Maintain a provenance-aware nutrition and fitness ledger in ChatGPT Library. Log food, hydration, and weight; correct entries without losing history; generate deterministic daily reports; and reconcile workout and activity snapshots without silently combining conflicting sources. Missing nutrient values remain unknown rather than becoming fabricated zeroes. Fitness Ledger is skills-only: it has no publisher-hosted service, telemetry, or required external account. It supports personal tracking and explanation, not medical diagnosis or treatment.