feat: persist and restore demo stream configuration

- Added persistence of demo stream type and count to maintain user preferences across sessions
- Enhanced demo stream selection to automatically restore previously selected configuration
- Added fallback logic to match saved sampling rate and stream count when exact demo type not found
- Updated secondary stream initialization to track total demo streams across primary/secondary configs
- Modified settings storage to include demo_stream_type and demo

src/auracast/server/multicast_frontend.py

@@ -170,11 +170,29 @@ if audio_mode == "Demo":
         "6 × 16kHz": {"quality": "Fair (16kHz)", "streams": 6},
     }
     demo_options = list(demo_stream_map.keys())
-    default_demo = demo_options[0]
+    default_index = 0
+    saved_type = saved_settings.get('demo_stream_type')
+    if isinstance(saved_type, str) and saved_type in demo_options:
+        default_index = demo_options.index(saved_type)
+    else:
+        saved_rate = saved_settings.get('auracast_sampling_rate_hz')
+        saved_total = saved_settings.get('demo_total_streams')
+        if saved_total is None and saved_settings.get('audio_mode') == 'Demo':
+            saved_total = len(saved_settings.get('channel_names') or [])
+        try:
+            if saved_rate and saved_total:
+                for i, label in enumerate(demo_options):
+                    cfg = demo_stream_map[label]
+                    rate_for_label = QUALITY_MAP[cfg['quality']]['rate']
+                    if cfg['streams'] == int(saved_total) and int(saved_rate) == rate_for_label:
+                        default_index = i
+                        break
+        except Exception:
+            default_index = 0
     demo_selected = st.selectbox(
         "Demo Stream Type",
         demo_options,
-        index=0,
+        index=default_index,
         help="Select the demo stream configuration."
     )
     # Stream password and flags (same as USB/AES67)

src/auracast/server/multicast_server.py

@@ -219,6 +219,14 @@ class StreamerWorker: # TODO: is wraping in this Worker stricly nececcarry ?
             auto_started = True
 
         # Return proposed settings to persist on API side
+        demo_count = sum(1 for big in conf.bigs if isinstance(big.audio_source, str) and big.audio_source.startswith('file:'))
+        demo_rate = int(conf.auracast_sampling_rate_hz or 0)
+        demo_type = None
+        if demo_count > 0 and demo_rate > 0:
+            if demo_rate in (48000, 24000, 16000):
+                demo_type = f"{demo_count} × {demo_rate//1000}kHz"
+            else:
+                demo_type = f"{demo_count} × {demo_rate}Hz"
         return {
             'channel_names': [big.name for big in conf.bigs],
             'languages': [big.language for big in conf.bigs],
@@ -233,6 +241,8 @@ class StreamerWorker: # TODO: is wraping in this Worker stricly nececcarry ?
             'immediate_rendering': getattr(conf, 'immediate_rendering', False),
             'assisted_listening_stream': getattr(conf, 'assisted_listening_stream', False),
             'stream_password': (conf.bigs[0].code if conf.bigs and getattr(conf.bigs[0], 'code', None) else None),
+            'demo_total_streams': demo_count,
+            'demo_stream_type': demo_type,
             'is_streaming': auto_started,
         }
 
@@ -345,6 +355,24 @@ async def initialize2(conf: auracast_config.AuracastConfigGroup):
     try:
         log.info('Initializing multicaster2 with config:\n %s', conf.model_dump_json(indent=2))
         await streamer.call(streamer._w_init_secondary, conf)
+        try:
+            is_demo = any(isinstance(big.audio_source, str) and big.audio_source.startswith('file:') for big in conf.bigs)
+            if is_demo:
+                settings = load_stream_settings() or {}
+                primary_count = int(settings.get('demo_total_streams') or len(settings.get('channel_names') or []))
+                secondary_count = len(conf.bigs or [])
+                total = primary_count + secondary_count
+                settings['demo_total_streams'] = total
+                demo_rate = int(conf.auracast_sampling_rate_hz or 0)
+                if demo_rate > 0:
+                    if demo_rate in (48000, 24000, 16000):
+                        settings['demo_stream_type'] = f"{total} × {demo_rate//1000}kHz"
+                    else:
+                        settings['demo_stream_type'] = f"{total} × {demo_rate}Hz"
+                settings['timestamp'] = datetime.utcnow().isoformat()
+                save_stream_settings(settings)
+        except Exception:
+            log.warning("Failed to persist demo_total_streams in /init2", exc_info=True)
     except Exception as e:
         log.error("Exception in /init2: %s", traceback.format_exc())
         raise HTTPException(status_code=500, detail=str(e))