Function find_boolean_gate_input 

pub fn find_boolean_gate_input<'a>(
    inputs: &'a [StackInputDefinition],
    input_id: &str,
) -> Result<&'a StackInputDefinition, GateInputIssue>

Finds the boolean deployer input a gate references, for render-time re-validation. The compile-time preflight enforces the same two rules; generators repeat them so a caller that renders without preflights cannot ship a template whose gate variable is undeclared or non-boolean.