feat(grpc-nats-micro): bind annotated protobuf services to NATS micro

proto/trogonai/grpc_nats_micro/v1/echo.proto

@@ -0,0 +1,50 @@
+edition = "2024";
+
+// Reference service for the grpc-nats-micro binding (ADR 0016). It is the
+// conformance fixture the binding's integration tests drive, and a worked
+// example of a protobuf service annotated for NATS micro. It carries no domain
+// meaning.
+package trogonai.grpc_nats_micro.v1;
+
+import "google/rpc/code.proto";
+import "google/rpc/status.proto";
+import "trogon/nats/micro/v1alpha1/options.proto";
+
+// EchoService is the reference NATS micro service. The binding derives one
+// endpoint per rpc; success replies carry the response message, faults carry
+// a google.rpc.Status on the micro error channel (ADR 0016 section 3).
+service EchoService {
+  option (trogon.nats.micro.v1alpha1.service) = {version: "1.0.0"};
+
+  // Say returns the request message unchanged.
+  rpc Say(SayRequest) returns (SayResponse);
+
+  // Fail always faults, so tests can exercise the google.rpc.Status error
+  // channel. The requested code is echoed back as the fault's status code.
+  rpc Fail(FailRequest) returns (FailResponse) {
+    option (trogon.nats.micro.v1alpha1.method) = {
+      metadata: {
+        key: "always-faults"
+        value: "true"
+      }
+    };
+  }
+}
+
+message SayRequest {
+  string message = 1;
+}
+
+message SayResponse {
+  string message = 1;
+}
+
+message FailRequest {
+  // Canonical status code the handler should fault with.
+  google.rpc.Code code = 1;
+  string message = 2;
+}
+
+message FailResponse {
+  string message = 1;
+}