zig and gpu variants

// Test 820: Zig and GPU Variants Together
//
// Tests the fallback pattern: provide both Zig and GPU implementations.
// Emitter should emit the Zig variant and skip the GPU variant.
//
// This demonstrates graceful degradation:
// - If GPU compiler pass runs → Use GPU
// - If GPU compiler pass doesn't run → Use Zig fallback
//
// What this tests:
// ✅ Emitter emits compute|zig variant
// ✅ Emitter skips compute|gpu variant
// ✅ Both variants can coexist
// ✅ Zig variant provides working fallback

const std = @import("std");

~pub event compute {
    value: f32,
}
| done f32

// Zig implementation - always works
~proc compute|zig {
    return .{ .done = value * 2.0 };
}

// GPU implementation - requires compiler pass
~proc compute|gpu {
    #version 450

    layout(local_size_x = 1) in;

    layout(binding = 0) buffer Input {
        float value;
    } input_data;

    layout(binding = 1) buffer Output {
        float result;
    } output_data;

    void main() {
        output_data.result = input_data.value * 2.0;
    }
}