Time to build the real thing. The script writes a 3-record JSONL eval set; your job is the function that receipts it.
Write manifest_entry(path): read the file's bytes once, and return
a dict with three keys — file (the filename via path.name),
rows (the newline count — JSONL has no header, one record per
line), and sha256 (the first 8 characters of the content hash).
Expected output:
{"file": "eval.jsonl", "rows": 3, "sha256": "ed111c1a"}