Eight Translations of One Dispatch — A WebGPU Stack Source-Level Walkthrough

One `pass.dispatchWorkgroups()` call traverses eight translations before it reaches GPU silicon — JS → Blink WebIDL → Renderer Wire → Mojo IPC → Dawn validation → Tint(WGSL→SPIR-V/MSL/HLSL) → Metal/D3D12/Vulkan → driver ISA. A 25-chapter vertical dissection of the full WebGPU stack — Dawn + wgpu side by side, real source, real latencies, threaded by a compute matmul.