diff --git a/docs/API.md b/docs/API.md
index 57301bb..c8807d4 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -15,6 +15,8 @@ Health check.
 {"ok": true}
 ```
 
+`engine.state` spiegelt jetzt die Runtime-State-Maschine wider (idle, arming, prebuffering, running, degraded, muted, faulted, stopping) und bietet eine erste beobachtbare Basis für Fault-Transitions.
+
 ---
 
 ### `GET /status`
@@ -73,6 +75,8 @@ Live engine and driver telemetry. Only populated when TX is active.
 }
 ```
 
+`engine.state` spiegelt jetzt die Runtime-State-Maschine wider (idle, arming, prebuffering, running, degraded, muted, faulted, stopping) und bietet eine erste beobachtbare Basis für Fault-Transitions.
+
 ---
 
 ### `GET /config`
diff --git a/docs/pro-runtime-hardening-workboard.md b/docs/pro-runtime-hardening-workboard.md
index b825bb4..e993968 100644
--- a/docs/pro-runtime-hardening-workboard.md
+++ b/docs/pro-runtime-hardening-workboard.md
@@ -266,11 +266,14 @@ Generator/Upsampler und Hardwarewriter werden als getrennte Stufen mit kleinem,
 
 # WS-02 — Explizite Runtime-State-Maschine und Fault-Handling
 **Priorität:** P0  
-**Gesamtstatus:** TODO
+**Gesamtstatus:** IN PROGRESS
 
 ## Ziel
 Einführen eines klaren Betriebsmodells mit Fault-, Recovery- und Muted-Zuständen.
 
+## Fortschritt
+- EngineStats liefert das Runtime-State-Feld (`idle`, `arming`, `prebuffering`, `running`) und schafft eine beobachtbare Baseline für die nächste Fault-Maschine.
+
 ## Zielzustände laut Konzept
 - `idle`
 - `arming`
diff --git a/internal/app/engine.go b/internal/app/engine.go
index a4836e9..2736766 100644
--- a/internal/app/engine.go
+++ b/internal/app/engine.go
@@ -38,6 +38,19 @@ func (s EngineState) String() string {
 	}
 }
 
+type RuntimeState string
+
+const (
+	RuntimeStateIdle         RuntimeState = "idle"
+	RuntimeStateArming       RuntimeState = "arming"
+	RuntimeStatePrebuffering RuntimeState = "prebuffering"
+	RuntimeStateRunning      RuntimeState = "running"
+	RuntimeStateDegraded     RuntimeState = "degraded"
+	RuntimeStateMuted        RuntimeState = "muted"
+	RuntimeStateFaulted      RuntimeState = "faulted"
+	RuntimeStateStopping     RuntimeState = "stopping"
+)
+
 func updateMaxDuration(dst *atomic.Uint64, d time.Duration) {
 	v := uint64(d)
 	for {
@@ -96,11 +109,12 @@ type Engine struct {
 	deviceRate    float64
 	frameQueue    *output.FrameQueue
 
-	mu        sync.Mutex
-	state     EngineState
-	cancel    context.CancelFunc
-	startedAt time.Time
-	wg        sync.WaitGroup
+	mu           sync.Mutex
+	state        EngineState
+	cancel       context.CancelFunc
+	startedAt    time.Time
+	wg           sync.WaitGroup
+	runtimeState atomic.Value
 
 	chunksProduced    atomic.Uint64
 	totalSamples      atomic.Uint64
@@ -177,7 +191,7 @@ func NewEngine(cfg cfgpkg.Config, driver platform.SoapyDriver) *Engine {
 		log.Printf("engine: same-rate mode — DSP@%dHz", cfg.FM.CompositeRateHz)
 	}
 
-	return &Engine{
+	engine := &Engine{
 		cfg:           cfg,
 		driver:        driver,
 		generator:     offpkg.NewGenerator(cfg),
@@ -187,6 +201,8 @@ func NewEngine(cfg cfgpkg.Config, driver platform.SoapyDriver) *Engine {
 		state:         EngineIdle,
 		frameQueue:    output.NewFrameQueue(cfg.Runtime.FrameQueueCapacity),
 	}
+	engine.setRuntimeState(RuntimeStateIdle)
+	return engine
 }
 
 func (e *Engine) SetChunkDuration(d time.Duration) {
@@ -306,6 +322,7 @@ func (e *Engine) Start(ctx context.Context) error {
 	runCtx, cancel := context.WithCancel(ctx)
 	e.cancel = cancel
 	e.state = EngineRunning
+	e.setRuntimeState(RuntimeStateArming)
 	e.startedAt = time.Now()
 	e.wg.Add(1)
 	e.mu.Unlock()
@@ -321,6 +338,7 @@ func (e *Engine) Stop(ctx context.Context) error {
 		return nil
 	}
 	e.state = EngineStopping
+	e.setRuntimeState(RuntimeStateStopping)
 	e.cancel()
 	e.mu.Unlock()
 
@@ -336,6 +354,7 @@ func (e *Engine) Stop(ctx context.Context) error {
 
 	e.mu.Lock()
 	e.state = EngineIdle
+	e.setRuntimeState(RuntimeStateIdle)
 	e.mu.Unlock()
 	return nil
 }
@@ -359,7 +378,7 @@ func (e *Engine) Stats() EngineStats {
 	hasRecentLateBuffers := lateAlertAt > 0 && now.Sub(time.Unix(0, int64(lateAlertAt))) <= lateBufferIndicatorWindow
 	ri := runtimeIndicator(queue.Health, hasRecentLateBuffers)
 	return EngineStats{
-		State:            state.String(),
+		State:            string(e.currentRuntimeState()),
 		ChunksProduced:   e.chunksProduced.Load(),
 		TotalSamples:     e.totalSamples.Load(),
 		Underruns:        e.underruns.Load(),
@@ -401,6 +420,7 @@ func runtimeAlert(queueHealth output.QueueHealth, recentLateBuffers bool) string
 }
 
 func (e *Engine) run(ctx context.Context) {
+	e.setRuntimeState(RuntimeStateRunning)
 	e.wg.Add(1)
 	go e.writerLoop(ctx)
 	defer e.wg.Done()
@@ -530,3 +550,16 @@ func cloneFrame(src *output.CompositeFrame) *output.CompositeFrame {
 		Sequence:     src.Sequence,
 	}
 }
+
+func (e *Engine) setRuntimeState(state RuntimeState) {
+	e.runtimeState.Store(state)
+}
+
+func (e *Engine) currentRuntimeState() RuntimeState {
+	if v := e.runtimeState.Load(); v != nil {
+		if rs, ok := v.(RuntimeState); ok {
+			return rs
+		}
+	}
+	return RuntimeStateIdle
+}
diff --git a/internal/app/runtime_state_test.go b/internal/app/runtime_state_test.go
new file mode 100644
index 0000000..9ef04be
--- /dev/null
+++ b/internal/app/runtime_state_test.go
@@ -0,0 +1,26 @@
+package app
+
+import (
+	"testing"
+
+	cfgpkg "github.com/jan/fm-rds-tx/internal/config"
+	"github.com/jan/fm-rds-tx/internal/platform"
+)
+
+func TestEngineRuntimeStateReporting(t *testing.T) {
+	e := NewEngine(cfgpkg.Default(), platform.NewSimulatedDriver(nil))
+
+	if got := e.Stats().State; got != string(RuntimeStateIdle) {
+		t.Fatalf("expected initial state idle, got %s", got)
+	}
+
+	e.setRuntimeState(RuntimeStatePrebuffering)
+	if got := e.Stats().State; got != string(RuntimeStatePrebuffering) {
+		t.Fatalf("expected prebuffering, got %s", got)
+	}
+
+	e.setRuntimeState(RuntimeStateRunning)
+	if got := e.currentRuntimeState(); got != RuntimeStateRunning {
+		t.Fatalf("currentRuntimeState mismatch: %s", got)
+	}
+}