feat(poc): complete terrors PoC with main scenarios

server/crates/arbiter-terrors-poc/src/main.rs

@@ -1,5 +1,26 @@
-mod errors;
-mod db;
 mod auth;
+mod db;
+mod errors;
 
-fn main() {}
+use errors::ProtoError;
+
+fn run(id: u32, sig: &str) {
+    print!("authenticate(id={id}, sig={sig:?}) => ");
+    match auth::authenticate(id, sig) {
+        Ok(nonce) => println!("Ok(nonce={nonce})"),
+        Err(e) => match e.narrow::<errors::NotRegistered, _>() {
+            Ok(_) => println!("Err(NotRegistered) — handled locally"),
+            Err(remaining) => {
+                let proto = ProtoError::from(remaining);
+                println!("Err(ProtoError::{proto:?}) — forwarded to wire");
+            }
+        },
+    }
+}
+
+fn main() {
+    run(0, "ok");          // NotRegistered
+    run(1, "bad");         // InvalidSignature
+    run(99, "ok");         // Internal
+    run(1, "ok");          // success
+}