pub fn validate(step: &ComputerAct, tool: &str) -> Result<(), String>Expand description
Semantic-step validation: an element target (selector + exactly one
app scope) and the action’s payload.
tool names the calling pipeline in the error messages, so a future
consumer reports its own name instead of a hardcoded one.
§Errors
Returns Err for a missing/blank selector, name and pid
together, no app scope at all, a 0-based nth, or a missing payload —
set_value/type_text/perform_action need value,
set_numeric_value needs numeric_value, select_text needs a
well-formed range (exactly two numbers, start <= end).