diff --git a/lib/services/sync/sync_models.dart b/lib/services/sync/sync_models.dart
index 0c9d13f..f988bcd 100644
--- a/lib/services/sync/sync_models.dart
+++ b/lib/services/sync/sync_models.dart
@@ -1,16 +1,6 @@
 import 'package:flutter/foundation.dart';
 
-/// Strongly typed synchronization statuses with documented lifecycle transitions:
-///
-/// [localOnly] -> Initial state of historical or un-queued local rides.
-/// [queued] -> Placed in the outbox queue, ready for processing.
-/// [waitingForNetwork] -> Temporarily blocked due to absence of internet connectivity.
-/// [uploading] -> Actively transferring payload to the remote provider.
-/// [synced] -> Successfully confirmed and uploaded to the remote provider.
-/// [failed] -> Permanent failure or maximum retries exceeded.
-/// [retryWait] -> Temporary failure waiting for exponential backoff window.
-/// [authRequired] -> Provider requires authentication credentials before proceeding.
-/// [cancelled] -> Explicitly cancelled by user or invalidated by session.
+/// Persisted synchronization lifecycle.
 enum SyncStatus {
   localOnly,
   queued,
@@ -27,10 +17,11 @@ enum SyncStatus {
   bool get isInProgress => this == uploading;
 }
 
-/// Immutable outbox synchronization item referencing an authoritative local ride.
-/// Never stores raw sub-second telemetry points internally.
+/// Immutable outbox item. Raw telemetry is never stored here.
 @immutable
 class SyncItem {
+  static const int schemaVersion = 2;
+
   final int localRideId;
   final String providerId;
   final SyncStatus status;
@@ -57,19 +48,16 @@ class SyncItem {
     this.bundleLocalPath,
   });
 
-  /// Deterministic composite idempotency key preventing duplicate queue entries
-  String get key => '${localRideId}_$providerId';
+  /// Stable logical identity for one ride/provider destination.
+  String get key => '$providerId:$localRideId';
+
+  /// Stable idempotency identity shared by retries and app restarts.
+  String get idempotencyKey => key;
 
-  /// Whether this item is eligible for execution at the provided [now] timestamp
   bool isEligibleForAttempt(DateTime now) {
-    if (status == SyncStatus.synced || status == SyncStatus.failed || status == SyncStatus.cancelled) {
-      return false;
-    }
-    if (status == SyncStatus.uploading) {
-      return false;
-    }
+    if (status.isTerminal || status == SyncStatus.uploading) return false;
     if (status == SyncStatus.retryWait && nextRetryAt != null) {
-      return now.isAfter(nextRetryAt!) || now.isAtSameMomentAs(nextRetryAt!);
+      return !now.isBefore(nextRetryAt!);
     }
     return true;
   }
@@ -88,6 +76,8 @@ class SyncItem {
     String? bundleLocalPath,
     bool clearLastError = false,
     bool clearNextRetry = false,
+    bool clearRemoteId = false,
+    bool clearUploadedAt = false,
   }) {
     return SyncItem(
       localRideId: localRideId ?? this.localRideId,
@@ -97,14 +87,15 @@ class SyncItem {
       attemptCount: attemptCount ?? this.attemptCount,
       lastAttemptAt: lastAttemptAt ?? this.lastAttemptAt,
       nextRetryAt: clearNextRetry ? null : (nextRetryAt ?? this.nextRetryAt),
-      uploadedAt: uploadedAt ?? this.uploadedAt,
-      remoteId: remoteId ?? this.remoteId,
+      uploadedAt: clearUploadedAt ? null : (uploadedAt ?? this.uploadedAt),
+      remoteId: clearRemoteId ? null : (remoteId ?? this.remoteId),
       lastError: clearLastError ? null : (lastError ?? this.lastError),
       bundleLocalPath: bundleLocalPath ?? this.bundleLocalPath,
     );
   }
 
   Map<String, dynamic> toJson() => {
+        'schemaVersion': schemaVersion,
         'localRideId': localRideId,
         'providerId': providerId,
         'status': status.name,
@@ -118,34 +109,50 @@ class SyncItem {
         'bundleLocalPath': bundleLocalPath,
       };
 
-  factory SyncItem.fromJson(Map<String, dynamic> json) => SyncItem(
-        localRideId: json['localRideId'] as int,
-        providerId: json['providerId'] as String,
-        status: SyncStatus.values.firstWhere(
-          (e) => e.name == json['status'],
-          orElse: () => SyncStatus.queued,
-        ),
-        createdAt: DateTime.parse(json['createdAt'] as String),
-        attemptCount: json['attemptCount'] as int? ?? 0,
-        lastAttemptAt: json['lastAttemptAt'] != null
-            ? DateTime.tryParse(json['lastAttemptAt'] as String)
-            : null,
-        nextRetryAt: json['nextRetryAt'] != null
-            ? DateTime.tryParse(json['nextRetryAt'] as String)
-            : null,
-        uploadedAt: json['uploadedAt'] != null
-            ? DateTime.tryParse(json['uploadedAt'] as String)
-            : null,
-        remoteId: json['remoteId'] as String?,
-        lastError: json['lastError'] as String?,
-        bundleLocalPath: json['bundleLocalPath'] as String?,
-      );
+  factory SyncItem.fromJson(Map<String, dynamic> json) {
+    final localRideId = (json['localRideId'] as num?)?.toInt();
+    final providerId = json['providerId'];
+    final createdAtRaw = json['createdAt'];
+    if (localRideId == null || localRideId <= 0 || providerId is! String || providerId.trim().isEmpty || createdAtRaw is! String) {
+      throw const FormatException('Invalid sync item identity or createdAt');
+    }
+
+    final statusName = json['status'] as String?;
+    final status = SyncStatus.values.firstWhere(
+      (e) => e.name == statusName,
+      orElse: () => SyncStatus.queued,
+    );
+    final createdAt = DateTime.tryParse(createdAtRaw);
+    if (createdAt == null) throw const FormatException('Invalid sync item createdAt');
+
+    DateTime? parseDate(String key) {
+      final value = json[key];
+      if (value == null) return null;
+      if (value is! String) throw FormatException('Invalid $key');
+      return DateTime.tryParse(value);
+    }
+
+    final attempts = (json['attemptCount'] as num?)?.toInt() ?? 0;
+    if (attempts < 0) throw const FormatException('Negative attemptCount');
+
+    return SyncItem(
+      localRideId: localRideId,
+      providerId: providerId.trim(),
+      status: status,
+      createdAt: createdAt,
+      attemptCount: attempts,
+      lastAttemptAt: parseDate('lastAttemptAt'),
+      nextRetryAt: parseDate('nextRetryAt'),
+      uploadedAt: parseDate('uploadedAt'),
+      remoteId: json['remoteId'] as String?,
+      lastError: json['lastError'] as String?,
+      bundleLocalPath: json['bundleLocalPath'] as String?,
+    );
+  }
 
   @override
-  bool operator ==(Object other) =>
-      identical(this, other) ||
+  bool operator ==(Object other) => identical(this, other) ||
       other is SyncItem &&
-          runtimeType == other.runtimeType &&
           localRideId == other.localRideId &&
           providerId == other.providerId &&
           status == other.status &&
@@ -155,21 +162,12 @@ class SyncItem {
           lastError == other.lastError;
 
   @override
-  int get hashCode =>
-      localRideId.hashCode ^
-      providerId.hashCode ^
-      status.hashCode ^
-      attemptCount.hashCode ^
-      nextRetryAt.hashCode ^
-      remoteId.hashCode ^
-      lastError.hashCode;
+  int get hashCode => Object.hash(localRideId, providerId, status, attemptCount, nextRetryAt, remoteId, lastError);
 
   @override
-  String toString() =>
-      'SyncItem(ride: $localRideId, provider: $providerId, status: ${status.name}, attempts: $attemptCount, nextRetry: $nextRetryAt)';
+  String toString() => 'SyncItem(ride: $localRideId, provider: $providerId, status: ${status.name}, attempts: $attemptCount, nextRetry: $nextRetryAt)';
 }
 
-/// Result returned from a SyncProvider upload operation
 @immutable
 class SyncResult {
   final bool success;
@@ -188,56 +186,15 @@ class SyncResult {
     DateTime? timestamp,
   }) : timestamp = timestamp ?? DateTime.now();
 
-  SyncResult.success({
-    required String remoteId,
-    DateTime? timestamp,
-  }) : this(
-          success: true,
-          remoteId: remoteId,
-          isRetryable: false,
-          requiresAuth: false,
-          timestamp: timestamp,
-        );
-
-  SyncResult.temporaryFailure(
-    String message, {
-    DateTime? timestamp,
-  }) : this(
-          success: false,
-          errorMessage: message,
-          isRetryable: true,
-          requiresAuth: false,
-          timestamp: timestamp,
-        );
-
-  SyncResult.permanentFailure(
-    String message, {
-    DateTime? timestamp,
-  }) : this(
-          success: false,
-          errorMessage: message,
-          isRetryable: false,
-          requiresAuth: false,
-          timestamp: timestamp,
-        );
-
-  SyncResult.authRequired({
-    String message = 'Authentication credentials required for sync',
-    DateTime? timestamp,
-  }) : this(
-          success: false,
-          errorMessage: message,
-          isRetryable: true,
-          requiresAuth: true,
-          timestamp: timestamp,
-        );
+  SyncResult.success({required String remoteId, DateTime? timestamp}) : this(success: true, remoteId: remoteId, isRetryable: false, requiresAuth: false, timestamp: timestamp);
+  SyncResult.temporaryFailure(String message, {DateTime? timestamp}) : this(success: false, errorMessage: message, isRetryable: true, timestamp: timestamp);
+  SyncResult.permanentFailure(String message, {DateTime? timestamp}) : this(success: false, errorMessage: message, isRetryable: false, timestamp: timestamp);
+  SyncResult.authRequired({String message = 'Authentication credentials required for sync', DateTime? timestamp}) : this(success: false, errorMessage: message, isRetryable: true, requiresAuth: true, timestamp: timestamp);
 
   @override
-  String toString() =>
-      'SyncResult(success: $success, remoteId: $remoteId, error: $errorMessage, retryable: $isRetryable, auth: $requiresAuth)';
+  String toString() => 'SyncResult(success: $success, remoteId: $remoteId, error: $errorMessage, retryable: $isRetryable, auth: $requiresAuth)';
 }
 
-/// Aggregated synchronization state exposed to Riverpod UI
 @immutable
 class SyncManagerState {
   final bool isProcessing;
@@ -257,25 +214,4 @@ class SyncManagerState {
     this.lastError,
     this.activeProviderId = 'none',
   });
-
-  SyncManagerState copyWith({
-    bool? isProcessing,
-    int? pendingCount,
-    int? syncedCount,
-    int? failedCount,
-    DateTime? lastSuccessfulSync,
-    String? lastError,
-    String? activeProviderId,
-    bool clearLastError = false,
-  }) {
-    return SyncManagerState(
-      isProcessing: isProcessing ?? this.isProcessing,
-      pendingCount: pendingCount ?? this.pendingCount,
-      syncedCount: syncedCount ?? this.syncedCount,
-      failedCount: failedCount ?? this.failedCount,
-      lastSuccessfulSync: lastSuccessfulSync ?? this.lastSuccessfulSync,
-      lastError: clearLastError ? null : (lastError ?? this.lastError),
-      activeProviderId: activeProviderId ?? this.activeProviderId,
-    );
-  }
 }