Fix potential goroutine leak in monitorStdin

Add a done channel to ensure the background goroutine that closes stdin exits cleanly when monitorStdin returns, not only when the context is cancelled. This prevents the goroutine from leaking if stdin closes before context cancellation.

Fixes #1664

Assisted-By: cagent

Author: dgageot

cmd/root/api.go

@@ -56,18 +56,26 @@ func newAPICmd() *cobra.Command {
 
 // monitorStdin monitors stdin for EOF, which indicates the parent process has died.
 // When spawned with piped stdio, stdin closes when the parent process dies.
+// The caller is responsible for cancelling the context (e.g. via defer cancel()).
 func monitorStdin(ctx context.Context, cancel context.CancelFunc, stdin *os.File) {
-	// Close stdin when context is cancelled to unblock the read
+	done := make(chan struct{})
+
+	// Close stdin when context is cancelled to unblock the read.
+	// Also exits cleanly when monitorStdin returns.
 	go func() {
-		<-ctx.Done()
+		select {
+		case <-ctx.Done():
+		case <-done:
+		}
 		stdin.Close()
 	}()
 
+	defer close(done)
+
 	buf := make([]byte, 1)
 	for {
 		n, err := stdin.Read(buf)
 		if err != nil || n == 0 {
-			// Only log and cancel if context isn't already done (parent died)
 			if ctx.Err() == nil {
 				slog.Info("stdin closed, parent process likely died, shutting down")
 				cancel()