📝 **Task:** Implement `FileCache` with two methods: * `upload_or_reuse(content: bytes) -> str` — returns a `file_id`. If `sha256(content)` was seen before, return the cached id. Otherwise call `self._real_upload(content)` (already provided — it returns `f"file_{n}"` where `n` is the call count starting at 1) and remember the mapping. * `stats() -> tuple[int, int]` — returns `(uploads_called, cache_hits)`. The starter ends with a canonical driver: 2 distinct uploads + 1 duplicate. Expected canonical output: ``` file_1 file_2 file_1 (2, 1) ``` Two additional graded scenarios run after your code (via `input_append`) and exercise the empty-bytes and hot-doc boundaries — your `FileCache` must generalise so they pass too. 📋 Implement the function above. Tests run automatically. 💡 **Hint:** Re-read the theory if stuck.