fix: subscribe to process channels before spawning threads to prevent event loss

Fast-exiting processes (e.g. echo) sent data/end events before
start() subscribed to the broadcast channels, causing the stream
to hang indefinitely and the exec RPC to time out with 502.

Move channel subscription into spawn_process, before reader/waiter
threads start, and return pre-subscribed receivers via SpawnedProcess.

envd-rs/src/main.rs

@@ -222,8 +222,8 @@ fn spawn_initial_command(cmd: &str, state: &AppState) {
         &user,
         &state.defaults.env_vars,
     ) {
-        Ok(handle) => {
-            tracing::info!(pid = handle.pid, cmd, "initial command spawned");
+        Ok(spawned) => {
+            tracing::info!(pid = spawned.handle.pid, cmd, "initial command spawned");
         }
         Err(e) => {
             tracing::error!(error = %e, cmd, "failed to spawn initial command");

envd-rs/src/rpc/process_handler.rs

@@ -128,6 +128,12 @@ impl ProcessHandle {
     }
 }
 
+pub struct SpawnedProcess {
+    pub handle: Arc<ProcessHandle>,
+    pub data_rx: broadcast::Receiver<DataEvent>,
+    pub end_rx: broadcast::Receiver<EndEvent>,
+}
+
 pub fn spawn_process(
     cmd_str: &str,
     args: &[String],
@@ -138,7 +144,7 @@ pub fn spawn_process(
     tag: Option<String>,
     user: &nix::unistd::User,
     default_env_vars: &dashmap::DashMap<String, String>,
-) -> Result<Arc<ProcessHandle>, ConnectError> {
+) -> Result<SpawnedProcess, ConnectError> {
     let mut env: Vec<(String, String)> = Vec::new();
     env.push(("PATH".into(), std::env::var("PATH").unwrap_or_default()));
     let home = user.dir.to_string_lossy().to_string();
@@ -248,6 +254,9 @@ pub fn spawn_process(
             pty_master: Mutex::new(Some(master_file)),
         });
 
+        let data_rx = handle.subscribe_data();
+        let end_rx = handle.subscribe_end();
+
         let data_tx_clone = data_tx.clone();
         std::thread::spawn(move || {
             let mut master = master_clone;
@@ -287,7 +296,7 @@ pub fn spawn_process(
         });
 
         tracing::info!(pid, cmd = cmd_str, "process started (pty)");
-        Ok(handle)
+        Ok(SpawnedProcess { handle, data_rx, end_rx })
     } else {
         let mut command = std::process::Command::new("/bin/sh");
         command
@@ -331,6 +340,9 @@ pub fn spawn_process(
             pty_master: Mutex::new(None),
         });
 
+        let data_rx = handle.subscribe_data();
+        let end_rx = handle.subscribe_end();
+
         if let Some(mut out) = stdout {
             let tx = data_tx.clone();
             std::thread::spawn(move || {
@@ -386,7 +398,7 @@ pub fn spawn_process(
         });
 
         tracing::info!(pid, cmd = cmd_str, "process started (pipe)");
-        Ok(handle)
+        Ok(SpawnedProcess { handle, data_rx, end_rx })
     }
 }
 

envd-rs/src/rpc/process_service.rs

@@ -66,7 +66,7 @@ impl ProcessServiceImpl {
     fn spawn_from_request(
         &self,
         request: &StartRequestView<'_>,
-    ) -> Result<Arc<ProcessHandle>, ConnectError> {
+    ) -> Result<process_handler::SpawnedProcess, ConnectError> {
         let proc_config = request.process.as_option().ok_or_else(|| {
             ConnectError::new(ErrorCode::InvalidArgument, "process config required")
         })?;
@@ -117,7 +117,7 @@ impl ProcessServiceImpl {
             "process.Start request"
         );
 
-        let handle = process_handler::spawn_process(
+        let spawned = process_handler::spawn_process(
             cmd,
             &args,
             &envs,
@@ -129,17 +129,17 @@ impl ProcessServiceImpl {
             &self.state.defaults.env_vars,
         )?;
 
-        self.processes.insert(handle.pid, Arc::clone(&handle));
+        self.processes.insert(spawned.handle.pid, Arc::clone(&spawned.handle));
 
         let processes = self.processes.clone();
-        let pid = handle.pid;
-        let mut end_rx = handle.subscribe_end();
+        let pid = spawned.handle.pid;
+        let mut cleanup_end_rx = spawned.handle.subscribe_end();
         tokio::spawn(async move {
-            let _ = end_rx.recv().await;
+            let _ = cleanup_end_rx.recv().await;
             processes.remove(&pid);
         });
 
-        Ok(handle)
+        Ok(spawned)
     }
 }
 
@@ -183,11 +183,11 @@ impl Process for ProcessServiceImpl {
         ),
         ConnectError,
     > {
-        let handle = self.spawn_from_request(&request)?;
-        let pid = handle.pid;
+        let spawned = self.spawn_from_request(&request)?;
+        let pid = spawned.handle.pid;
 
-        let mut data_rx = handle.subscribe_data();
-        let mut end_rx = handle.subscribe_end();
+        let mut data_rx = spawned.data_rx;
+        let mut end_rx = spawned.end_rx;
 
         let stream = async_stream::stream! {
             yield Ok(make_start_response(pid));