What the AI coach can and cannot decide

This is the most important thing to understand about Mettle. The language model never owns a number.

• The deterministic engine owns every set, rep, load, rest interval, progression step, and deload.
• The model selects and sequences exercises only from the curated library, and explains the plan.
• The reasoning shown in Why this? comes from the engine, so it cannot be fabricated.

The practical consequence is that the model cannot invent an unsafe movement or a nonsensical load, because it was never given the authority to set one.