diff --git a/Archive.zip b/Archive.zip
deleted file mode 100644
index e760bfd..0000000
Binary files a/Archive.zip and /dev/null differ
diff --git a/README.md b/README.md
index 96d0197..715bc3f 100644
--- a/README.md
+++ b/README.md
@@ -34,9 +34,15 @@ If Gradle reports `Could not find org.asyncstorage.shared_storage:storage-androi
 
 1. While online, open **Events** and tap the cloud icon (or long-press an event) → **Enable Offline**.
 2. The app downloads active attendance sessions + participant rosters into local SQLite.
-3. Check in via search or QR without internet; items queue in an outbox.
-4. Tap **Sync** (or wait for reconnect) to flush via `POST .../check-ins/sync`.
-5. **Refresh Offline Data** updates the snapshot without clearing pending outbox rows.
+3. While Offline is on, search and QR check-ins always save locally (even with internet). They queue in an outbox.
+4. Every minute while online (app in the foreground), pending check-ins are **uploaded**. Reconnect and returning to the app also upload.
+5. Header **Sync** is two-way at that page’s scope:
+   - **Events** — all Offline-enabled events (upload pending + refresh all sheets)
+   - **Attendance sessions** — this event (upload pending + refresh all sheets)
+   - **Participants** — this attendance sheet only (upload pending + refresh this roster)
+6. **Refresh Offline Data** (long-press an event) is a recovery pull of the snapshot without clearing pending outbox rows.
+7. **Assign a Blank** (when enabled on the attendance session in the dashboard) scans a spare badge QR, lets staff edit name/email/phone, then saves — updating that participant and checking them in. It uses the same offline outbox as check-ins.
+8. **Undo** on the check-in success sheet reverses the last check-in. For a later mistake, swipe a checked-in row left to reveal **Uncheck-in**. Staff-only; last check-in only; same offline queue. Does not revert Assign a Blank profile.
 
 Native rebuild is required after installing `@op-engineering/op-sqlite` / NetInfo (`npm run android` / `npm run ios`).
 
diff --git a/package-lock.json b/package-lock.json
index 9e9ebc6..ba58e15 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,6 +17,7 @@
         "react": "19.2.3",
         "react-native": "0.85.3",
         "react-native-config": "^1.6.1",
+        "react-native-gesture-handler": "^2.28.0",
         "react-native-get-random-values": "^2.0.0",
         "react-native-safe-area-context": "^5.5.2",
         "react-native-screens": "^4.25.1",
@@ -2026,6 +2027,18 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@egjs/hammerjs": {
+      "version": "2.0.17",
+      "resolved": "https://registry.npmjs.org/@egjs/hammerjs/-/hammerjs-2.0.17.tgz",
+      "integrity": "sha512-XQsZgjm2EcVUiZQf11UBJQfmZeEmOW8DpI1gsFeln6w0ae0ii4dMQEQ0kjl6DspdWX1aGY1/loyXnP0JS06e/A==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/hammerjs": "^2.0.36"
+      },
+      "engines": {
+        "node": ">=0.8.0"
+      }
+    },
     "node_modules/@eslint-community/eslint-utils": {
       "version": "4.9.1",
       "resolved": "https://registry.npmjs.org/@eslint-community/eslint-utils/-/eslint-utils-4.9.1.tgz",
@@ -3621,6 +3634,12 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/hammerjs": {
+      "version": "2.0.46",
+      "resolved": "https://registry.npmjs.org/@types/hammerjs/-/hammerjs-2.0.46.tgz",
+      "integrity": "sha512-ynRvcq6wvqexJ9brDMS4BnBLzmr0e14d6ZJTEShTBWKymQiHwlAyGu0ZPEFI2Fh1U53F7tN9ufClWM5KvqkKOw==",
+      "license": "MIT"
+    },
     "node_modules/@types/istanbul-lib-coverage": {
       "version": "2.0.6",
       "resolved": "https://registry.npmjs.org/@types/istanbul-lib-coverage/-/istanbul-lib-coverage-2.0.6.tgz",
@@ -7121,6 +7140,21 @@
         "hermes-estree": "0.33.3"
       }
     },
+    "node_modules/hoist-non-react-statics": {
+      "version": "3.3.2",
+      "resolved": "https://registry.npmjs.org/hoist-non-react-statics/-/hoist-non-react-statics-3.3.2.tgz",
+      "integrity": "sha512-/gGivxi8JPKWNm/W0jSmzcMPpfpPLc3dY/6GxhX2hQ9iGj3aDfklV4ET7NjKpSinLpJ5vafa9iiGIEZg10SfBw==",
+      "license": "BSD-3-Clause",
+      "dependencies": {
+        "react-is": "^16.7.0"
+      }
+    },
+    "node_modules/hoist-non-react-statics/node_modules/react-is": {
+      "version": "16.13.1",
+      "resolved": "https://registry.npmjs.org/react-is/-/react-is-16.13.1.tgz",
+      "integrity": "sha512-24e6ynE2H+OKt4kqsOvNd8kBpV65zoxbA4BVsEOB3ARVWQki/DHzaUoC5KuON/BiccDaCCTZBuOcfZs70kR8bQ==",
+      "license": "MIT"
+    },
     "node_modules/html-escaper": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/html-escaper/-/html-escaper-2.0.2.tgz",
@@ -10465,6 +10499,21 @@
         }
       }
     },
+    "node_modules/react-native-gesture-handler": {
+      "version": "2.28.0",
+      "resolved": "https://registry.npmjs.org/react-native-gesture-handler/-/react-native-gesture-handler-2.28.0.tgz",
+      "integrity": "sha512-0msfJ1vRxXKVgTgvL+1ZOoYw3/0z1R+Ked0+udoJhyplC2jbVKIJ8Z1bzWdpQRCV3QcQ87Op0zJVE5DhKK2A0A==",
+      "license": "MIT",
+      "dependencies": {
+        "@egjs/hammerjs": "^2.0.17",
+        "hoist-non-react-statics": "^3.3.0",
+        "invariant": "^2.2.4"
+      },
+      "peerDependencies": {
+        "react": "*",
+        "react-native": "*"
+      }
+    },
     "node_modules/react-native-get-random-values": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/react-native-get-random-values/-/react-native-get-random-values-2.0.0.tgz",
diff --git a/src/api/attendances.ts b/src/api/attendances.ts
index 5099185..eb2330a 100644
--- a/src/api/attendances.ts
+++ b/src/api/attendances.ts
@@ -33,6 +33,30 @@ export const attendancesApi = {
     );
   },
 
+  undoCheckIn(eventId: string, attendanceId: string, participantId: string) {
+    return api.post<AttendanceCheckInResult>(
+      `/events/${eventId}/attendances/${attendanceId}/undo-check-in`,
+      { participantId },
+    );
+  },
+
+  assignBlank(
+    eventId: string,
+    attendanceId: string,
+    body: {
+      participantId: string;
+      firstName: string;
+      lastName?: string;
+      email?: string;
+      phone?: string;
+    },
+  ) {
+    return api.post<AttendanceCheckInResult>(
+      `/events/${eventId}/attendances/${attendanceId}/assign-blank`,
+      body,
+    );
+  },
+
   syncCheckIns(
     eventId: string,
     attendanceId: string,
diff --git a/src/api/types.ts b/src/api/types.ts
index 4b408d6..e7aaba5 100644
--- a/src/api/types.ts
+++ b/src/api/types.ts
@@ -43,6 +43,7 @@ export interface AttendanceRecord {
   status: 'active' | 'archived';
   settings?: {
     allowDuplicateCheckIn?: boolean;
+    allowAssignBlank?: boolean;
     publicLinkEnabled?: boolean;
   };
   uniqueParticipants?: number;
@@ -74,10 +75,19 @@ export interface AttendanceCheckInResult {
   alreadyCheckedIn: boolean;
 }
 
+export interface AssignBlankProfile {
+  firstName: string;
+  lastName?: string;
+  email?: string;
+  phone?: string;
+}
+
 export interface OfflineSyncOperation {
   clientOpId: string;
   participantId: string;
   checkedInAt: string;
+  profile?: AssignBlankProfile;
+  action?: 'check_in' | 'undo';
 }
 
 export interface OfflineSyncOpResult {
diff --git a/src/components/CheckInResultModal.tsx b/src/components/CheckInResultModal.tsx
index cc7a2b9..bf28e82 100644
--- a/src/components/CheckInResultModal.tsx
+++ b/src/components/CheckInResultModal.tsx
@@ -1,5 +1,5 @@
 import React from 'react';
-import { Modal, Pressable, StyleSheet, Text, View } from 'react-native';
+import { Alert, Modal, Pressable, StyleSheet, Text, View } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
 import type { AttendanceCheckInResult } from '../api/types';
 import { colors, radii, spacing, typography } from '../theme';
@@ -11,6 +11,8 @@ type Props = {
   error: string | null;
   pendingSync?: boolean;
   onClose: () => void;
+  onUndo?: () => void | Promise<void>;
+  undoLoading?: boolean;
 };
 
 const CHECKIN_GREEN = '#16A34A';
@@ -22,8 +24,25 @@ export function CheckInResultModal({
   error,
   pendingSync = false,
   onClose,
+  onUndo,
+  undoLoading = false,
 }: Props) {
   const insets = useSafeAreaInsets();
+  const showUndo = Boolean(result && onUndo && !error);
+
+  const confirmUndo = () => {
+    if (!result || !onUndo || undoLoading) return;
+    Alert.alert('Undo check-in', `Undo check-in for ${result.displayName}?`, [
+      { text: 'Cancel', style: 'cancel' },
+      {
+        text: 'Undo',
+        style: 'destructive',
+        onPress: () => {
+          void onUndo();
+        },
+      },
+    ]);
+  };
 
   return (
     <Modal visible={visible} transparent animationType="slide" onRequestClose={onClose}>
@@ -85,7 +104,23 @@ export function CheckInResultModal({
             </>
           ) : null}
 
-          <PrimaryButton title="Done" onPress={onClose} style={styles.doneBtn} />
+          <View style={styles.actions}>
+            {showUndo ? (
+              <Pressable
+                style={styles.undoBtn}
+                onPress={confirmUndo}
+                disabled={undoLoading}
+              >
+                <Text style={styles.undoText}>{undoLoading ? 'Undoing…' : 'Undo'}</Text>
+              </Pressable>
+            ) : null}
+            <PrimaryButton
+              title="Done"
+              onPress={onClose}
+              style={showUndo ? styles.doneBtnFlex : styles.doneBtn}
+              disabled={undoLoading}
+            />
+          </View>
         </Pressable>
       </Pressable>
     </Modal>
@@ -177,7 +212,30 @@ const styles = StyleSheet.create({
     color: PENDING_AMBER,
     fontWeight: '600',
   },
-  doneBtn: {
+  actions: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    gap: 12,
     marginTop: spacing.sm,
   },
+  undoBtn: {
+    height: 52,
+    paddingHorizontal: 18,
+    borderRadius: radii.md,
+    borderWidth: 1.5,
+    borderColor: colors.error,
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+  undoText: {
+    color: colors.error,
+    fontSize: 16,
+    fontWeight: '700',
+  },
+  doneBtn: {
+    flex: 1,
+  },
+  doneBtnFlex: {
+    flex: 1,
+  },
 });
diff --git a/src/components/SwipeRow.tsx b/src/components/SwipeRow.tsx
new file mode 100644
index 0000000..93f739d
--- /dev/null
+++ b/src/components/SwipeRow.tsx
@@ -0,0 +1,159 @@
+import React, { useEffect, useMemo, useRef, useState } from 'react';
+import {
+  Animated,
+  PanResponder,
+  Pressable,
+  StyleSheet,
+  Text,
+  View,
+  type LayoutChangeEvent,
+  type StyleProp,
+  type ViewStyle,
+} from 'react-native';
+import { colors, radii } from '../theme';
+
+const ACTION_WIDTH = 108;
+const OPEN_THRESHOLD = 40;
+
+type Props = {
+  enabled: boolean;
+  open: boolean;
+  onOpen: () => void;
+  onClose: () => void;
+  actionLabel: string;
+  onActionPress: () => void;
+  actionBusy?: boolean;
+  children: React.ReactNode;
+  style?: StyleProp<ViewStyle>;
+};
+
+export function SwipeRow({
+  enabled,
+  open,
+  onOpen,
+  onClose,
+  actionLabel,
+  onActionPress,
+  actionBusy = false,
+  children,
+  style,
+}: Props) {
+  const translateX = useRef(new Animated.Value(0)).current;
+  const startX = useRef(0);
+  const openRef = useRef(open);
+  openRef.current = open;
+  const [rowHeight, setRowHeight] = useState(0);
+
+  const snapTo = (toValue: number, after?: () => void) => {
+    Animated.spring(translateX, {
+      toValue,
+      useNativeDriver: true,
+      bounciness: 0,
+      speed: 20,
+    }).start(({ finished }) => {
+      if (finished) after?.();
+    });
+  };
+
+  useEffect(() => {
+    snapTo(open ? -ACTION_WIDTH : 0);
+  }, [open]);
+
+  const pan = useMemo(
+    () =>
+      PanResponder.create({
+        onMoveShouldSetPanResponder: (_e, g) => {
+          if (!enabled) return false;
+          return Math.abs(g.dx) > 8 && Math.abs(g.dx) > Math.abs(g.dy);
+        },
+        onMoveShouldSetPanResponderCapture: (_e, g) => {
+          if (!enabled) return false;
+          return Math.abs(g.dx) > 8 && Math.abs(g.dx) > Math.abs(g.dy);
+        },
+        onPanResponderTerminationRequest: () => false,
+        onPanResponderGrant: () => {
+          translateX.stopAnimation((value) => {
+            startX.current = value;
+          });
+        },
+        onPanResponderMove: (_e, g) => {
+          const next = Math.min(0, Math.max(-ACTION_WIDTH, startX.current + g.dx));
+          translateX.setValue(next);
+        },
+        onPanResponderRelease: (_e, g) => {
+          const projected = startX.current + g.dx;
+          const closingSwipe = openRef.current && (g.dx > OPEN_THRESHOLD || g.vx > 0.35);
+          const shouldOpen =
+            !closingSwipe && (projected < -OPEN_THRESHOLD || g.vx < -0.4);
+          if (shouldOpen) {
+            snapTo(-ACTION_WIDTH, onOpen);
+          } else {
+            snapTo(0, onClose);
+          }
+        },
+        onPanResponderTerminate: () => {
+          snapTo(openRef.current ? -ACTION_WIDTH : 0);
+        },
+      }),
+    [enabled, onClose, onOpen, translateX],
+  );
+
+  const onForegroundLayout = (e: LayoutChangeEvent) => {
+    const next = Math.round(e.nativeEvent.layout.height);
+    if (next > 0 && next !== rowHeight) setRowHeight(next);
+  };
+
+  if (!enabled) return <View style={style}>{children}</View>;
+
+  return (
+    <View style={style}>
+      <View style={styles.clip} {...pan.panHandlers}>
+        {rowHeight > 0 ? (
+          <View
+            style={[styles.actionWrap, { height: rowHeight }]}
+            pointerEvents={open ? 'auto' : 'none'}
+          >
+            <Pressable style={styles.action} onPress={actionBusy ? undefined : onActionPress}>
+              <Text style={styles.actionText}>{actionBusy ? '…' : actionLabel}</Text>
+            </Pressable>
+          </View>
+        ) : null}
+        <Animated.View
+          style={[styles.foreground, { transform: [{ translateX }] }]}
+          onLayout={onForegroundLayout}
+        >
+          {children}
+        </Animated.View>
+      </View>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  clip: {
+    overflow: 'hidden',
+    borderRadius: radii.xl,
+  },
+  actionWrap: {
+    position: 'absolute',
+    right: 0,
+    top: 0,
+    width: ACTION_WIDTH,
+  },
+  action: {
+    flex: 1,
+    backgroundColor: colors.error,
+    alignItems: 'center',
+    justifyContent: 'center',
+    paddingHorizontal: 10,
+  },
+  actionText: {
+    color: '#fff',
+    fontSize: 12,
+    fontWeight: '700',
+    textAlign: 'center',
+  },
+  foreground: {
+    backgroundColor: colors.card,
+  },
+});
diff --git a/src/components/ui/AppIcon.tsx b/src/components/ui/AppIcon.tsx
index b5076e5..992b168 100644
--- a/src/components/ui/AppIcon.tsx
+++ b/src/components/ui/AppIcon.tsx
@@ -23,6 +23,7 @@ export type AppIconName =
   | 'log-out-outline'
   | 'mail-outline'
   | 'people-outline'
+  | 'person-add-outline'
   | 'person-outline'
   | 'qr-code-outline'
   | 'refresh-outline'
diff --git a/src/navigation/RootNavigator.tsx b/src/navigation/RootNavigator.tsx
index c36bed4..23405e2 100644
--- a/src/navigation/RootNavigator.tsx
+++ b/src/navigation/RootNavigator.tsx
@@ -9,6 +9,7 @@ import { EventsScreen } from '../screens/EventsScreen';
 import { AttendanceSessionsScreen } from '../screens/AttendanceSessionsScreen';
 import { ParticipantsScreen } from '../screens/ParticipantsScreen';
 import { QrScannerScreen } from '../screens/QrScannerScreen';
+import { AssignBlankScreen } from '../screens/AssignBlankScreen';
 import type { RootStackParamList } from './types';
 import { colors } from '../theme';
 import { getAccessToken } from '../api/client';
@@ -89,6 +90,7 @@ export function RootNavigator() {
         <Stack.Screen name="Events" component={EventsScreen} />
         <Stack.Screen name="AttendanceSessions" component={AttendanceSessionsScreen} />
         <Stack.Screen name="Participants" component={ParticipantsScreen} />
+        <Stack.Screen name="AssignBlank" component={AssignBlankScreen} />
         <Stack.Screen
           name="QrScanner"
           component={QrScannerScreen}
diff --git a/src/navigation/types.ts b/src/navigation/types.ts
index 362aafb..62850a7 100644
--- a/src/navigation/types.ts
+++ b/src/navigation/types.ts
@@ -9,11 +9,26 @@ export type RootStackParamList = {
     attendanceId: string;
     attendanceName: string;
     allowDuplicate: boolean;
+    allowAssignBlank: boolean;
   };
   QrScanner: {
     eventId: string;
+    eventName: string;
     attendanceId: string;
     attendanceName: string;
     allowDuplicate: boolean;
+    allowAssignBlank?: boolean;
+    mode?: 'checkIn' | 'assignBlank';
+  };
+  AssignBlank: {
+    eventId: string;
+    eventName: string;
+    attendanceId: string;
+    attendanceName: string;
+    participantId: string;
+    firstName?: string;
+    lastName?: string;
+    email?: string;
+    phone?: string;
   };
 };
diff --git a/src/offline/OfflineContext.tsx b/src/offline/OfflineContext.tsx
index a525955..6a4b8e2 100644
--- a/src/offline/OfflineContext.tsx
+++ b/src/offline/OfflineContext.tsx
@@ -9,7 +9,7 @@ import React, {
 } from 'react';
 import { AppState, type AppStateStatus } from 'react-native';
 import { getDb } from './db';
-import { runSync, subscribeSyncEngine } from './syncEngine';
+import { runSync, subscribeSyncEngine, type SyncOpts, type SyncResult } from './syncEngine';
 import type { EventOfflineStatus } from './types';
 import { getEventOfflineStatus, listOfflineEventIds } from './repos';
 
@@ -20,11 +20,13 @@ type OfflineContextValue = {
   lastSyncError: string | null;
   statusByEvent: Record<string, EventOfflineStatus>;
   refreshStatuses: () => Promise<void>;
-  syncNow: (eventId?: string) => Promise<{ ok: boolean; flushed: number; error?: string }>;
+  syncNow: (opts?: SyncOpts) => Promise<SyncResult>;
 };
 
 const OfflineContext = createContext<OfflineContextValue | null>(null);
 
+const AUTO_SYNC_MS = 60_000;
+
 export function OfflineProvider({ children }: { children: React.ReactNode }) {
   const [ready, setReady] = useState(false);
   const [isOnline, setIsOnline] = useState(true);
@@ -44,8 +46,8 @@ export function OfflineProvider({ children }: { children: React.ReactNode }) {
   }, []);
 
   const syncNow = useCallback(
-    async (eventId?: string) => {
-      const result = await runSync(eventId);
+    async (opts?: SyncOpts) => {
+      const result = await runSync(opts);
       await refreshStatuses();
       return result;
     },
@@ -81,7 +83,7 @@ export function OfflineProvider({ children }: { children: React.ReactNode }) {
       const online = Boolean(state.isConnected && state.isInternetReachable !== false);
       setIsOnline(online);
       if (online) {
-        syncNow().catch(() => undefined);
+        syncNow({ pull: false }).catch(() => undefined);
       }
     });
     return () => unsub();
@@ -90,13 +92,23 @@ export function OfflineProvider({ children }: { children: React.ReactNode }) {
   useEffect(() => {
     const onAppState = (next: AppStateStatus) => {
       if (next === 'active') {
-        syncNow().catch(() => undefined);
+        syncNow({ pull: false }).catch(() => undefined);
       }
     };
     const sub = AppState.addEventListener('change', onAppState);
     return () => sub.remove();
   }, [syncNow]);
 
+  const hasPacks = Object.values(statusByEvent).some((s) => s.enabled);
+
+  useEffect(() => {
+    if (!ready || !isOnline || !hasPacks) return;
+    const id = setInterval(() => {
+      syncNow({ pull: false }).catch(() => undefined);
+    }, AUTO_SYNC_MS);
+    return () => clearInterval(id);
+  }, [ready, isOnline, hasPacks, syncNow]);
+
   const value = useMemo(
     () => ({
       ready,
diff --git a/src/offline/checkInService.ts b/src/offline/checkInService.ts
index 2eb8dd0..87fffad 100644
--- a/src/offline/checkInService.ts
+++ b/src/offline/checkInService.ts
@@ -1,16 +1,18 @@
 import NetInfo from '@react-native-community/netinfo';
 import { v4 as uuidv4 } from 'uuid';
 import { attendancesApi } from '../api/attendances';
-import type { AttendanceCheckInResult } from '../api/types';
+import type { AssignBlankProfile, AttendanceCheckInResult } from '../api/types';
 import { getDeviceId } from './deviceId';
 import {
   applyLocalCheckIn,
-  countPendingForSession,
+  applyLocalProfile,
+  applyLocalUndo,
+  deleteOutbox,
+  findLatestPendingOutboxForParticipant,
   getOfflineParticipant,
   getOfflineSession,
   insertOutbox,
   isOfflinePackActive,
-  updateParticipantFromSync,
 } from './repos';
 
 export type CheckInServiceResult =
@@ -22,17 +24,27 @@ async function isOnline(): Promise<boolean> {
   return Boolean(state.isConnected && state.isInternetReachable !== false);
 }
 
+function displayNameFromProfile(profile: AssignBlankProfile, fallback?: string | null) {
+  const fromNames = [profile.firstName, profile.lastName].filter(Boolean).join(' ').trim();
+  return fromNames || profile.email || fallback || 'Participant';
+}
+
 async function queueLocalCheckIn(opts: {
   eventId: string;
   attendanceId: string;
   attendanceName: string;
   participantId: string;
+  profile?: AssignBlankProfile;
 }): Promise<CheckInServiceResult> {
   const session = await getOfflineSession(opts.attendanceId);
   if (!session) {
     return { ok: false, error: 'Offline pack missing this attendance session. Refresh offline data.' };
   }
 
+  if (opts.profile && session.allowAssignBlank !== 1) {
+    return { ok: false, error: 'Assign a Blank is not enabled for this attendance session.' };
+  }
+
   const participant = await getOfflineParticipant(opts.attendanceId, opts.participantId);
   if (!participant) {
     return {
@@ -57,10 +69,16 @@ async function queueLocalCheckIn(opts: {
     participantId: opts.participantId,
     checkedInAt,
     deviceId,
+    profile: opts.profile ?? null,
   });
+  if (opts.profile) {
+    await applyLocalProfile(opts.attendanceId, opts.participantId, opts.profile);
+  }
   await applyLocalCheckIn(opts.attendanceId, opts.participantId, checkedInAt);
 
   const nextCount = participant.checkInCount + 1;
+  const email = opts.profile?.email ?? participant.email ?? '';
+  const phone = opts.profile?.phone ?? participant.phone ?? '';
   return {
     ok: true,
     pendingSync: true,
@@ -68,9 +86,11 @@ async function queueLocalCheckIn(opts: {
       attendanceId: opts.attendanceId,
       attendanceName: opts.attendanceName || session.name,
       participantId: opts.participantId,
-      displayName: participant.displayName,
-      email: participant.email || '',
-      phone: participant.phone || '',
+      displayName: opts.profile
+        ? displayNameFromProfile(opts.profile, participant.displayName)
+        : participant.displayName,
+      email,
+      phone,
       checkInCount: nextCount,
       lastCheckedInAt: checkedInAt,
       allowDuplicateCheckIn: allowDuplicate,
@@ -80,7 +100,7 @@ async function queueLocalCheckIn(opts: {
 }
 
 /**
- * Check-in: live API when online with empty outbox; otherwise local outbox.
+ * Check-in: always local outbox when Offline is enabled; live API otherwise.
  */
 export async function performAppCheckIn(opts: {
   eventId: string;
@@ -89,15 +109,12 @@ export async function performAppCheckIn(opts: {
   participantId: string;
 }): Promise<CheckInServiceResult> {
   const packActive = await isOfflinePackActive(opts.eventId);
-  const pending = await countPendingForSession(opts.attendanceId);
-  const online = await isOnline();
-
-  if (packActive && (!online || pending > 0)) {
+  if (packActive) {
     return queueLocalCheckIn(opts);
   }
 
+  const online = await isOnline();
   if (!online) {
-    if (packActive) return queueLocalCheckIn(opts);
     return {
       ok: false,
       error: 'You are offline. Enable Offline for this event first to check in without internet.',
@@ -106,21 +123,136 @@ export async function performAppCheckIn(opts: {
 
   const res = await attendancesApi.checkIn(opts.eventId, opts.attendanceId, opts.participantId);
   if (res.error || !res.data) {
-    // Network flake after we thought we were online — fall back to outbox if pack exists
-    if (res.status === 0 && packActive) {
-      return queueLocalCheckIn(opts);
-    }
     return { ok: false, error: res.error || 'Check-in failed' };
   }
 
-  if (packActive) {
-    await updateParticipantFromSync(
-      opts.attendanceId,
-      opts.participantId,
-      res.data.checkInCount,
-      res.data.lastCheckedInAt,
-    );
-  }
-
+  return { ok: true, result: res.data, pendingSync: false };
+}
+
+export async function performAppAssignBlank(opts: {
+  eventId: string;
+  attendanceId: string;
+  attendanceName: string;
+  participantId: string;
+  profile: AssignBlankProfile;
+}): Promise<CheckInServiceResult> {
+  const firstName = opts.profile.firstName.trim();
+  if (!firstName) {
+    return { ok: false, error: 'First name is required' };
+  }
+  const profile: AssignBlankProfile = {
+    firstName,
+    lastName: (opts.profile.lastName || '').trim(),
+    email: (opts.profile.email || '').trim().toLowerCase(),
+    phone: (opts.profile.phone || '').trim(),
+  };
+
+  const packActive = await isOfflinePackActive(opts.eventId);
+  if (packActive) {
+    return queueLocalCheckIn({ ...opts, profile });
+  }
+
+  const online = await isOnline();
+  if (!online) {
+    return {
+      ok: false,
+      error: 'You are offline. Enable Offline for this event first to assign a blank badge.',
+    };
+  }
+
+  const res = await attendancesApi.assignBlank(opts.eventId, opts.attendanceId, {
+    participantId: opts.participantId,
+    ...profile,
+  });
+  if (res.error || !res.data) {
+    return { ok: false, error: res.error || 'Assign blank failed' };
+  }
+
+  return { ok: true, result: res.data, pendingSync: false };
+}
+
+export async function performAppUndoCheckIn(opts: {
+  eventId: string;
+  attendanceId: string;
+  attendanceName: string;
+  participantId: string;
+}): Promise<CheckInServiceResult> {
+  const packActive = await isOfflinePackActive(opts.eventId);
+  if (packActive) {
+    const session = await getOfflineSession(opts.attendanceId);
+    if (!session) {
+      return { ok: false, error: 'Offline pack missing this attendance session. Refresh offline data.' };
+    }
+    const participant = await getOfflineParticipant(opts.attendanceId, opts.participantId);
+    if (!participant) {
+      return {
+        ok: false,
+        error: 'Participant not in offline pack. Refresh offline data while online.',
+      };
+    }
+    if (participant.alreadyCheckedIn !== 1 || participant.checkInCount < 1) {
+      return { ok: false, error: 'Participant is not checked in' };
+    }
+
+    const latest = await findLatestPendingOutboxForParticipant(
+      opts.attendanceId,
+      opts.participantId,
+    );
+    await applyLocalUndo(opts.attendanceId, opts.participantId);
+
+    let pendingSync = false;
+    if (latest && latest.action !== 'undo' && !latest.profile) {
+      await deleteOutbox(latest.clientOpId);
+    } else {
+      const clientOpId = uuidv4();
+      const deviceId = await getDeviceId();
+      await insertOutbox({
+        clientOpId,
+        eventId: opts.eventId,
+        attendanceId: opts.attendanceId,
+        participantId: opts.participantId,
+        checkedInAt: new Date().toISOString(),
+        deviceId,
+        action: 'undo',
+      });
+      pendingSync = true;
+    }
+
+    const nextCount = Math.max(0, participant.checkInCount - 1);
+    return {
+      ok: true,
+      pendingSync,
+      result: {
+        attendanceId: opts.attendanceId,
+        attendanceName: opts.attendanceName || session.name,
+        participantId: opts.participantId,
+        displayName: participant.displayName,
+        email: participant.email ?? '',
+        phone: participant.phone ?? '',
+        checkInCount: nextCount,
+        lastCheckedInAt: nextCount > 0 ? participant.lastCheckedInAt : null,
+        allowDuplicateCheckIn: session.allowDuplicateCheckIn === 1,
+        alreadyCheckedIn: nextCount > 0,
+      },
+    };
+  }
+
+  const online = await isOnline();
+  if (!online) {
+    return {
+      ok: false,
+      error: 'You are offline. Enable Offline for this event first to undo a check-in.',
+    };
+  }
+
+  const res = await attendancesApi.undoCheckIn(opts.eventId, opts.attendanceId, opts.participantId);
+  if (res.error || !res.data) {
+    const err =
+      res.status === 404
+        ? 'Undo API not found on this server. Point the app at a backend that includes POST .../undo-check-in (restart local backend, or deploy it).'
+        : res.error || 'Undo check-in failed';
+    return { ok: false, error: err };
+  }
+
   return { ok: true, result: res.data, pendingSync: false };
 }
diff --git a/src/offline/db.ts b/src/offline/db.ts
index 32791a2..6d7bca1 100644
--- a/src/offline/db.ts
+++ b/src/offline/db.ts
@@ -26,6 +26,7 @@ CREATE TABLE IF NOT EXISTS offline_sessions (
   name TEXT NOT NULL,
   status TEXT NOT NULL,
   allow_duplicate_check_in INTEGER NOT NULL DEFAULT 0,
+  allow_assign_blank INTEGER NOT NULL DEFAULT 0,
   FOREIGN KEY (event_id) REFERENCES offline_events(id) ON DELETE CASCADE
 );
 
@@ -59,6 +60,8 @@ CREATE TABLE IF NOT EXISTS outbox (
   device_id TEXT NOT NULL,
   status TEXT NOT NULL,
   last_error TEXT,
+  profile_json TEXT,
+  action TEXT NOT NULL DEFAULT 'check_in',
   created_at TEXT NOT NULL,
   updated_at TEXT NOT NULL
 );
@@ -68,6 +71,14 @@ CREATE INDEX IF NOT EXISTS idx_outbox_event ON outbox(event_id, status);
 CREATE INDEX IF NOT EXISTS idx_outbox_session ON outbox(attendance_id, status);
 `;
 
+async function ensureColumn(instance: DB, table: string, column: string, ddl: string): Promise<void> {
+  const res = await instance.execute(`PRAGMA table_info(${table})`);
+  const has = res.rows.some((r) => String(r.name) === column);
+  if (!has) {
+    await instance.execute(`ALTER TABLE ${table} ADD COLUMN ${ddl}`);
+  }
+}
+
 export async function getDb(): Promise<DB> {
   if (db) return db;
   if (!readyPromise) {
@@ -80,6 +91,19 @@ export async function getDb(): Promise<DB> {
           .filter(Boolean)
           .map((s) => [`${s};`] as [string]),
       );
+      await ensureColumn(
+        instance,
+        'offline_sessions',
+        'allow_assign_blank',
+        'allow_assign_blank INTEGER NOT NULL DEFAULT 0',
+      );
+      await ensureColumn(instance, 'outbox', 'profile_json', 'profile_json TEXT');
+      await ensureColumn(
+        instance,
+        'outbox',
+        'action',
+        "action TEXT NOT NULL DEFAULT 'check_in'",
+      );
       db = instance;
       return instance;
     })();
diff --git a/src/offline/repos.ts b/src/offline/repos.ts
index 955d711..74e8b5c 100644
--- a/src/offline/repos.ts
+++ b/src/offline/repos.ts
@@ -5,8 +5,10 @@ import type {
   OfflineEventRow,
   OfflineParticipantRow,
   OfflineSessionRow,
+  OutboxAction,
   OutboxRow,
   OutboxStatus,
+  AssignBlankProfile,
 } from './types';
 
 function nowIso() {
@@ -87,14 +89,15 @@ export async function replaceSessionsForEvent(
   await db.execute(`DELETE FROM offline_sessions WHERE event_id = ?`, [eventId]);
   for (const s of sessions) {
     await db.execute(
-      `INSERT INTO offline_sessions (id, event_id, name, status, allow_duplicate_check_in)
-       VALUES (?, ?, ?, ?, ?)`,
+      `INSERT INTO offline_sessions (id, event_id, name, status, allow_duplicate_check_in, allow_assign_blank)
+       VALUES (?, ?, ?, ?, ?, ?)`,
       [
         s._id,
         eventId,
         s.name,
         s.status,
         s.settings?.allowDuplicateCheckIn ? 1 : 0,
+        s.settings?.allowAssignBlank ? 1 : 0,
       ],
     );
   }
@@ -112,6 +115,7 @@ export async function listOfflineSessions(eventId: string): Promise<OfflineSessi
     name: String(row.name),
     status: String(row.status),
     allowDuplicateCheckIn: Number(row.allow_duplicate_check_in) || 0,
+    allowAssignBlank: Number(row.allow_assign_blank) || 0,
   }));
 }
 
@@ -126,6 +130,7 @@ export async function getOfflineSession(attendanceId: string): Promise<OfflineSe
     name: String(row.name),
     status: String(row.status),
     allowDuplicateCheckIn: Number(row.allow_duplicate_check_in) || 0,
+    allowAssignBlank: Number(row.allow_assign_blank) || 0,
   };
 }
 
@@ -220,6 +225,36 @@ export async function getOfflineParticipant(
   return mapParticipant(row as Record<string, unknown>);
 }
 
+export async function applyLocalProfile(
+  attendanceId: string,
+  participantId: string,
+  profile: AssignBlankProfile,
+): Promise<void> {
+  const db = await getDb();
+  const displayName =
+    [profile.firstName, profile.lastName].filter(Boolean).join(' ').trim() ||
+    profile.email ||
+    'Participant';
+  await db.execute(
+    `UPDATE offline_participants
+     SET first_name = ?,
+         last_name = ?,
+         email = ?,
+         phone = ?,
+         display_name = ?
+     WHERE attendance_id = ? AND participant_id = ?`,
+    [
+      profile.firstName,
+      profile.lastName ?? '',
+      profile.email ?? '',
+      profile.phone ?? '',
+      displayName,
+      attendanceId,
+      participantId,
+    ],
+  );
+}
+
 export async function applyLocalCheckIn(
   attendanceId: string,
   participantId: string,
@@ -236,6 +271,18 @@ export async function applyLocalCheckIn(
   );
 }
 
+export async function applyLocalUndo(attendanceId: string, participantId: string): Promise<void> {
+  const db = await getDb();
+  await db.execute(
+    `UPDATE offline_participants
+     SET already_checked_in = CASE WHEN check_in_count <= 1 THEN 0 ELSE 1 END,
+         last_checked_in_at = CASE WHEN check_in_count <= 1 THEN NULL ELSE last_checked_in_at END,
+         check_in_count = MAX(0, check_in_count - 1)
+     WHERE attendance_id = ? AND participant_id = ?`,
+    [attendanceId, participantId],
+  );
+}
+
 export async function updateParticipantFromSync(
   attendanceId: string,
   participantId: string,
@@ -260,14 +307,16 @@ export async function insertOutbox(row: {
   participantId: string;
   checkedInAt: string;
   deviceId: string;
+  profile?: AssignBlankProfile | null;
+  action?: OutboxAction;
 }): Promise<void> {
   const db = await getDb();
   const ts = nowIso();
   await db.execute(
     `INSERT INTO outbox (
       client_op_id, event_id, attendance_id, participant_id, checked_in_at,
-      device_id, status, last_error, created_at, updated_at
-    ) VALUES (?, ?, ?, ?, ?, ?, 'pending', NULL, ?, ?)`,
+      device_id, status, last_error, profile_json, action, created_at, updated_at
+    ) VALUES (?, ?, ?, ?, ?, ?, 'pending', NULL, ?, ?, ?, ?)`,
     [
       row.clientOpId,
       row.eventId,
@@ -275,12 +324,29 @@ export async function insertOutbox(row: {
       row.participantId,
       row.checkedInAt,
       row.deviceId,
+      row.profile ? JSON.stringify(row.profile) : null,
+      row.action || 'check_in',
       ts,
       ts,
     ],
   );
 }
 
+function parseOutboxAction(raw: unknown): OutboxAction {
+  return String(raw) === 'undo' ? 'undo' : 'check_in';
+}
+
+function parseProfileJson(raw: unknown): AssignBlankProfile | null {
+  if (raw == null || raw === '') return null;
+  try {
+    const parsed = JSON.parse(String(raw)) as AssignBlankProfile;
+    if (!parsed || typeof parsed.firstName !== 'string') return null;
+    return parsed;
+  } catch {
+    return null;
+  }
+}
+
 function mapOutbox(row: Record<string, unknown>): OutboxRow {
   return {
     clientOpId: String(row.client_op_id),
@@ -293,22 +359,50 @@ function mapOutbox(row: Record<string, unknown>): OutboxRow {
     lastError: row.last_error != null ? String(row.last_error) : null,
     createdAt: String(row.created_at),
     updatedAt: String(row.updated_at),
+    profile: parseProfileJson(row.profile_json),
+    action: parseOutboxAction(row.action),
   };
 }
 
-export async function listPendingOutbox(eventId?: string): Promise<OutboxRow[]> {
+export async function listPendingOutbox(scope?: {
+  eventId?: string;
+  attendanceId?: string;
+}): Promise<OutboxRow[]> {
   const db = await getDb();
-  const res = eventId
+  const res = scope?.attendanceId
     ? await db.execute(
-        `SELECT * FROM outbox WHERE event_id = ? AND status IN ('pending', 'syncing') ORDER BY created_at ASC`,
-        [eventId],
+        `SELECT * FROM outbox WHERE attendance_id = ? AND status IN ('pending', 'syncing') ORDER BY created_at ASC`,
+        [scope.attendanceId],
       )
-    : await db.execute(
-        `SELECT * FROM outbox WHERE status IN ('pending', 'syncing') ORDER BY created_at ASC`,
-      );
+    : scope?.eventId
+      ? await db.execute(
+          `SELECT * FROM outbox WHERE event_id = ? AND status IN ('pending', 'syncing') ORDER BY created_at ASC`,
+          [scope.eventId],
+        )
+      : await db.execute(
+          `SELECT * FROM outbox WHERE status IN ('pending', 'syncing') ORDER BY created_at ASC`,
+        );
   return res.rows.map((r) => mapOutbox(r as Record<string, unknown>));
 }
 
+/** Overlay leftover outbox rows onto the local roster after a server pull. */
+export async function reapplyPendingOutboxToRoster(scope?: {
+  eventId?: string;
+  attendanceId?: string;
+}): Promise<void> {
+  const pending = await listPendingOutbox(scope);
+  for (const row of pending) {
+    if (row.action === 'undo') {
+      await applyLocalUndo(row.attendanceId, row.participantId);
+      continue;
+    }
+    if (row.profile) {
+      await applyLocalProfile(row.attendanceId, row.participantId, row.profile);
+    }
+    await applyLocalCheckIn(row.attendanceId, row.participantId, row.checkedInAt);
+  }
+}
+
 export async function listConflictOutbox(eventId: string): Promise<OutboxRow[]> {
   const db = await getDb();
   const res = await db.execute(
@@ -340,6 +434,27 @@ export async function countPendingForSession(attendanceId: string): Promise<numb
   return Number(res.rows[0]?.c) || 0;
 }
 
+export async function findLatestPendingOutboxForParticipant(
+  attendanceId: string,
+  participantId: string,
+): Promise<OutboxRow | null> {
+  const db = await getDb();
+  const res = await db.execute(
+    `SELECT * FROM outbox
+     WHERE attendance_id = ? AND participant_id = ? AND status IN ('pending', 'syncing')
+     ORDER BY created_at DESC LIMIT 1`,
+    [attendanceId, participantId],
+  );
+  const row = res.rows[0];
+  if (!row) return null;
+  return mapOutbox(row as Record<string, unknown>);
+}
+
+export async function deleteOutbox(clientOpId: string): Promise<void> {
+  const db = await getDb();
+  await db.execute(`DELETE FROM outbox WHERE client_op_id = ?`, [clientOpId]);
+}
+
 export async function markOutboxStatus(
   clientOpId: string,
   status: OutboxStatus,
diff --git a/src/offline/syncEngine.ts b/src/offline/syncEngine.ts
index 1831ed1..9643bb8 100644
--- a/src/offline/syncEngine.ts
+++ b/src/offline/syncEngine.ts
@@ -1,16 +1,33 @@
 import NetInfo from '@react-native-community/netinfo';
 import { attendancesApi } from '../api/attendances';
 import { getDeviceId } from './deviceId';
-import { refreshSessionRoster } from './download';
+import { refreshOfflinePack, refreshSessionRoster } from './download';
 import {
+  getOfflineEvent,
+  getOfflineSession,
+  listOfflineEventIds,
   listPendingOutbox,
   markOutboxStatus,
   markOutboxSyncing,
+  reapplyPendingOutboxToRoster,
   setEventLastSyncedAt,
   updateParticipantFromSync,
 } from './repos';
 import type { SyncOpResult } from './types';
 
+export type SyncOpts = {
+  eventId?: string;
+  attendanceId?: string;
+  pull?: boolean;
+};
+
+export type SyncResult = {
+  ok: boolean;
+  flushed: number;
+  pulled: boolean;
+  error?: string;
+};
+
 type SyncListener = (state: { syncing: boolean; lastError: string | null }) => void;
 
 let syncing = false;
@@ -31,16 +48,75 @@ export function isSyncEngineRunning(): boolean {
   return syncing;
 }
 
+export function formatSyncAlert(result: SyncResult): string {
+  if (!result.ok && result.error && result.flushed === 0 && !result.pulled) {
+    return result.error;
+  }
+  const bits: string[] = [];
+  if (result.flushed > 0) {
+    bits.push(`Synced ${result.flushed} check-in${result.flushed === 1 ? '' : 's'}`);
+  }
+  if (result.pulled) {
+    bits.push(result.flushed > 0 ? 'roster refreshed' : 'Roster updated');
+  }
+  if (!bits.length) {
+    return result.error || 'Already up to date.';
+  }
+  const msg = bits.join(' · ');
+  return result.error ? `${msg}. ${result.error}` : msg;
+}
+
+function mergeSyncOpts(a: SyncOpts, b: SyncOpts): SyncOpts {
+  const pull = Boolean(a.pull || b.pull);
+  if (!a.eventId || !b.eventId || a.eventId !== b.eventId) {
+    return { pull };
+  }
+  if (!a.attendanceId || !b.attendanceId || a.attendanceId !== b.attendanceId) {
+    return { eventId: a.eventId, pull };
+  }
+  return { eventId: a.eventId, attendanceId: a.attendanceId, pull };
+}
+
+type Deferred = {
+  promise: Promise<SyncResult>;
+  resolve: (r: SyncResult) => void;
+};
+
+function createDeferred(): Deferred {
+  let resolve: (r: SyncResult) => void = () => undefined;
+  const promise = new Promise<SyncResult>((res) => {
+    resolve = res;
+  });
+  return { promise, resolve };
+}
+
+let running = false;
+let queuedOpts: SyncOpts | null = null;
+let queuedDeferred: Deferred | null = null;
+
 async function flushGroup(
   eventId: string,
   attendanceId: string,
-  ops: { clientOpId: string; participantId: string; checkedInAt: string }[],
+  ops: {
+    clientOpId: string;
+    participantId: string;
+    checkedInAt: string;
+    profile?: { firstName: string; lastName?: string; email?: string; phone?: string } | null;
+    action?: 'check_in' | 'undo';
+  }[],
   deviceId: string,
+  refreshRoster: boolean,
 ): Promise<string | null> {
   await markOutboxSyncing(ops.map((o) => o.clientOpId));
   const res = await attendancesApi.syncCheckIns(eventId, attendanceId, {
     deviceId,
-    operations: ops,
+    operations: ops.map((o) => ({
+      clientOpId: o.clientOpId,
+      participantId: o.participantId,
+      checkedInAt: o.checkedInAt,
+      ...(o.profile ? { profile: o.profile } : {}),
+      ...(o.action === 'undo' ? { action: 'undo' as const } : {}),
+    })),
   });
 
   if (res.error || !res.data) {
@@ -88,38 +164,70 @@ async function flushGroup(
     }
   }
 
-  // Light roster refresh to pick up other devices
-  await refreshSessionRoster(eventId, attendanceId);
+  if (refreshRoster) {
+    const rr = await refreshSessionRoster(eventId, attendanceId);
+    if (rr.ok) {
+      await reapplyPendingOutboxToRoster({ attendanceId });
+    }
+  }
   return null;
 }
 
-/**
- * Flush pending outbox. Optionally scope to one event.
- */
-export async function runSync(eventId?: string): Promise<{
-  ok: boolean;
-  flushed: number;
-  error?: string;
-}> {
-  if (syncing) {
-    return { ok: false, flushed: 0, error: 'Sync already in progress' };
+async function pullSheets(opts: SyncOpts): Promise<{ eventIds: string[]; error?: string }> {
+  if (opts.attendanceId) {
+    let eventId = opts.eventId;
+    if (!eventId) {
+      const session = await getOfflineSession(opts.attendanceId);
+      eventId = session?.eventId;
+    }
+    if (!eventId) {
+      return { eventIds: [], error: 'Offline pack missing this attendance session.' };
+    }
+    const res = await refreshSessionRoster(eventId, opts.attendanceId);
+    if (!res.ok) {
+      return { eventIds: [], error: res.error };
+    }
+    await reapplyPendingOutboxToRoster({ attendanceId: opts.attendanceId });
+    return { eventIds: [eventId] };
   }
 
+  const ids = opts.eventId ? [opts.eventId] : await listOfflineEventIds();
+  let lastError: string | undefined;
+  const eventIds: string[] = [];
+  for (const id of ids) {
+    const event = await getOfflineEvent(id);
+    if (!event) continue;
+    const res = await refreshOfflinePack({
+      _id: event.id,
+      name: event.name,
+      startDate: event.startDate ?? undefined,
+      endDate: event.endDate ?? undefined,
+      location: event.location ?? undefined,
+    });
+    if (!res.ok) {
+      lastError = res.error;
+      continue;
+    }
+    eventIds.push(id);
+    await reapplyPendingOutboxToRoster({ eventId: id });
+  }
+  return { eventIds, error: lastError };
+}
+
+async function executeSync(opts: SyncOpts): Promise<SyncResult> {
   const net = await NetInfo.fetch();
   if (!net.isConnected || net.isInternetReachable === false) {
-    return { ok: false, flushed: 0, error: 'No internet connection' };
+    return { ok: false, flushed: 0, pulled: false, error: 'No internet connection' };
   }
 
-  syncing = true;
-  emit(null);
-
-  try {
-    const pending = await listPendingOutbox(eventId);
-    if (!pending.length) {
-      if (eventId) await setEventLastSyncedAt(eventId, new Date().toISOString());
-      return { ok: true, flushed: 0 };
-    }
+  const scope = { eventId: opts.eventId, attendanceId: opts.attendanceId };
+  const pending = await listPendingOutbox(scope);
+  const pull = Boolean(opts.pull);
+  let flushed = 0;
+  let lastError: string | null = null;
+  const touchedEvents = new Set<string>();
 
+  if (pending.length) {
     const deviceId = await getDeviceId();
     const groups = new Map<string, typeof pending>();
     for (const row of pending) {
@@ -129,14 +237,9 @@ export async function runSync(eventId?: string): Promise<{
       groups.set(key, list);
     }
 
-    let flushed = 0;
-    let lastError: string | null = null;
-    const touchedEvents = new Set<string>();
-
     for (const [key, rows] of groups) {
       const [eid, aid] = key.split('::');
       touchedEvents.add(eid);
-      // Chunk 200
       for (let i = 0; i < rows.length; i += 200) {
         const chunk = rows.slice(i, i + 200);
         const err = await flushGroup(
@@ -146,29 +249,80 @@ export async function runSync(eventId?: string): Promise<{
             clientOpId: r.clientOpId,
             participantId: r.participantId,
             checkedInAt: r.checkedInAt,
+            profile: r.profile,
+            action: r.action,
           })),
           deviceId,
+          !pull,
         );
         if (err) lastError = err;
         else flushed += chunk.length;
       }
     }
-
-    const ts = new Date().toISOString();
-    for (const eid of touchedEvents) {
-      await setEventLastSyncedAt(eid, ts);
-    }
-
-    emit(lastError);
-    return lastError
-      ? { ok: false, flushed, error: lastError }
-      : { ok: true, flushed };
-  } catch (e) {
-    const msg = e instanceof Error ? e.message : 'Sync failed';
-    emit(msg);
-    return { ok: false, flushed: 0, error: msg };
-  } finally {
-    syncing = false;
-    emit(null);
   }
+
+  let pulled = false;
+  if (pull) {
+    const pullResult = await pullSheets(opts);
+    for (const id of pullResult.eventIds) touchedEvents.add(id);
+    if (pullResult.error) {
+      lastError = lastError || pullResult.error;
+    }
+    if (pullResult.eventIds.length) {
+      pulled = true;
+    }
+  }
+
+  const ts = new Date().toISOString();
+  for (const eid of touchedEvents) {
+    await setEventLastSyncedAt(eid, ts);
+  }
+
+  emit(lastError);
+  return lastError
+    ? { ok: false, flushed, pulled, error: lastError }
+    : { ok: true, flushed, pulled };
+}
+
+/**
+ * Flush pending outbox, optionally pull latest sheets.
+ * Overlapping calls are queued and merged (widest scope + pull wins).
+ */
+export function runSync(opts: SyncOpts = {}): Promise<SyncResult> {
+  if (running) {
+    queuedOpts = queuedOpts ? mergeSyncOpts(queuedOpts, opts) : { ...opts };
+    if (!queuedDeferred) queuedDeferred = createDeferred();
+    return queuedDeferred.promise;
+  }
+
+  running = true;
+  syncing = true;
+  emit(null);
+
+  return (async () => {
+    try {
+      const first = await executeSync(opts);
+      while (queuedOpts) {
+        const next = queuedOpts;
+        const deferred = queuedDeferred;
+        queuedOpts = null;
+        queuedDeferred = null;
+        const queuedResult = await executeSync(next);
+        deferred?.resolve(queuedResult);
+      }
+      return first;
+    } catch (e) {
+      const msg = e instanceof Error ? e.message : 'Sync failed';
+      const fail: SyncResult = { ok: false, flushed: 0, pulled: false, error: msg };
+      queuedDeferred?.resolve(fail);
+      queuedOpts = null;
+      queuedDeferred = null;
+      emit(msg);
+      return fail;
+    } finally {
+      running = false;
+      syncing = false;
+      emit(null);
+    }
+  })();
 }
diff --git a/src/offline/types.ts b/src/offline/types.ts
index eb94604..d107aef 100644
--- a/src/offline/types.ts
+++ b/src/offline/types.ts
@@ -17,6 +17,7 @@ export type OfflineSessionRow = {
   name: string;
   status: string;
   allowDuplicateCheckIn: number;
+  allowAssignBlank: number;
 };
 
 export type OfflineParticipantRow = {
@@ -33,6 +34,15 @@ export type OfflineParticipantRow = {
   lastCheckedInAt: string | null;
 };
 
+export type AssignBlankProfile = {
+  firstName: string;
+  lastName?: string;
+  email?: string;
+  phone?: string;
+};
+
+export type OutboxAction = 'check_in' | 'undo';
+
 export type OutboxRow = {
   clientOpId: string;
   eventId: string;
@@ -44,6 +54,8 @@ export type OutboxRow = {
   lastError: string | null;
   createdAt: string;
   updatedAt: string;
+  profile: AssignBlankProfile | null;
+  action: OutboxAction;
 };
 
 export type SyncOpResultStatus = 'applied' | 'duplicate' | 'conflict' | 'rejected';
diff --git a/src/screens/AssignBlankScreen.tsx b/src/screens/AssignBlankScreen.tsx
new file mode 100644
index 0000000..a4ce580
--- /dev/null
+++ b/src/screens/AssignBlankScreen.tsx
@@ -0,0 +1,242 @@
+import React, { useState } from 'react';
+import {
+  Alert,
+  KeyboardAvoidingView,
+  Platform,
+  Pressable,
+  ScrollView,
+  StyleSheet,
+  Text,
+  View,
+} from 'react-native';
+import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import type { NativeStackScreenProps } from '@react-navigation/native-stack';
+import type { AttendanceCheckInResult } from '../api/types';
+import { CheckInResultModal } from '../components/CheckInResultModal';
+import type { RootStackParamList } from '../navigation/types';
+import { performAppAssignBlank, performAppUndoCheckIn } from '../offline/checkInService';
+import { useOffline } from '../offline/OfflineContext';
+import { colors, spacing, typography } from '../theme';
+import { AppIcon, PrimaryButton, TextField } from '../components/ui';
+
+type Props = NativeStackScreenProps<RootStackParamList, 'AssignBlank'>;
+
+export function AssignBlankScreen({ navigation, route }: Props) {
+  const {
+    eventId,
+    eventName,
+    attendanceId,
+    attendanceName,
+    participantId,
+    firstName: initialFirst,
+    lastName: initialLast,
+    email: initialEmail,
+    phone: initialPhone,
+  } = route.params;
+  const insets = useSafeAreaInsets();
+  const { refreshStatuses } = useOffline();
+
+  const [firstName, setFirstName] = useState(initialFirst || '');
+  const [lastName, setLastName] = useState(initialLast || '');
+  const [email, setEmail] = useState(initialEmail || '');
+  const [phone, setPhone] = useState(initialPhone || '');
+  const [saving, setSaving] = useState(false);
+  const [result, setResult] = useState<AttendanceCheckInResult | null>(null);
+  const [resultError, setResultError] = useState<string | null>(null);
+  const [pendingSync, setPendingSync] = useState(false);
+  const [modalVisible, setModalVisible] = useState(false);
+  const [undoLoading, setUndoLoading] = useState(false);
+
+  const save = async () => {
+    if (!firstName.trim()) {
+      setResult(null);
+      setResultError('First name is required');
+      setPendingSync(false);
+      setModalVisible(true);
+      return;
+    }
+    setSaving(true);
+    const outcome = await performAppAssignBlank({
+      eventId,
+      attendanceId,
+      attendanceName,
+      participantId,
+      profile: { firstName, lastName, email, phone },
+    });
+    setSaving(false);
+    if (!outcome.ok) {
+      setResult(null);
+      setResultError(outcome.error);
+      setPendingSync(false);
+    } else {
+      setResult(outcome.result);
+      setResultError(null);
+      setPendingSync(outcome.pendingSync);
+      refreshStatuses().catch(() => undefined);
+    }
+    setModalVisible(true);
+  };
+
+  const closeModal = () => {
+    if (undoLoading) return;
+    setModalVisible(false);
+    if (result && !resultError) {
+      navigation.goBack();
+      return;
+    }
+    setResult(null);
+    setResultError(null);
+    setPendingSync(false);
+  };
+
+  const handleUndo = async () => {
+    if (!result) return;
+    setUndoLoading(true);
+    const outcome = await performAppUndoCheckIn({
+      eventId,
+      attendanceId,
+      attendanceName,
+      participantId: result.participantId,
+    });
+    setUndoLoading(false);
+    if (!outcome.ok) {
+      Alert.alert('Undo failed', outcome.error);
+      return;
+    }
+    setModalVisible(false);
+    setResult(null);
+    setResultError(null);
+    setPendingSync(false);
+    refreshStatuses().catch(() => undefined);
+    navigation.goBack();
+  };
+
+  return (
+    <View style={styles.wrap}>
+      <View style={[styles.header, { paddingTop: insets.top + spacing.md }]}>
+        <View style={styles.headerBg} />
+        <Pressable onPress={() => navigation.goBack()} hitSlop={10} style={styles.backBtn}>
+          <AppIcon name="arrow-back" size={18} color="rgba(255,255,255,0.85)" />
+          <Text style={styles.backLabel} numberOfLines={1}>
+            {eventName}
+          </Text>
+        </Pressable>
+        <Text style={styles.headerTitle}>Assign a Blank</Text>
+        <Text style={styles.headerSubtitle}>{attendanceName}</Text>
+      </View>
+
+      <KeyboardAvoidingView
+        style={styles.flex}
+        behavior={Platform.OS === 'ios' ? 'padding' : undefined}
+      >
+        <ScrollView
+          contentContainerStyle={[
+            styles.form,
+            { paddingBottom: Math.max(insets.bottom, 16) + 24 },
+          ]}
+          keyboardShouldPersistTaps="handled"
+        >
+          <Text style={styles.lead}>
+            Update this spare badge’s details, then save to check the person in.
+          </Text>
+          <TextField
+            label="First name"
+            value={firstName}
+            onChangeText={setFirstName}
+            autoCapitalize="words"
+            autoCorrect={false}
+          />
+          <TextField
+            label="Last name"
+            value={lastName}
+            onChangeText={setLastName}
+            autoCapitalize="words"
+            autoCorrect={false}
+          />
+          <TextField
+            label="Email"
+            value={email}
+            onChangeText={setEmail}
+            keyboardType="email-address"
+            autoCapitalize="none"
+            autoCorrect={false}
+          />
+          <TextField
+            label="Phone"
+            value={phone}
+            onChangeText={setPhone}
+            keyboardType="phone-pad"
+            autoCorrect={false}
+          />
+          <PrimaryButton
+            title="Save and check in"
+            loading={saving}
+            onPress={() => {
+              void save();
+            }}
+          />
+        </ScrollView>
+      </KeyboardAvoidingView>
+
+      <CheckInResultModal
+        visible={modalVisible}
+        result={result}
+        error={resultError}
+        pendingSync={pendingSync}
+        onClose={closeModal}
+        onUndo={result ? handleUndo : undefined}
+        undoLoading={undoLoading}
+      />
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  wrap: { flex: 1, backgroundColor: colors.background },
+  flex: { flex: 1 },
+  header: {
+    paddingHorizontal: spacing.xl,
+    paddingBottom: spacing.lg,
+    overflow: 'hidden',
+  },
+  headerBg: {
+    ...StyleSheet.absoluteFill,
+    backgroundColor: colors.primary,
+    zIndex: 0,
+  },
+  backBtn: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    gap: 8,
+    marginBottom: spacing.md,
+    alignSelf: 'flex-start',
+    zIndex: 1,
+  },
+  backLabel: {
+    color: 'rgba(255,255,255,0.85)',
+    fontSize: 14,
+    fontWeight: '500',
+  },
+  headerTitle: {
+    color: '#fff',
+    fontSize: 20,
+    fontWeight: '700',
+    marginBottom: 4,
+    zIndex: 1,
+  },
+  headerSubtitle: {
+    color: 'rgba(255,255,255,0.90)',
+    fontSize: 14,
+    zIndex: 1,
+  },
+  form: {
+    paddingHorizontal: spacing.lg,
+    paddingTop: spacing.lg,
+    gap: 16,
+  },
+  lead: {
+    ...typography.small,
+    color: colors.muted,
+    marginBottom: 4,
+  },
+});
diff --git a/src/screens/AttendanceSessionsScreen.tsx b/src/screens/AttendanceSessionsScreen.tsx
index ea082a9..e9e4765 100644
--- a/src/screens/AttendanceSessionsScreen.tsx
+++ b/src/screens/AttendanceSessionsScreen.tsx
@@ -15,6 +15,7 @@ import { attendancesApi } from '../api/attendances';
 import type { AttendanceRecord } from '../api/types';
 import type { RootStackParamList } from '../navigation/types';
 import { useOffline } from '../offline/OfflineContext';
+import { formatSyncAlert } from '../offline/syncEngine';
 import {
   dismissConflict,
   getOfflineEvent,
@@ -31,6 +32,13 @@ const SESSION_ICONS: AppIconName[] = ['business-outline', 'people-outline'];
 const CHECKIN_GREEN = '#22C55E';
 const PEOPLE_BLUE = '#60A5FA';
 
+function formatLastSynced(iso?: string | null) {
+  if (!iso) return 'not yet';
+  const d = new Date(iso);
+  if (Number.isNaN(d.getTime())) return 'not yet';
+  return d.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' });
+}
+
 function SessionsHeader({
   eventName,
   onBack,
@@ -39,6 +47,7 @@ function SessionsHeader({
   pendingCount,
   isOnline,
   offlineReady,
+  lastSyncedAt,
 }: {
   eventName: string;
   onBack: () => void;
@@ -47,6 +56,7 @@ function SessionsHeader({
   pendingCount: number;
   isOnline: boolean;
   offlineReady: boolean;
+  lastSyncedAt: string | null;
 }) {
   const insets = useSafeAreaInsets();
 
@@ -85,7 +95,7 @@ function SessionsHeader({
       <Text style={styles.headerSubtitle}>
         {offlineReady
           ? isOnline
-            ? 'Offline pack ready · Select a session'
+            ? `Offline mode · last synced ${formatLastSynced(lastSyncedAt)}`
             : 'Working offline · Select a session'
           : 'Select an attendance session'}
       </Text>
@@ -115,6 +125,41 @@ export function AttendanceSessionsScreen({ navigation, route }: Props) {
   const load = useCallback(async () => {
     setError(null);
 
+    if (await getOfflineEvent(eventId)) {
+      const local = await listOfflineSessions(eventId);
+      if (!local.length) {
+        setError(
+          isOnline
+            ? 'No active attendance sessions.'
+            : 'No offline data for this event. Go online and Enable Offline first.',
+        );
+        setSessions([]);
+        setFromCache(true);
+        return;
+      }
+
+      const mapped: AttendanceRecord[] = [];
+      for (const s of local) {
+        const participants = await listOfflineParticipants(s.id);
+        const unique = participants.filter((p) => p.alreadyCheckedIn).length;
+        const total = participants.reduce((n, p) => n + (p.checkInCount || 0), 0);
+        mapped.push({
+          _id: s.id,
+          name: s.name,
+          status: s.status as 'active' | 'archived',
+          settings: {
+            allowDuplicateCheckIn: s.allowDuplicateCheckIn === 1,
+            allowAssignBlank: s.allowAssignBlank === 1,
+          },
+          uniqueParticipants: unique,
+          totalCheckedIn: total,
+        });
+      }
+      setSessions(mapped);
+      setFromCache(true);
+      return;
+    }
+
     if (isOnline) {
       const res = await attendancesApi.list(eventId);
       if (!res.error && res.data) {
@@ -123,64 +168,35 @@ export function AttendanceSessionsScreen({ navigation, route }: Props) {
         setFromCache(false);
         return;
       }
-      // fall through to cache on failure
-      if (!(await getOfflineEvent(eventId))) {
-        setError(res.error || 'Failed to load sessions');
-        setSessions([]);
-        setFromCache(false);
-        return;
-      }
-    }
-
-    const local = await listOfflineSessions(eventId);
-    if (!local.length) {
-      setError(
-        isOnline
-          ? 'No active attendance sessions.'
-          : 'No offline data for this event. Go online and Enable Offline first.',
-      );
+      setError(res.error || 'Failed to load sessions');
       setSessions([]);
       setFromCache(false);
       return;
     }
 
-    const mapped: AttendanceRecord[] = [];
-    for (const s of local) {
-      const participants = await listOfflineParticipants(s.id);
-      const unique = participants.filter((p) => p.alreadyCheckedIn).length;
-      const total = participants.reduce((n, p) => n + (p.checkInCount || 0), 0);
-      mapped.push({
-        _id: s.id,
-        name: s.name,
-        status: s.status as 'active' | 'archived',
-        settings: { allowDuplicateCheckIn: s.allowDuplicateCheckIn === 1 },
-        uniqueParticipants: unique,
-        totalCheckedIn: total,
-      });
-    }
-    setSessions(mapped);
-    setFromCache(true);
+    setError('No offline data for this event. Go online and Enable Offline first.');
+    setSessions([]);
+    setFromCache(false);
   }, [eventId, isOnline]);
 
   useEffect(() => {
+    const unsub = navigation.addListener('focus', () => {
+      load();
+      refreshStatuses();
+    });
     (async () => {
       setLoading(true);
       await load();
       await refreshStatuses();
       setLoading(false);
     })();
-  }, [load, refreshStatuses]);
+    return unsub;
+  }, [navigation, load, refreshStatuses]);
 
   const handleSync = async () => {
-    const result = await syncNow(eventId);
+    const result = await syncNow({ eventId, pull: true });
     await load();
-    if (!result.ok && result.error) {
-      Alert.alert('Sync', result.error);
-    } else if (result.flushed > 0) {
-      Alert.alert('Sync', `Synced ${result.flushed} check-in${result.flushed === 1 ? '' : 's'}.`);
-    } else {
-      Alert.alert('Sync', 'Nothing pending to sync.');
-    }
+    Alert.alert('Sync', formatSyncAlert(result));
 
     const conflicts = await listConflictOutbox(eventId);
     if (conflicts.length) {
@@ -218,6 +234,7 @@ export function AttendanceSessionsScreen({ navigation, route }: Props) {
             attendanceId: item._id,
             attendanceName: item.name,
             allowDuplicate: Boolean(item.settings?.allowDuplicateCheckIn),
+            allowAssignBlank: Boolean(item.settings?.allowAssignBlank),
           })
         }
       >
@@ -265,6 +282,7 @@ export function AttendanceSessionsScreen({ navigation, route }: Props) {
         pendingCount={status?.pendingCount ?? 0}
         isOnline={isOnline}
         offlineReady={offlineReady}
+        lastSyncedAt={status?.lastSyncedAt ?? null}
       />
 
       {fromCache ? (
diff --git a/src/screens/EventsScreen.tsx b/src/screens/EventsScreen.tsx
index a31eff7..3d2984b 100644
--- a/src/screens/EventsScreen.tsx
+++ b/src/screens/EventsScreen.tsx
@@ -18,6 +18,7 @@ import type { CheckinsEvent } from '../api/types';
 import { useAuth } from '../context/AuthContext';
 import { downloadOfflinePack, refreshOfflinePack } from '../offline/download';
 import { useOffline } from '../offline/OfflineContext';
+import { formatSyncAlert } from '../offline/syncEngine';
 import { listOfflineEvents, listOfflineSessions, removeOfflineEventData } from '../offline/repos';
 import type { RootStackParamList } from '../navigation/types';
 import { colors, radii, shadows, spacing, typography } from '../theme';
@@ -47,6 +48,7 @@ function EventsHeader({
   syncing,
   pendingTotal,
   isOnline,
+  hasOfflinePacks,
 }: {
   userEmail?: string | null;
   onLogout: () => void;
@@ -54,6 +56,7 @@ function EventsHeader({
   syncing: boolean;
   pendingTotal: number;
   isOnline: boolean;
+  hasOfflinePacks: boolean;
 }) {
   const insets = useSafeAreaInsets();
 
@@ -74,7 +77,7 @@ function EventsHeader({
             onPress={onSync}
             hitSlop={10}
             style={styles.syncBtn}
-            disabled={syncing || !isOnline}
+            disabled={syncing || !isOnline || !hasOfflinePacks}
           >
             {syncing ? (
               <ActivityIndicator color="#fff" size="small" />
@@ -191,14 +194,9 @@ export function EventsScreen({ navigation }: Props) {
   };
 
   const handleSync = async () => {
-    const result = await syncNow();
-    if (!result.ok && result.error) {
-      Alert.alert('Sync', result.error);
-    } else if (result.flushed > 0) {
-      Alert.alert('Sync', `Synced ${result.flushed} check-in${result.flushed === 1 ? '' : 's'}.`);
-    } else {
-      Alert.alert('Sync', 'Nothing pending to sync.');
-    }
+    const result = await syncNow({ pull: true });
+    await load();
+    Alert.alert('Sync', formatSyncAlert(result));
   };
 
   const enableOffline = async (item: CheckinsEvent) => {
@@ -285,6 +283,7 @@ export function EventsScreen({ navigation }: Props) {
   };
 
   const pendingTotal = Object.values(statusByEvent).reduce((n, s) => n + s.pendingCount, 0);
+  const hasOfflinePacks = Object.values(statusByEvent).some((s) => s.enabled);
 
   const renderItem = ({ item }: { item: CheckinsEvent }) => {
     const sessionCount = item.attendanceSessionCount;
@@ -390,6 +389,7 @@ export function EventsScreen({ navigation }: Props) {
         syncing={syncing}
         pendingTotal={pendingTotal}
         isOnline={isOnline}
+        hasOfflinePacks={hasOfflinePacks}
       />
 
       {loading ? (
diff --git a/src/screens/ParticipantsScreen.tsx b/src/screens/ParticipantsScreen.tsx
index a3a3126..55580b0 100644
--- a/src/screens/ParticipantsScreen.tsx
+++ b/src/screens/ParticipantsScreen.tsx
@@ -1,6 +1,7 @@
-import React, { useCallback, useEffect, useMemo, useState } from 'react';
+import React, { useCallback, useEffect, useLayoutEffect, useMemo, useState } from 'react';
 import {
   ActivityIndicator,
+  Alert,
   FlatList,
   Pressable,
   StyleSheet,
@@ -13,9 +14,11 @@ import type { NativeStackScreenProps } from '@react-navigation/native-stack';
 import { attendancesApi } from '../api/attendances';
 import type { AttendanceCheckInResult, AttendanceSearchParticipant } from '../api/types';
 import { CheckInResultModal } from '../components/CheckInResultModal';
+import { SwipeRow } from '../components/SwipeRow';
 import type { RootStackParamList } from '../navigation/types';
-import { performAppCheckIn } from '../offline/checkInService';
+import { performAppCheckIn, performAppUndoCheckIn } from '../offline/checkInService';
 import { useOffline } from '../offline/OfflineContext';
+import { formatSyncAlert } from '../offline/syncEngine';
 import {
   countPendingForSession,
   isOfflinePackActive,
@@ -51,18 +54,41 @@ function formatCheckInTime(iso?: string | null) {
   return d.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit', hour12: true });
 }
 
+function formatLastSynced(iso?: string | null) {
+  if (!iso) return 'not yet';
+  const d = new Date(iso);
+  if (Number.isNaN(d.getTime())) return 'not yet';
+  return d.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' });
+}
+
 function ParticipantsHeader({
   eventName,
   sessionName,
   checkedInCount,
   totalCount,
+  onlyCheckedIn,
+  onToggleCheckedIn,
   onBack,
+  onSync,
+  syncing,
+  pendingCount,
+  isOnline,
+  offlineReady,
+  lastSyncedAt,
 }: {
   eventName: string;
   sessionName: string;
   checkedInCount: number;
   totalCount: number;
+  onlyCheckedIn: boolean;
+  onToggleCheckedIn: () => void;
   onBack: () => void;
+  onSync: () => void;
+  syncing: boolean;
+  pendingCount: number;
+  isOnline: boolean;
+  offlineReady: boolean;
+  lastSyncedAt: string | null;
 }) {
   const insets = useSafeAreaInsets();
 
@@ -71,12 +97,31 @@ function ParticipantsHeader({
       <View style={styles.headerBg} />
       <View style={styles.headerCircle} />
 
-      <Pressable onPress={onBack} hitSlop={10} style={styles.backBtn}>
-        <AppIcon name="arrow-back" size={18} color="rgba(255,255,255,0.85)" />
-        <Text style={styles.backLabel} numberOfLines={1}>
-          {eventName}
-        </Text>
-      </Pressable>
+      <View style={styles.headerTopRow}>
+        <Pressable onPress={onBack} hitSlop={10} style={styles.backBtn}>
+          <AppIcon name="arrow-back" size={18} color="rgba(255,255,255,0.85)" />
+          <Text style={styles.backLabel} numberOfLines={1}>
+            {eventName}
+          </Text>
+        </Pressable>
+        {offlineReady ? (
+          <Pressable
+            onPress={onSync}
+            hitSlop={10}
+            style={styles.syncBtn}
+            disabled={syncing || !isOnline}
+          >
+            {syncing ? (
+              <ActivityIndicator color="#fff" size="small" />
+            ) : (
+              <AppIcon name="cloud-upload-outline" size={16} color="#fff" />
+            )}
+            <Text style={styles.syncText}>
+              Sync{pendingCount > 0 ? ` (${pendingCount})` : ''}
+            </Text>
+          </Pressable>
+        ) : null}
+      </View>
 
       <View style={styles.headerMain}>
         <View style={styles.headerTextCol}>
@@ -84,13 +129,29 @@ function ParticipantsHeader({
             {sessionName}
           </Text>
           <Text style={styles.headerSubtitle}>
-            Attendance · {checkedInCount}/{totalCount} checked in
+            {offlineReady
+              ? `Offline mode · last synced ${formatLastSynced(lastSyncedAt)}`
+              : `Attendance · ${checkedInCount}/${totalCount} checked in`}
           </Text>
         </View>
-        <View style={styles.checkedBadge}>
-          <Text style={styles.checkedBadgeCount}>{checkedInCount}</Text>
-          <Text style={styles.checkedBadgeLabel}>checked in</Text>
-        </View>
+        <Pressable
+          onPress={onToggleCheckedIn}
+          accessibilityRole="button"
+          accessibilityState={{ selected: onlyCheckedIn }}
+          accessibilityLabel="Show only checked-in participants"
+          style={[styles.checkedBadge, onlyCheckedIn ? styles.checkedBadgeActive : null]}
+        >
+          <Text
+            style={[styles.checkedBadgeCount, onlyCheckedIn ? styles.checkedBadgeCountActive : null]}
+          >
+            {checkedInCount}
+          </Text>
+          <Text
+            style={[styles.checkedBadgeLabel, onlyCheckedIn ? styles.checkedBadgeLabelActive : null]}
+          >
+            checked in
+          </Text>
+        </Pressable>
       </View>
     </View>
   );
@@ -127,9 +188,10 @@ function SearchBar({
 }
 
 export function ParticipantsScreen({ navigation, route }: Props) {
-  const { eventId, eventName, attendanceId, attendanceName, allowDuplicate } = route.params;
+  const { eventId, eventName, attendanceId, attendanceName, allowDuplicate, allowAssignBlank } =
+    route.params;
   const insets = useSafeAreaInsets();
-  const { isOnline, refreshStatuses } = useOffline();
+  const { isOnline, syncing, statusByEvent, refreshStatuses, syncNow } = useOffline();
   const [all, setAll] = useState<AttendanceSearchParticipant[]>([]);
   const [searchQ, setSearchQ] = useState('');
   const [loading, setLoading] = useState(true);
@@ -139,15 +201,26 @@ export function ParticipantsScreen({ navigation, route }: Props) {
   const [resultError, setResultError] = useState<string | null>(null);
   const [pendingSync, setPendingSync] = useState(false);
   const [modalVisible, setModalVisible] = useState(false);
+  const [undoLoading, setUndoLoading] = useState(false);
+  const [openSwipeId, setOpenSwipeId] = useState<string | null>(null);
   const [fromCache, setFromCache] = useState(false);
+  const [sessionPending, setSessionPending] = useState(0);
+  const [onlyCheckedIn, setOnlyCheckedIn] = useState(false);
+
+  const status = statusByEvent[eventId];
+  const offlineReady = Boolean(status?.enabled);
+
+  useLayoutEffect(() => {
+    navigation.setOptions({ gestureEnabled: openSwipeId == null });
+  }, [navigation, openSwipeId]);
 
   const load = useCallback(async () => {
     setError(null);
     const packActive = await isOfflinePackActive(eventId);
     const pending = packActive ? await countPendingForSession(attendanceId) : 0;
+    setSessionPending(pending);
 
-    // Prefer local roster when offline, or when unsynced outbox would diverge from server.
-    if (packActive && (!isOnline || pending > 0)) {
+    if (packActive) {
       const local = await listOfflineParticipants(attendanceId);
       setAll(local);
       setFromCache(true);
@@ -161,12 +234,6 @@ export function ParticipantsScreen({ navigation, route }: Props) {
         setFromCache(false);
         return;
       }
-      if (packActive) {
-        const local = await listOfflineParticipants(attendanceId);
-        setAll(local);
-        setFromCache(true);
-        return;
-      }
       setError(res.error || 'Failed to load participants');
       setAll([]);
       setFromCache(false);
@@ -191,8 +258,11 @@ export function ParticipantsScreen({ navigation, route }: Props) {
   }, [navigation, load]);
 
   const displayed = useMemo(
-    () => all.filter((p) => matchesParticipant(p, searchQ)),
-    [all, searchQ],
+    () =>
+      all.filter(
+        (p) => (!onlyCheckedIn || p.alreadyCheckedIn) && matchesParticipant(p, searchQ),
+      ),
+    [all, searchQ, onlyCheckedIn],
   );
 
   const checkedInCount = useMemo(
@@ -225,13 +295,73 @@ export function ParticipantsScreen({ navigation, route }: Props) {
     await refreshStatuses();
   };
 
+  const handleSync = async () => {
+    const outcome = await syncNow({ eventId, attendanceId, pull: true });
+    await load();
+    Alert.alert('Sync', formatSyncAlert(outcome));
+  };
+
   const closeModal = () => {
+    if (undoLoading) return;
     setModalVisible(false);
     setResult(null);
     setResultError(null);
     setPendingSync(false);
   };
 
+  const handleUndo = async () => {
+    if (!result) return;
+    setUndoLoading(true);
+    const outcome = await performAppUndoCheckIn({
+      eventId,
+      attendanceId,
+      attendanceName,
+      participantId: result.participantId,
+    });
+    setUndoLoading(false);
+    if (!outcome.ok) {
+      Alert.alert('Undo failed', outcome.error);
+      return;
+    }
+    setModalVisible(false);
+    setResult(null);
+    setResultError(null);
+    setPendingSync(false);
+    await load();
+    await refreshStatuses();
+  };
+
+  const undoFromList = async (item: AttendanceSearchParticipant) => {
+    setOpenSwipeId(null);
+    setBusyId(item._id);
+    const outcome = await performAppUndoCheckIn({
+      eventId,
+      attendanceId,
+      attendanceName,
+      participantId: item._id,
+    });
+    setBusyId(null);
+    if (!outcome.ok) {
+      Alert.alert('Undo failed', outcome.error);
+      return;
+    }
+    await load();
+    await refreshStatuses();
+  };
+
+  const confirmUncheck = (item: AttendanceSearchParticipant) => {
+    Alert.alert('Uncheck-in', `Remove last check-in for ${item.displayName}?`, [
+      { text: 'Cancel', style: 'cancel' },
+      {
+        text: 'Uncheck-in',
+        style: 'destructive',
+        onPress: () => {
+          void undoFromList(item);
+        },
+      },
+    ]);
+  };
+
   const listBottomPad = Math.max(insets.bottom, 16) + 88;
 
   const renderItem = ({ item }: { item: AttendanceSearchParticipant }) => {
@@ -241,65 +371,88 @@ export function ParticipantsScreen({ navigation, route }: Props) {
     const meta = [item.email, item.phone].filter(Boolean).join(' · ') || '—';
     const checkInTime = formatCheckInTime(item.lastCheckedInAt);
 
-    return (
-      <Card style={styles.rowCard} padded>
-        <View style={styles.row}>
-          <View
+    const rowInner = (
+      <View style={styles.row}>
+        <View
+          style={[
+            styles.avatar,
+            item.alreadyCheckedIn ? styles.avatarChecked : styles.avatarPending,
+          ]}
+        >
+          <Text
             style={[
-              styles.avatar,
-              item.alreadyCheckedIn ? styles.avatarChecked : styles.avatarPending,
+              styles.avatarText,
+              item.alreadyCheckedIn ? styles.avatarTextChecked : styles.avatarTextPending,
             ]}
           >
-            <Text
-              style={[
-                styles.avatarText,
-                item.alreadyCheckedIn ? styles.avatarTextChecked : styles.avatarTextPending,
-              ]}
-            >
-              {getInitial(item.displayName)}
-            </Text>
-          </View>
+            {getInitial(item.displayName)}
+          </Text>
+        </View>
 
-          <View style={styles.rowText}>
-            <Text style={styles.name} numberOfLines={1}>
-              {item.displayName}
-            </Text>
-            <Text style={styles.meta} numberOfLines={1}>
-              {meta}
-            </Text>
-            {item.alreadyCheckedIn ? (
-              <View style={styles.checkedRow}>
-                <AppIcon name="checkmark-circle-outline" size={11} color={CHECKIN_GREEN} />
-                <Text style={styles.checked}>
-                  Checked in{checkInTime ? ` · ${checkInTime}` : ''}
-                </Text>
-              </View>
-            ) : null}
-          </View>
-
-          {showAction ? (
-            <Pressable
-              style={[
-                styles.checkBtn,
-                isAgain ? styles.checkBtnAgain : styles.checkBtnPrimary,
-              ]}
-              disabled={busyId === item._id}
-              onPress={() => checkIn(item._id)}
-            >
-              {busyId === item._id ? (
-                <ActivityIndicator color="#fff" size="small" />
-              ) : isAgain ? (
-                <View style={styles.checkBtnInner}>
-                  <AppIcon name="refresh-outline" size={11} color="#fff" />
-                  <Text style={styles.checkBtnText}>Again</Text>
-                </View>
-              ) : (
-                <Text style={styles.checkBtnText}>Check In</Text>
-              )}
-            </Pressable>
+        <View style={styles.rowText}>
+          <Text style={styles.name} numberOfLines={1}>
+            {item.displayName}
+          </Text>
+          <Text style={styles.meta} numberOfLines={1}>
+            {meta}
+          </Text>
+          {item.alreadyCheckedIn ? (
+            <View style={styles.checkedRow}>
+              <AppIcon name="checkmark-circle-outline" size={11} color={CHECKIN_GREEN} />
+              <Text style={styles.checked}>
+                Checked in{checkInTime ? ` · ${checkInTime}` : ''}
+              </Text>
+            </View>
           ) : null}
         </View>
-      </Card>
+
+        {showAction ? (
+          <Pressable
+            style={[
+              styles.checkBtn,
+              isAgain ? styles.checkBtnAgain : styles.checkBtnPrimary,
+            ]}
+            disabled={busyId === item._id}
+            onPress={() => checkIn(item._id)}
+          >
+            {busyId === item._id ? (
+              <ActivityIndicator color="#fff" size="small" />
+            ) : isAgain ? (
+              <View style={styles.checkBtnInner}>
+                <AppIcon name="refresh-outline" size={11} color="#fff" />
+                <Text style={styles.checkBtnText}>Again</Text>
+              </View>
+            ) : (
+              <Text style={styles.checkBtnText}>Check In</Text>
+            )}
+          </Pressable>
+        ) : null}
+      </View>
+    );
+
+    if (!item.alreadyCheckedIn) {
+      return (
+        <Card style={styles.rowCard} padded>
+          {rowInner}
+        </Card>
+      );
+    }
+
+    return (
+      <SwipeRow
+        enabled
+        open={openSwipeId === item._id}
+        onOpen={() => setOpenSwipeId(item._id)}
+        onClose={() => setOpenSwipeId((id) => (id === item._id ? null : id))}
+        actionLabel="Uncheck-in"
+        actionBusy={busyId === item._id}
+        onActionPress={() => confirmUncheck(item)}
+        style={styles.swipeRow}
+      >
+        <Card style={styles.swipeCard} padded>
+          {rowInner}
+        </Card>
+      </SwipeRow>
     );
   };
 
@@ -310,7 +463,17 @@ export function ParticipantsScreen({ navigation, route }: Props) {
         sessionName={attendanceName}
         checkedInCount={checkedInCount}
         totalCount={all.length}
+        onlyCheckedIn={onlyCheckedIn}
+        onToggleCheckedIn={() => setOnlyCheckedIn((v) => !v)}
         onBack={() => navigation.goBack()}
+        onSync={() => {
+          handleSync();
+        }}
+        syncing={syncing}
+        pendingCount={sessionPending}
+        isOnline={isOnline}
+        offlineReady={offlineReady}
+        lastSyncedAt={status?.lastSyncedAt ?? null}
       />
 
       <SearchBar value={searchQ} onChangeText={setSearchQ} />
@@ -326,6 +489,25 @@ export function ParticipantsScreen({ navigation, route }: Props) {
         <Text style={styles.countText}>
           {displayed.length} participant{displayed.length === 1 ? '' : 's'}
         </Text>
+        {allowAssignBlank ? (
+          <Pressable
+            style={styles.assignBtn}
+            onPress={() =>
+              navigation.navigate('QrScanner', {
+                eventId,
+                eventName,
+                attendanceId,
+                attendanceName,
+                allowDuplicate,
+                allowAssignBlank: true,
+                mode: 'assignBlank',
+              })
+            }
+          >
+            <AppIcon name="person-add-outline" size={14} color="#fff" />
+            <Text style={styles.assignBtnText}>Assign a Blank</Text>
+          </Pressable>
+        ) : null}
       </View>
 
       {loading ? (
@@ -355,9 +537,12 @@ export function ParticipantsScreen({ navigation, route }: Props) {
         onPress={() =>
           navigation.navigate('QrScanner', {
             eventId,
+            eventName,
             attendanceId,
             attendanceName,
             allowDuplicate,
+            allowAssignBlank: Boolean(allowAssignBlank),
+            mode: 'checkIn',
           })
         }
       >
@@ -371,6 +556,8 @@ export function ParticipantsScreen({ navigation, route }: Props) {
         error={resultError}
         pendingSync={pendingSync}
         onClose={closeModal}
+        onUndo={result ? handleUndo : undefined}
+        undoLoading={undoLoading}
       />
     </View>
   );
@@ -398,14 +585,35 @@ const styles = StyleSheet.create({
     backgroundColor: 'rgba(255,255,255,0.10)',
     zIndex: 0,
   },
+  headerTopRow: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    justifyContent: 'space-between',
+    marginBottom: spacing.md,
+    zIndex: 1,
+  },
   backBtn: {
     flexDirection: 'row',
     alignItems: 'center',
     gap: 8,
-    marginBottom: spacing.md,
     alignSelf: 'flex-start',
-    maxWidth: '85%',
-    zIndex: 1,
+    flex: 1,
+    minWidth: 0,
+    marginRight: 12,
+  },
+  syncBtn: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    gap: 6,
+    backgroundColor: 'rgba(255,255,255,0.18)',
+    paddingHorizontal: 12,
+    paddingVertical: 7,
+    borderRadius: radii.pill,
+  },
+  syncText: {
+    color: '#fff',
+    fontSize: 12,
+    fontWeight: '600',
   },
   backLabel: {
     color: 'rgba(255,255,255,0.85)',
@@ -438,6 +646,17 @@ const styles = StyleSheet.create({
     paddingVertical: 8,
     alignItems: 'center',
     minWidth: 64,
+    borderWidth: 1.5,
+    borderColor: 'transparent',
+  },
+  checkedBadgeActive: {
+    backgroundColor: '#fff',
+    borderColor: '#fff',
+    shadowColor: '#fff',
+    shadowOffset: { width: 0, height: 0 },
+    shadowOpacity: 1,
+    shadowRadius: 14,
+    elevation: 14,
   },
   checkedBadgeCount: {
     color: '#fff',
@@ -445,10 +664,16 @@ const styles = StyleSheet.create({
     fontWeight: '700',
     lineHeight: 24,
   },
+  checkedBadgeCountActive: {
+    color: colors.primaryDark,
+  },
   checkedBadgeLabel: {
     color: 'rgba(255,255,255,0.95)',
     fontSize: 11,
   },
+  checkedBadgeLabelActive: {
+    color: colors.primaryDark,
+  },
   cacheBanner: {
     flexDirection: 'row',
     alignItems: 'center',
@@ -487,16 +712,35 @@ const styles = StyleSheet.create({
     paddingVertical: 0,
   },
   countStrip: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    justifyContent: 'space-between',
+    gap: 12,
     backgroundColor: '#fff',
     paddingHorizontal: spacing.lg,
-    paddingVertical: 10,
+    paddingVertical: 8,
     borderBottomWidth: 1,
     borderBottomColor: '#F3F4F6',
   },
   countText: {
+    flex: 1,
     fontSize: 12,
     color: colors.muted,
   },
+  assignBtn: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    gap: 6,
+    backgroundColor: colors.primaryDark,
+    borderRadius: 12,
+    paddingHorizontal: 12,
+    paddingVertical: 7,
+  },
+  assignBtnText: {
+    color: '#fff',
+    fontSize: 12,
+    fontWeight: '700',
+  },
   list: {
     paddingHorizontal: spacing.lg,
     paddingTop: spacing.md,
@@ -513,6 +757,14 @@ const styles = StyleSheet.create({
     borderRadius: radii.xl,
     borderWidth: 0,
   },
+  swipeRow: {
+    marginBottom: 10,
+  },
+  swipeCard: {
+    marginBottom: 0,
+    borderRadius: radii.xl,
+    borderWidth: 0,
+  },
   row: {
     flexDirection: 'row',
     alignItems: 'center',
diff --git a/src/screens/QrScannerScreen.tsx b/src/screens/QrScannerScreen.tsx
index f70b66c..9ccd3ad 100644
--- a/src/screens/QrScannerScreen.tsx
+++ b/src/screens/QrScannerScreen.tsx
@@ -1,6 +1,7 @@
 import React, { useCallback, useRef, useState } from 'react';
 import {
   ActivityIndicator,
+  Alert,
   Pressable,
   StyleSheet,
   Text,
@@ -15,11 +16,13 @@ import {
   useCameraPermission,
   useCodeScanner,
 } from 'react-native-vision-camera';
+import { attendancesApi } from '../api/attendances';
 import type { AttendanceCheckInResult } from '../api/types';
 import { CheckInResultModal } from '../components/CheckInResultModal';
 import type { RootStackParamList } from '../navigation/types';
-import { performAppCheckIn } from '../offline/checkInService';
+import { performAppCheckIn, performAppUndoCheckIn } from '../offline/checkInService';
 import { useOffline } from '../offline/OfflineContext';
+import { getOfflineParticipant, isOfflinePackActive } from '../offline/repos';
 import { parseParticipantIdFromQr } from '../utils/parseParticipantQr';
 import { colors, radii, spacing, typography } from '../theme';
 import { PrimaryButton } from '../components/ui';
@@ -112,7 +115,8 @@ export function QrScannerScreen({ navigation, route }: Props) {
   const headerTop = insets.top + spacing.md;
   const [headerBottom, setHeaderBottom] = useState(headerTop + 96);
   const scanTop = headerBottom + SCAN_GAP_BELOW_HEADER;
-  const { eventId, attendanceId, attendanceName } = route.params;
+  const { eventId, eventName, attendanceId, attendanceName, mode = 'checkIn' } = route.params;
+  const assignBlank = mode === 'assignBlank';
   const { refreshStatuses } = useOffline();
   const { hasPermission, requestPermission } = useCameraPermission();
   const device = useCameraDevice('back');
@@ -122,6 +126,30 @@ export function QrScannerScreen({ navigation, route }: Props) {
   const [resultError, setResultError] = useState<string | null>(null);
   const [pendingSync, setPendingSync] = useState(false);
   const [modalVisible, setModalVisible] = useState(false);
+  const [undoLoading, setUndoLoading] = useState(false);
+
+  const goToAssignForm = useCallback(
+    (draft: {
+      participantId: string;
+      firstName?: string;
+      lastName?: string;
+      email?: string;
+      phone?: string;
+    }) => {
+      navigation.replace('AssignBlank', {
+        eventId,
+        eventName,
+        attendanceId,
+        attendanceName,
+        participantId: draft.participantId,
+        firstName: draft.firstName,
+        lastName: draft.lastName,
+        email: draft.email,
+        phone: draft.phone,
+      });
+    },
+    [navigation, eventId, eventName, attendanceId, attendanceName],
+  );
 
   const handleScan = useCallback(
     async (raw: string) => {
@@ -141,6 +169,82 @@ export function QrScannerScreen({ navigation, route }: Props) {
       setResultError(null);
       setPendingSync(false);
 
+      if (assignBlank) {
+        const packActive = await isOfflinePackActive(eventId);
+        let firstName = '';
+        let lastName = '';
+        let email = '';
+        let phone = '';
+        let found = false;
+
+        if (packActive) {
+          const local = await getOfflineParticipant(attendanceId, parsed.participantId);
+          if (local) {
+            found = true;
+            firstName = local.firstName || '';
+            lastName = local.lastName || '';
+            email = local.email || '';
+            phone = local.phone || '';
+          }
+        } else {
+          const preview = await attendancesApi.getParticipantPreview(
+            eventId,
+            attendanceId,
+            parsed.participantId,
+          );
+          if (!preview.error && preview.data) {
+            found = true;
+            firstName = preview.data.firstName || '';
+            lastName = preview.data.lastName || '';
+            email = preview.data.email || '';
+            phone = preview.data.phone || '';
+          }
+        }
+
+        setProcessing(false);
+        if (!found) {
+          setResult(null);
+          setResultError(
+            packActive
+              ? 'Participant not in offline pack. Refresh offline data while online.'
+              : 'Participant not in this attendance list.',
+          );
+          setModalVisible(true);
+          return;
+        }
+
+        const openForm = () =>
+          goToAssignForm({
+            participantId: parsed.participantId,
+            firstName,
+            lastName,
+            email,
+            phone,
+          });
+
+        if (firstName.trim() || email.trim()) {
+          const label = [firstName, lastName].filter(Boolean).join(' ').trim() || email;
+          Alert.alert(
+            'This badge already has details',
+            `${label} is already named. Assign this blank anyway?`,
+            [
+              {
+                text: 'Cancel',
+                style: 'cancel',
+                onPress: () => {
+                  scannedRef.current = false;
+                },
+              },
+              { text: 'Continue', onPress: openForm },
+            ],
+          );
+          return;
+        }
+
+        openForm();
+        return;
+      }
+
       const outcome = await performAppCheckIn({
         eventId,
         attendanceId,
@@ -161,7 +265,15 @@ export function QrScannerScreen({ navigation, route }: Props) {
       }
       setModalVisible(true);
     },
-    [eventId, attendanceId, attendanceName, processing, refreshStatuses],
+    [
+      assignBlank,
+      eventId,
+      attendanceId,
+      attendanceName,
+      processing,
+      refreshStatuses,
+      goToAssignForm,
+    ],
   );
 
   const codeScanner = useCodeScanner({
@@ -173,6 +285,7 @@ export function QrScannerScreen({ navigation, route }: Props) {
   });
 
   const closeModal = () => {
+    if (undoLoading) return;
     setModalVisible(false);
     setResult(null);
     setResultError(null);
@@ -183,6 +296,28 @@ export function QrScannerScreen({ navigation, route }: Props) {
     }
   };
 
+  const handleUndo = async () => {
+    if (!result) return;
+    setUndoLoading(true);
+    const outcome = await performAppUndoCheckIn({
+      eventId,
+      attendanceId,
+      attendanceName,
+      participantId: result.participantId,
+    });
+    setUndoLoading(false);
+    if (!outcome.ok) {
+      Alert.alert('Undo failed', outcome.error);
+      return;
+    }
+    setModalVisible(false);
+    setResult(null);
+    setResultError(null);
+    setPendingSync(false);
+    scannedRef.current = false;
+    refreshStatuses().catch(() => undefined);
+  };
+
   if (!hasPermission) {
     return (
       <View style={styles.centered}>
@@ -234,7 +369,9 @@ export function QrScannerScreen({ navigation, route }: Props) {
           }}
         >
           <Text style={styles.title}>{attendanceName}</Text>
-          <Text style={styles.hint}>Point at participant badge QR</Text>
+          <Text style={styles.hint}>
+            {assignBlank ? 'Scan blank badge QR' : 'Point at participant badge QR'}
+          </Text>
           {processing ? (
             <ActivityIndicator color="#fff" size="large" style={styles.spinner} />
           ) : null}
@@ -252,6 +389,8 @@ export function QrScannerScreen({ navigation, route }: Props) {
         error={resultError}
         pendingSync={pendingSync}
         onClose={closeModal}
+        onUndo={result && !assignBlank ? handleUndo : undefined}
+        undoLoading={undoLoading}
       />
     </View>
   );