User error protection asks how well the product prevents users from making errors, and how well it helps them recover. A measure relates errors prevented or recovered to the opportunities for error. Protection has two halves: prevention, through constraints and good defaults, and recovery, through confirmation, undo and clear messages. A measure built only on errors observed will miss the errors that were prevented, so the definition should say which half it covers. The population is the set of tasks where an error would matter, not every click. This is one of the most useful families in a procurement conversation because it turns a vague claim about being easy to use into a testable property.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.