions are outside the first stage.

Examples should cover root, nested parents, absolute destinations, repeated separators, and names containing dots that are not exactly `.` or `..`.

## Follow-ups

1. Expand `~` and environment variables with explicit security rules.
2. Resolve symbolic links and explain logical versus physical `..` semantics.
3. Consult a filesystem interface for missing paths and permissions.
4. Explain why changing directory must be implemented by the shell process.