Fix flakey SSH connection (#19439)

Fixes a bug due to the `select!` macro tossing futures that had
partially read messages, causing us to desync our message reading with
the input stream.

Release Notes:

- N/A

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: conrad <conrad@zed.dev>

crates/remote_server/src/unix.rs

@@ -12,6 +12,7 @@ use language::LanguageRegistry;
 use node_runtime::{NodeBinaryOptions, NodeRuntime};
 use paths::logs_dir;
 use project::project_settings::ProjectSettings;
+
 use remote::proxy::ProxyLaunchError;
 use remote::ssh_session::ChannelClient;
 use remote::{
@@ -213,19 +214,27 @@ fn start_server(
 
             let mut input_buffer = Vec::new();
             let mut output_buffer = Vec::new();
+
+            let (mut stdin_msg_tx, mut stdin_msg_rx) = mpsc::unbounded::<Envelope>();
+            cx.background_executor().spawn(async move {
+                while let Ok(msg) = read_message(&mut stdin_stream, &mut input_buffer).await {
+                    if let Err(_) = stdin_msg_tx.send(msg).await {
+                        break;
+                    }
+                }
+            }).detach();
+
             loop {
+
                 select_biased! {
                     _ = app_quit_rx.next().fuse() => {
                         return anyhow::Ok(());
                     }
 
-                    stdin_message = read_message(&mut stdin_stream, &mut input_buffer).fuse() => {
-                        let message = match stdin_message {
-                            Ok(message) => message,
-                            Err(error) => {
-                                log::warn!("error reading message on stdin: {}. exiting.", error);
-                                break;
-                            }
+                    stdin_message = stdin_msg_rx.next().fuse() => {
+                        let Some(message) = stdin_message else {
+                            log::warn!("error reading message on stdin. exiting.");
+                            break;
                         };
                         if let Err(error) = incoming_tx.unbounded_send(message) {
                             log::error!("failed to send message to application: {:?}. exiting.", error);