diff --git a/pkg/core/async_test.go b/pkg/core/async_test.go
new file mode 100644
index 0000000..f29ff9e
--- /dev/null
+++ b/pkg/core/async_test.go
@@ -0,0 +1,139 @@
+package core
+
+import (
+	"context"
+	"errors"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCore_PerformAsync_Good(t *testing.T) {
+	c, _ := New()
+	
+	var completed atomic.Bool
+	var resultReceived any
+	
+	c.RegisterAction(func(c *Core, msg Message) error {
+		if tc, ok := msg.(ActionTaskCompleted); ok {
+			resultReceived = tc.Result
+			completed.Store(true)
+		}
+		return nil
+	})
+	
+	c.RegisterTask(func(c *Core, task Task) (any, bool, error) {
+		return "async-result", true, nil
+	})
+	
+	taskID := c.PerformAsync(TestTask{})
+	assert.NotEmpty(t, taskID)
+	
+	// Wait for completion
+	assert.Eventually(t, func() bool {
+		return completed.Load()
+	}, 1*time.Second, 10*time.Millisecond)
+	
+	assert.Equal(t, "async-result", resultReceived)
+}
+
+func TestCore_PerformAsync_Shutdown(t *testing.T) {
+	c, _ := New()
+	_ = c.ServiceShutdown(context.Background())
+	
+	taskID := c.PerformAsync(TestTask{})
+	assert.Empty(t, taskID, "PerformAsync should return empty string if already shut down")
+}
+
+func TestCore_Progress_Good(t *testing.T) {
+	c, _ := New()
+	
+	var progressReceived float64
+	var messageReceived string
+	
+	c.RegisterAction(func(c *Core, msg Message) error {
+		if tp, ok := msg.(ActionTaskProgress); ok {
+			progressReceived = tp.Progress
+			messageReceived = tp.Message
+		}
+		return nil
+	})
+	
+	c.Progress("task-1", 0.5, "halfway", TestTask{})
+	
+	assert.Equal(t, 0.5, progressReceived)
+	assert.Equal(t, "halfway", messageReceived)
+}
+
+func TestCore_WithService_UnnamedType(t *testing.T) {
+	// Primitive types have no package path
+	factory := func(c *Core) (any, error) {
+		s := "primitive"
+		return &s, nil
+	}
+	
+	_, err := New(WithService(factory))
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "service name could not be discovered")
+}
+
+func TestRuntime_ServiceStartup_ErrorPropagation(t *testing.T) {
+	rt, _ := NewRuntime(nil)
+	
+	// Register a service that fails startup
+	errSvc := &MockStartable{err: errors.New("startup failed")}
+	_ = rt.Core.RegisterService("error-svc", errSvc)
+	
+	err := rt.ServiceStartup(context.Background(), nil)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "startup failed")
+}
+
+func TestCore_ServiceStartup_ContextCancellation(t *testing.T) {
+	c, _ := New()
+	
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // Cancel immediately
+	
+	s1 := &MockStartable{}
+	_ = c.RegisterService("s1", s1)
+	
+	err := c.ServiceStartup(ctx, nil)
+	assert.Error(t, err)
+	assert.ErrorIs(t, err, context.Canceled)
+	assert.False(t, s1.started, "Service should not have started if context was cancelled before loop")
+}
+
+func TestCore_ServiceShutdown_ContextCancellation(t *testing.T) {
+	c, _ := New()
+	
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // Cancel immediately
+	
+	s1 := &MockStoppable{}
+	_ = c.RegisterService("s1", s1)
+	
+	err := c.ServiceShutdown(ctx)
+	assert.Error(t, err)
+	assert.ErrorIs(t, err, context.Canceled)
+	assert.False(t, s1.stopped, "Service should not have stopped if context was cancelled before loop")
+}
+
+type TaskWithIDImpl struct {
+	id string
+}
+func (t *TaskWithIDImpl) SetTaskID(id string) { t.id = id }
+func (t *TaskWithIDImpl) GetTaskID() string { return t.id }
+
+func TestCore_PerformAsync_InjectsID(t *testing.T) {
+	c, _ := New()
+	c.RegisterTask(func(c *Core, t Task) (any, bool, error) { return nil, true, nil })
+	
+	task := &TaskWithIDImpl{}
+	taskID := c.PerformAsync(task)
+	
+	assert.Equal(t, taskID, task.GetTaskID())
+}
diff --git a/pkg/core/core.go b/pkg/core/core.go
index a91d93c..eb7c64b 100644
--- a/pkg/core/core.go
+++ b/pkg/core/core.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"slices"
 	"strings"
 	"sync"
 )
@@ -65,6 +66,9 @@ func WithService(factory func(*Core) (any, error)) Option {
 		if err != nil {
 			return fmt.Errorf("core: failed to create service: %w", err)
 		}
+		if serviceInstance == nil {
+			return fmt.Errorf("core: service factory returned nil instance")
+		}
 
 		// --- Service Name Discovery ---
 		typeOfService := reflect.TypeOf(serviceInstance)
@@ -74,6 +78,9 @@ func WithService(factory func(*Core) (any, error)) Option {
 		pkgPath := typeOfService.PkgPath()
 		parts := strings.Split(pkgPath, "/")
 		name := strings.ToLower(parts[len(parts)-1])
+		if name == "" {
+			return fmt.Errorf("core: service name could not be discovered for type %T (PkgPath is empty)", serviceInstance)
+		}
 
 		// --- IPC Handler Discovery ---
 		instanceValue := reflect.ValueOf(serviceInstance)
@@ -81,6 +88,8 @@ func WithService(factory func(*Core) (any, error)) Option {
 		if handlerMethod.IsValid() {
 			if handler, ok := handlerMethod.Interface().(func(*Core, Message) error); ok {
 				c.RegisterAction(handler)
+			} else {
+				return fmt.Errorf("core: service %q has HandleIPCEvents but wrong signature; expected func(*Core, Message) error", name)
 			}
 		}
 
@@ -141,6 +150,9 @@ func (c *Core) ServiceStartup(ctx context.Context, options any) error {
 
 	var agg error
 	for _, s := range startables {
+		if err := ctx.Err(); err != nil {
+			return errors.Join(agg, err)
+		}
 		if err := s.OnStartup(ctx); err != nil {
 			agg = errors.Join(agg, err)
 		}
@@ -156,18 +168,36 @@ func (c *Core) ServiceStartup(ctx context.Context, options any) error {
 // ServiceShutdown is the entry point for the Core service's shutdown lifecycle.
 // It is called by the GUI runtime when the application shuts down.
 func (c *Core) ServiceShutdown(ctx context.Context) error {
+	c.shutdown.Store(true)
+
 	var agg error
 	if err := c.ACTION(ActionServiceShutdown{}); err != nil {
 		agg = errors.Join(agg, err)
 	}
 
 	stoppables := c.svc.getStoppables()
-	for i := len(stoppables) - 1; i >= 0; i-- {
-		if err := stoppables[i].OnShutdown(ctx); err != nil {
+	for _, s := range slices.Backward(stoppables) {
+		if err := ctx.Err(); err != nil {
+			agg = errors.Join(agg, err)
+			break // don't return — must still wait for background tasks below
+		}
+		if err := s.OnShutdown(ctx); err != nil {
 			agg = errors.Join(agg, err)
 		}
 	}
 
+	// Wait for background tasks (PerformAsync), respecting context deadline.
+	done := make(chan struct{})
+	go func() {
+		c.wg.Wait()
+		close(done)
+	}()
+	select {
+	case <-done:
+	case <-ctx.Done():
+		agg = errors.Join(agg, ctx.Err())
+	}
+
 	return agg
 }
 
@@ -209,6 +239,10 @@ func (c *Core) PERFORM(t Task) (any, bool, error) {
 // It returns a unique task ID that can be used to track the task's progress.
 // The result of the task will be broadcasted via an ActionTaskCompleted message.
 func (c *Core) PerformAsync(t Task) string {
+	if c.shutdown.Load() {
+		return ""
+	}
+
 	taskID := fmt.Sprintf("task-%d", c.taskIDCounter.Add(1))
 
 	// If the task supports it, inject the ID
@@ -222,7 +256,7 @@ func (c *Core) PerformAsync(t Task) string {
 		Task:   t,
 	})
 
-	go func() {
+	c.wg.Go(func() {
 		result, handled, err := c.PERFORM(t)
 		if !handled && err == nil {
 			err = fmt.Errorf("no handler found for task type %T", t)
@@ -235,7 +269,7 @@ func (c *Core) PerformAsync(t Task) string {
 			Result: result,
 			Error:  err,
 		})
-	}()
+	})
 
 	return taskID
 }
diff --git a/pkg/core/interfaces.go b/pkg/core/interfaces.go
index ee74b47..036b4b2 100644
--- a/pkg/core/interfaces.go
+++ b/pkg/core/interfaces.go
@@ -5,6 +5,7 @@ import (
 	"embed"
 	goio "io"
 	"slices"
+	"sync"
 	"sync/atomic"
 )
 
@@ -85,6 +86,8 @@ type Core struct {
 	bus      *messageBus
 
 	taskIDCounter atomic.Uint64
+	wg            sync.WaitGroup
+	shutdown      atomic.Bool
 }
 
 // Config provides access to application configuration.
diff --git a/pkg/core/message_bus.go b/pkg/core/message_bus.go
index 457ced2..4f81e77 100644
--- a/pkg/core/message_bus.go
+++ b/pkg/core/message_bus.go
@@ -2,6 +2,7 @@ package core
 
 import (
 	"errors"
+	"slices"
 	"sync"
 )
 
@@ -28,7 +29,7 @@ func newMessageBus(c *Core) *messageBus {
 // action dispatches a message to all registered IPC handlers.
 func (b *messageBus) action(msg Message) error {
 	b.ipcMu.RLock()
-	handlers := append([]func(*Core, Message) error(nil), b.ipcHandlers...)
+	handlers := slices.Clone(b.ipcHandlers)
 	b.ipcMu.RUnlock()
 
 	var agg error
@@ -57,7 +58,7 @@ func (b *messageBus) registerActions(handlers ...func(*Core, Message) error) {
 // query dispatches a query to handlers until one responds.
 func (b *messageBus) query(q Query) (any, bool, error) {
 	b.queryMu.RLock()
-	handlers := append([]QueryHandler(nil), b.queryHandlers...)
+	handlers := slices.Clone(b.queryHandlers)
 	b.queryMu.RUnlock()
 
 	for _, h := range handlers {
@@ -72,7 +73,7 @@ func (b *messageBus) query(q Query) (any, bool, error) {
 // queryAll dispatches a query to all handlers and collects all responses.
 func (b *messageBus) queryAll(q Query) ([]any, error) {
 	b.queryMu.RLock()
-	handlers := append([]QueryHandler(nil), b.queryHandlers...)
+	handlers := slices.Clone(b.queryHandlers)
 	b.queryMu.RUnlock()
 
 	var results []any
@@ -99,7 +100,7 @@ func (b *messageBus) registerQuery(handler QueryHandler) {
 // perform dispatches a task to handlers until one executes it.
 func (b *messageBus) perform(t Task) (any, bool, error) {
 	b.taskMu.RLock()
-	handlers := append([]TaskHandler(nil), b.taskHandlers...)
+	handlers := slices.Clone(b.taskHandlers)
 	b.taskMu.RUnlock()
 
 	for _, h := range handlers {
diff --git a/pkg/core/runtime_pkg.go b/pkg/core/runtime_pkg.go
index 0cb941d..7071e9c 100644
--- a/pkg/core/runtime_pkg.go
+++ b/pkg/core/runtime_pkg.go
@@ -3,7 +3,8 @@ package core
 import (
 	"context"
 	"fmt"
-	"sort"
+	"maps"
+	"slices"
 )
 
 // ServiceRuntime is a helper struct embedded in services to provide access to the core application.
@@ -58,14 +59,13 @@ func NewWithFactories(app any, factories map[string]ServiceFactory) (*Runtime, e
 		WithApp(app),
 	}
 
-	names := make([]string, 0, len(factories))
-	for name := range factories {
-		names = append(names, name)
-	}
-	sort.Strings(names)
+	names := slices.Sorted(maps.Keys(factories))
 
 	for _, name := range names {
 		factory := factories[name]
+		if factory == nil {
+			return nil, fmt.Errorf("failed to create service %s: factory is nil", name)
+		}
 		svc, err := factory()
 		if err != nil {
 			return nil, fmt.Errorf("failed to create service %s: %w", name, err)
@@ -99,14 +99,15 @@ func (r *Runtime) ServiceName() string {
 
 // ServiceStartup is called by the GUI runtime at application startup.
 // This is where the Core's startup lifecycle is initiated.
-func (r *Runtime) ServiceStartup(ctx context.Context, options any) {
-	_ = r.Core.ServiceStartup(ctx, options)
+func (r *Runtime) ServiceStartup(ctx context.Context, options any) error {
+	return r.Core.ServiceStartup(ctx, options)
 }
 
 // ServiceShutdown is called by the GUI runtime at application shutdown.
 // This is where the Core's shutdown lifecycle is initiated.
-func (r *Runtime) ServiceShutdown(ctx context.Context) {
+func (r *Runtime) ServiceShutdown(ctx context.Context) error {
 	if r.Core != nil {
-		_ = r.Core.ServiceShutdown(ctx)
+		return r.Core.ServiceShutdown(ctx)
 	}
+	return nil
 }
diff --git a/pkg/core/runtime_pkg_test.go b/pkg/core/runtime_pkg_test.go
index 175b569..bc9b388 100644
--- a/pkg/core/runtime_pkg_test.go
+++ b/pkg/core/runtime_pkg_test.go
@@ -88,9 +88,9 @@ func TestNewWithFactories_Ugly(t *testing.T) {
 	factories := map[string]ServiceFactory{
 		"test": nil,
 	}
-	assert.Panics(t, func() {
-		_, _ = NewWithFactories(nil, factories)
-	})
+	_, err := NewWithFactories(nil, factories)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "factory is nil")
 }
 
 func TestRuntime_Lifecycle_Good(t *testing.T) {
diff --git a/pkg/core/service_manager.go b/pkg/core/service_manager.go
index 9c4b0bd..0105cf7 100644
--- a/pkg/core/service_manager.go
+++ b/pkg/core/service_manager.go
@@ -3,6 +3,7 @@ package core
 import (
 	"errors"
 	"fmt"
+	"slices"
 	"sync"
 )
 
@@ -81,7 +82,7 @@ func (m *serviceManager) applyLock() {
 // getStartables returns a snapshot copy of the startables slice.
 func (m *serviceManager) getStartables() []Startable {
 	m.mu.RLock()
-	out := append([]Startable(nil), m.startables...)
+	out := slices.Clone(m.startables)
 	m.mu.RUnlock()
 	return out
 }
@@ -89,7 +90,7 @@ func (m *serviceManager) getStartables() []Startable {
 // getStoppables returns a snapshot copy of the stoppables slice.
 func (m *serviceManager) getStoppables() []Stoppable {
 	m.mu.RLock()
-	out := append([]Stoppable(nil), m.stoppables...)
+	out := slices.Clone(m.stoppables)
 	m.mu.RUnlock()
 	return out
 }