gRPC Streaming in Rust: The Four Patterns You Need to Know (with Tonic)

Let me paint you a picture. You're building a metrics dashboard. Every client needs live data — CPU usage, request rates, error counts, the works. So you do what everyone does: you set up a REST endpoint and poll it. Every second. Per client. Ten clients? Fine. A hundred? Starting to sweat. A thousand clients each hammering your /metrics endpoint every second? You've just built the world's most expensive busy-wait loop. Your server is spending most of its time answering "anything new?" with "n