fix: create cancellable context before client connection

Move cancellable context creation to the beginning of Run() so that
the entire server lifecycle, including the client connection, can be
properly cancelled. This allows graceful shutdown to interrupt the
connection phase if needed.

The signal handler is also set up earlier to ensure interrupts are
caught as soon as possible.

Addresses PR #50 review comment #5

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: janisz

internal/app/app.go

@@ -33,6 +33,20 @@ func Run(ctx context.Context, cfg *config.Config, stdin io.ReadCloser, stdout io
 	// Log full configuration with sensitive data redacted.
 	slog.Info("Configuration loaded successfully", "config", cfg.Redacted())
 
+	// Create a cancellable context for the entire server lifecycle
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	// Set up signal handling for graceful shutdown.
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
+
+	go func() {
+		<-sigChan
+		slog.Info("Received shutdown signal")
+		cancel()
+	}()
+
 	stackroxClient, err := client.NewClient(&cfg.Central)
 	if err != nil {
 		return errors.Wrap(err, "failed to create client")
@@ -46,20 +60,6 @@ func Run(ctx context.Context, cfg *config.Config, stdin io.ReadCloser, stdout io
 		return errors.Wrap(err, "failed to connect to central")
 	}
 
-	// Set up signal handling for graceful shutdown.
-	sigChan := make(chan os.Signal, 1)
-	signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
-
-	// Create a cancellable context from the input context
-	ctx, cancel := context.WithCancel(ctx)
-	defer cancel()
-
-	go func() {
-		<-sigChan
-		slog.Info("Received shutdown signal")
-		cancel()
-	}()
-
 	slog.Info("Starting StackRox MCP server")
 
 	return errors.Wrap(srv.Start(ctx, stdin, stdout), "failed to start server")