Add readiness probe to devenv

devenv.nix

@@ -80,6 +80,11 @@ in
       ${config.outputs.server}/bin/server -config "$DEVENV_RUNTIME/metadata-config.yaml"
     '';
     after = [ "devenv:processes:postgres" ];
+    # Probes the standard gRPC Health Checking Protocol (cmd/server/main.go
+    # registers google.golang.org/grpc/health + reflection). Port matches
+    # server.port in the YAML above. SERVING means the gRPC server is
+    # accepting connections; postgres readiness is already gated by `after`.
+    ready.exec = "grpcurl -plaintext -max-time 2 localhost:50053 grpc.health.v1.Health/Check | grep -q SERVING";
   };
 
   outputs = {