Function invoke_op 

pub fn invoke_op(
    cx: &mut Cx,
    target: Value,
    key: &OpKey,
    input: Value,
) -> Result<Step>

Resolves and runs an operation on target, enforcing its OpSpec.

This is the kernel dispatch entry point: it resolves the key against the target (native Op or synthesized adapter), demands the required capabilities, checks the input against the declared args shape when that shape is registered, and then invokes the operation.