refactor(grpc): bind TCP listener before etcd registration to prevent connection issues

- Change tokio-stream dependency to include net feature for TcpListenerStream
- Move TCP listener binding before etcd registry initialization in main function
- Pass pre-bound TcpListener to gRPC server instead of just SocketAddr
- Update gRPC server to use serve_with_incoming with TcpListenerStream
- Prevent peers from attempting connections before gRPC server is ready
- Ensure proper error handling for TCP binding failures during startup

main.rs

@@ -37,6 +37,17 @@ async fn main() -> AppResult<()> {
     let cache = Arc::new(AppCache::from_config(&config).await?);
     let storage = AppS3Storage::from_config(&config).await?;
 
+    let rpc_host = config.get_env_or::<String>("APP_RPC_SELF_HOST", "0.0.0.0".to_string())?;
+    let rpc_port = config.get_env_or::<u16>("APP_RPC_SELF_PORT", 50050)?;
+    let rpc_addr: std::net::SocketAddr = format!("{rpc_host}:{rpc_port}").parse()
+        .map_err(|e| appks::error::AppError::Config(format!("invalid gRPC address: {e}")))?;
+
+    // Bind the TCP listener FIRST so the port is reserved before etcd registration.
+    // This prevents peers from trying to connect before the gRPC server is ready.
+    let rpc_listener = tokio::net::TcpListener::bind(rpc_addr)
+        .await
+        .map_err(|e| appks::error::AppError::Config(format!("gRPC bind failed on {rpc_addr}: {e}")))?;
+
     let registry = Arc::new(EtcdRegistry::connect(&config).await?);
     registry.start_discovery().await?;
     registry
@@ -57,13 +68,9 @@ async fn main() -> AppResult<()> {
     )
     .await;
 
-    let rpc_host = config.get_env_or::<String>("APP_RPC_SELF_HOST", "0.0.0.0".to_string())?;
-    let rpc_port = config.get_env_or::<u16>("APP_RPC_SELF_PORT", 50050)?;
-    let rpc_addr: std::net::SocketAddr = format!("{rpc_host}:{rpc_port}").parse()
-        .map_err(|e| appks::error::AppError::Config(format!("invalid gRPC address: {e}")))?;
     let grpc_service = service.clone();
     tokio::spawn(async move {
-        if let Err(e) = appks::grpc::start_grpc_server(rpc_addr, grpc_service).await {
+        if let Err(e) = appks::grpc::start_grpc_server(rpc_addr, rpc_listener, grpc_service).await {
             tracing::error!(error = %e, "gRPC server failed");
         }
     });