remote server: Do not spawn server when proxy reconnects (#18864)

This ensures that we only ever reconnect to a running server and not
spawn a new server with no state.

This avoids the problem of the server process crashing, `proxy`
reconnecting, starting a new server, and the user getting errors like
"unknown buffer id: ...".

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>

crates/remote_server/src/main.rs

@@ -24,6 +24,8 @@ enum Commands {
         stdout_socket: PathBuf,
     },
     Proxy {
+        #[arg(long)]
+        reconnect: bool,
         #[arg(long)]
         identifier: String,
     },
@@ -37,6 +39,7 @@ fn main() {
 
 #[cfg(not(windows))]
 fn main() -> Result<()> {
+    use remote::proxy::ProxyLaunchError;
     use remote_server::unix::{execute_proxy, execute_run, init};
 
     let cli = Cli::parse();
@@ -51,9 +54,20 @@ fn main() -> Result<()> {
             init(Some(log_file))?;
             execute_run(pid_file, stdin_socket, stdout_socket)
         }
-        Some(Commands::Proxy { identifier }) => {
+        Some(Commands::Proxy {
+            identifier,
+            reconnect,
+        }) => {
             init(None)?;
-            execute_proxy(identifier)
+            match execute_proxy(identifier, reconnect) {
+                Ok(_) => Ok(()),
+                Err(err) => {
+                    if let Some(err) = err.downcast_ref::<ProxyLaunchError>() {
+                        std::process::exit(err.to_exit_code());
+                    }
+                    Err(err)
+                }
+            }
         }
         Some(Commands::Version) => {
             eprintln!("{}", env!("ZED_PKG_VERSION"));