feat: task based send flow

lib/shared/services/tasks/outbound_task.dart

@@ -0,0 +1,70 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'outbound_task.freezed.dart';
+part 'outbound_task.g.dart';
+
+enum TaskStatus {
+  queued,
+  running,
+  succeeded,
+  failed,
+  cancelled,
+}
+
+@freezed
+abstract class OutboundTask with _$OutboundTask {
+  const OutboundTask._();
+
+  const factory OutboundTask.sendTextMessage({
+    required String id,
+    String? conversationId,
+    required String text,
+    @Default(<String>[]) List<String> attachments,
+    @Default(<String>[]) List<String> toolIds,
+    @Default(TaskStatus.queued) TaskStatus status,
+    @Default(0) int attempt,
+    String? idempotencyKey,
+    DateTime? enqueuedAt,
+    DateTime? startedAt,
+    DateTime? completedAt,
+    String? error,
+  }) = SendTextMessageTask;
+
+  const factory OutboundTask.uploadMedia({
+    required String id,
+    String? conversationId,
+    required String filePath,
+    required String fileName,
+    int? fileSize,
+    String? mimeType,
+    String? checksum,
+    @Default(TaskStatus.queued) TaskStatus status,
+    @Default(0) int attempt,
+    String? idempotencyKey,
+    DateTime? enqueuedAt,
+    DateTime? startedAt,
+    DateTime? completedAt,
+    String? error,
+  }) = UploadMediaTask;
+
+  const factory OutboundTask.executeToolCall({
+    required String id,
+    String? conversationId,
+    required String toolName,
+    @Default(<String, dynamic>{}) Map<String, dynamic> arguments,
+    @Default(TaskStatus.queued) TaskStatus status,
+    @Default(0) int attempt,
+    String? idempotencyKey,
+    DateTime? enqueuedAt,
+    DateTime? startedAt,
+    DateTime? completedAt,
+    String? error,
+  }) = ExecuteToolCallTask;
+
+  factory OutboundTask.fromJson(Map<String, dynamic> json) =>
+      _$OutboundTaskFromJson(json);
+
+  String get threadKey => (conversationId == null || conversationId!.isEmpty)
+      ? 'new'
+      : conversationId!;
+}