This problem requires the implementation of a standard Last-In-First-Out (LIFO) stack capable of processing a high volume of operations efficiently. The solution must handle multiple independent test cases.

Core Functional Requirements

The data structure must support the following commands:

• push(x): Append an integer x to the top of the stack.
• pop(): Remove the top element. If the structure is empty, output "Empty".
• query(): Inspect the top element without removal. If the structure is empty, output "Anguei!".
• size(): Return the current number of elements in the structure.

Performance Considerations

Given the constraints where the total number of operations can reach $10^6$, standard input/output methods in C++ may become a bottleneck. It is critical to disable synchronization with the C standard libraries to achieve acceptable performance.

C++ Implementation

The following code utilizes the STL std::stack adapter. By declaring the stack instance within the test case loop, memory is automatically reset or reused, satisfying the requirement to start with an empty stack for each dataset.

#include <iostream>
#include <stack>
#include <string>

// Optimization for high-speed I/O
void accelerate_io() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

int main() {
    accelerate_io();
    
    int test_cases;
    if (!(std::cin >> test_cases)) return 0;

    while (test_cases--) {
        std::stack<long long> buffer;
        int op_count;
        std::cin >> op_count;

        while (op_count--) {
            std::string operation;
            std::cin >> operation;

            if (operation == "push") {
                long long value;
                std::cin >> value;
                buffer.push(value);
            } 
            else if (operation == "pop") {
                if (buffer.empty()) {
                    std::cout << "Empty\n";
                } else {
                    buffer.pop();
                }
            } 
            else if (operation == "query") {
                if (buffer.empty()) {
                    std::cout << "Anguei!\n";
                } else {
                    std::cout << buffer.top() << "\n";
                }
            } 
            else if (operation == "size") {
                std::cout << buffer.size() << "\n";
            }
        }
    }
    return 0;
}