fix(streaming): refactor to not force session id

lib/core/services/api_service.dart

@@ -1170,9 +1170,7 @@ class ApiService {
         data,
         debugLabel: 'parse_file_search',
       );
-      return normalized
-          .map(FileInfo.fromJson)
-          .toList(growable: false);
+      return normalized.map(FileInfo.fromJson).toList(growable: false);
     }
     return const [];
   }
@@ -1186,9 +1184,7 @@ class ApiService {
         data,
         debugLabel: 'parse_file_all',
       );
-      return normalized
-          .map(FileInfo.fromJson)
-          .toList(growable: false);
+      return normalized.map(FileInfo.fromJson).toList(growable: false);
     }
     return const [];
   }
@@ -1599,10 +1595,7 @@ class ApiService {
     if (data is Map<String, dynamic>) {
       final voices = data['voices'];
       if (voices is List) {
-        return _normalizeList(
-          voices,
-          debugLabel: 'parse_voice_list',
-        );
+        return _normalizeList(voices, debugLabel: 'parse_voice_list');
       }
     }
     if (data is List) {
@@ -1705,10 +1698,7 @@ class ApiService {
     final response = await _dio.get('/api/v1/images/models');
     final data = response.data;
     if (data is List) {
-      return _normalizeList(
-        data,
-        debugLabel: 'parse_image_models',
-      );
+      return _normalizeList(data, debugLabel: 'parse_image_models');
     }
     return [];
   }
@@ -2406,7 +2396,7 @@ class ApiService {
   ({
     Stream<String> stream,
     String messageId,
-    String sessionId,
+    String? sessionId,
     String? socketSessionId,
     bool isBackgroundFlow,
   })
@@ -2432,10 +2422,9 @@ class ApiService {
         (responseMessageId != null && responseMessageId.isNotEmpty)
         ? responseMessageId
         : const Uuid().v4();
-    final sessionId =
-        (sessionIdOverride != null && sessionIdOverride.isNotEmpty)
-        ? sessionIdOverride
-        : const Uuid().v4().substring(0, 20);
+    final bool hasSocketBinding =
+        sessionIdOverride != null && sessionIdOverride.isNotEmpty;
+    final String? sessionId = hasSocketBinding ? sessionIdOverride : null;
 
     // NOTE: Previously used to branch for Gemini-specific handling; not needed now.
 
@@ -2586,14 +2575,20 @@ class ApiService {
     );
 
     // Attach identifiers to trigger background task processing on the server
-    data['session_id'] = sessionId;
+    if (sessionId != null) {
+      data['session_id'] = sessionId;
+    }
     data['id'] = messageId;
     if (conversationId != null) {
       data['chat_id'] = conversationId;
     }
 
-    // Attach background_tasks if provided
-    if (backgroundTasks != null && backgroundTasks.isNotEmpty) {
+    final bool includeBackgroundTasks =
+        backgroundTasks != null &&
+        backgroundTasks.isNotEmpty &&
+        sessionId != null;
+
+    if (includeBackgroundTasks) {
       data['background_tasks'] = backgroundTasks;
     }
 
@@ -2717,7 +2712,7 @@ class ApiService {
       messageId: messageId,
       sessionId: sessionId,
       socketSessionId: socketSessionId,
-      isBackgroundFlow: true,
+      isBackgroundFlow: includeBackgroundTasks,
     );
   }
 
@@ -3123,10 +3118,7 @@ class ApiService {
 
       final data = response.data;
       if (data is List) {
-        return _normalizeList(
-          data,
-          debugLabel: 'parse_message_search',
-        );
+        return _normalizeList(data, debugLabel: 'parse_message_search');
       }
       if (data is Map<String, dynamic>) {
         final list = (data['items'] ?? data['results'] ?? data['messages']);

lib/core/services/streaming_helper.dart

@@ -135,7 +135,7 @@ ActiveSocketStream attachUnifiedChunkedStreaming({
   required String assistantMessageId,
   required String modelId,
   required Map<String, dynamic> modelItem,
-  required String sessionId,
+  required String? sessionId,
   required String? activeConversationId,
   required ApiService api,
   required SocketService? socketService,
@@ -238,6 +238,7 @@ ActiveSocketStream attachUnifiedChunkedStreaming({
       'conversationId': activeConversationId,
       'messageId': assistantMessageId,
       'modelId': modelId,
+      if (sessionId != null) 'sessionId': sessionId,
     },
   );
   api.registerPersistentStreamForMessage(assistantMessageId, streamId);