بازساخت کد به یک الگوی مشخص

Refactor the code below to use the [pattern name]
pattern. Constraints:

- Public API of the module must not change.
- All tests in [test file path] must still pass.
- Add brief inline comments only where the pattern is
  non-obvious to a reader who doesn't know it.
- Show the diff first, then a 3-line summary of why the
  refactor is worth it.

Original:
```
[paste code]
```