feat: close STREAMING.md production readiness gaps

- Added run ID + unique segment naming (r-{ISOTIME}/seg-{seq}.m4s)
- Added fsnotify watcher for real-time R2 segment upload (~7s)
- Added atomic manifest publication (temp key → CopyObject)
- Fixed manifest Cache-Control: public, max-age=1, s-maxage=2, must-revalidate
- Added hls.js error recovery: bounded retries (5x), exponential backoff, reconnecting UI
- Enriched /health endpoint: run_id, active_item, last_segment_seq, last_r2_pub, consecutive_failures, unhealthy detection
- Updated tests: HealthHandler (new fields + unhealthy), player error recovery test
- Updated TODO.md, BACKLOG.md, DONE.md, MEMORY.md

backend/playout/src/playlist_test.go

@@ -241,11 +241,15 @@ func TestHealthHandler(t *testing.T) {
 	// Save and restore globals
 	prevMode := playoutMode
 	prevCount := restartCount
+	prevRunID := runID
 	playoutMode = "live"
 	restartCount = 3
+	runID = "r-20260810T120000Z"
+	lastR2PubTime = time.Now()
 	defer func() {
 		playoutMode = prevMode
 		restartCount = prevCount
+		runID = prevRunID
 	}()
 
 	req := httptest.NewRequest("GET", "/health", nil)
@@ -257,21 +261,30 @@ func TestHealthHandler(t *testing.T) {
 	}
 
 	body := w.Body.String()
-	if !strings.Contains(body, `"healthy"`) {
-		t.Errorf("body missing healthy: %s", body)
-	}
-	if !strings.Contains(body, `"playout"`) {
-		t.Errorf("body missing service: %s", body)
-	}
-	if !strings.Contains(body, `"restarts":3`) {
-		t.Errorf("body missing restarts: %s", body)
+	for _, want := range []string{
+		`"status":"healthy"`,
+		`"service":"playout"`,
+		`"mode":"live"`,
+		`"restarts":3`,
+		`"run_id":"r-20260810T120000Z"`,
+		`"last_segment_seq"`,
+		`"consecutive_failures"`,
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("body missing %q: %s", want, body)
+		}
 	}
 }
 
 func TestHealthHandler_Degraded(t *testing.T) {
 	prevMode := playoutMode
+	prevR2Pub := lastR2PubTime
 	playoutMode = "slate"
-	defer func() { playoutMode = prevMode }()
+	lastR2PubTime = time.Now() // fresh R2 pub = not unhealthy
+	defer func() {
+		playoutMode = prevMode
+		lastR2PubTime = prevR2Pub
+	}()
 
 	req := httptest.NewRequest("GET", "/health", nil)
 	w := httptest.NewRecorder()
@@ -286,6 +299,26 @@ func TestHealthHandler_Degraded(t *testing.T) {
 	}
 }
 
+func TestHealthHandler_Unhealthy(t *testing.T) {
+	prevMode := playoutMode
+	prevR2Pub := lastR2PubTime
+	playoutMode = "live"
+	lastR2PubTime = time.Now().Add(-30 * time.Second) // stale R2 = unhealthy
+	defer func() {
+		playoutMode = prevMode
+		lastR2PubTime = prevR2Pub
+	}()
+
+	req := httptest.NewRequest("GET", "/health", nil)
+	w := httptest.NewRecorder()
+	HealthHandler(w, req)
+
+	body := w.Body.String()
+	if !strings.Contains(body, `"unhealthy"`) {
+		t.Errorf("body missing unhealthy (stale R2 pub should trigger unhealthy): %s", body)
+	}
+}
+
 func TestShouldEscalateToSlate(t *testing.T) {
 	// Save globals
 	prevCount := restartCount