diff --git a/client/src/api/client.ts b/client/src/api/client.ts
index 2d8b6ae3..d66c2503 100644
--- a/client/src/api/client.ts
+++ b/client/src/api/client.ts
@@ -4,6 +4,9 @@ import {
   weatherResultSchema, type WeatherResult,
   inAppListResultSchema, type InAppListResult,
   unreadCountResultSchema, type UnreadCountResult,
+  channelTestResultSchema,
+  mapsSearchResultSchema, mapsAutocompleteResultSchema, mapsPlaceDetailsResultSchema,
+  mapsPlacePhotoResultSchema, mapsReverseResultSchema, mapsResolveUrlResultSchema,
   type NotificationRespondRequest,
   type SettingUpsertRequest, type SettingsBulkRequest,
   type JourneyCreateRequest, type JourneyAddTripRequest,
@@ -57,6 +60,23 @@ export function parseInDev<S extends z.ZodTypeAny>(schema: S, data: unknown, lab
   }
   return data as z.infer<S>
 }
+
+/**
+ * Same dev-only drift check as parseInDev, but passes the payload straight
+ * through with its original inferred type instead of the schema type. Use this
+ * for endpoints whose existing consumers rely on the loose `r.data` type — it
+ * adds the development contract-drift warning without retyping the public
+ * surface (so it can never break a consumer that worked before).
+ */
+function checkInDev<T>(schema: z.ZodTypeAny, data: T, label: string): T {
+  if (API_DEV) {
+    const result = schema.safeParse(data)
+    if (!result.success) {
+      console.warn(`[api] ${label}: response did not match the @trek/shared schema`, result.error.issues)
+    }
+  }
+  return data
+}
 const RATE_LIMIT_MESSAGES: Record<string, string> = {
   en:      'Too many attempts. Please try again later.',
   de:      'Zu viele Versuche. Bitte versuchen Sie es später erneut.',
@@ -507,13 +527,13 @@ export const journeyApi = {
 }
 
 export const mapsApi = {
-  search: (query: string, lang?: string) => apiClient.post(`/maps/search?lang=${lang || 'en'}`, { query }).then(r => r.data),
+  search: (query: string, lang?: string) => apiClient.post(`/maps/search?lang=${lang || 'en'}`, { query }).then(r => checkInDev(mapsSearchResultSchema, r.data, 'maps.search')),
   autocomplete: (input: string, lang?: string, locationBias?: { low: { lat: number; lng: number }; high: { lat: number; lng: number } }, signal?: AbortSignal) =>
-      apiClient.post('/maps/autocomplete', { input, lang, locationBias }, { signal }).then(r => r.data),
-  details: (placeId: string, lang?: string) => apiClient.get(`/maps/details/${encodeURIComponent(placeId)}`, { params: { lang } }).then(r => r.data),
-  placePhoto: (placeId: string, lat?: number, lng?: number, name?: string) => apiClient.get(`/maps/place-photo/${encodeURIComponent(placeId)}`, { params: { lat, lng, name } }).then(r => r.data),
-  reverse: (lat: number, lng: number, lang?: string) => apiClient.get('/maps/reverse', { params: { lat, lng, lang } }).then(r => r.data),
-  resolveUrl: (url: string) => apiClient.post('/maps/resolve-url', { url }).then(r => r.data),
+      apiClient.post('/maps/autocomplete', { input, lang, locationBias }, { signal }).then(r => checkInDev(mapsAutocompleteResultSchema, r.data, 'maps.autocomplete')),
+  details: (placeId: string, lang?: string) => apiClient.get(`/maps/details/${encodeURIComponent(placeId)}`, { params: { lang } }).then(r => checkInDev(mapsPlaceDetailsResultSchema, r.data, 'maps.details')),
+  placePhoto: (placeId: string, lat?: number, lng?: number, name?: string) => apiClient.get(`/maps/place-photo/${encodeURIComponent(placeId)}`, { params: { lat, lng, name } }).then(r => checkInDev(mapsPlacePhotoResultSchema, r.data, 'maps.placePhoto')),
+  reverse: (lat: number, lng: number, lang?: string) => apiClient.get('/maps/reverse', { params: { lat, lng, lang } }).then(r => checkInDev(mapsReverseResultSchema, r.data, 'maps.reverse')),
+  resolveUrl: (url: string) => apiClient.post('/maps/resolve-url', { url }).then(r => checkInDev(mapsResolveUrlResultSchema, r.data, 'maps.resolveUrl')),
 }
 
 export const airportsApi = {
@@ -651,9 +671,9 @@ export const shareApi = {
 export const notificationsApi = {
   getPreferences: () => apiClient.get('/notifications/preferences').then(r => r.data),
   updatePreferences: (prefs: Record<string, Record<string, boolean>>) => apiClient.put('/notifications/preferences', prefs).then(r => r.data),
-  testSmtp: (email?: string) => apiClient.post('/notifications/test-smtp', { email }).then(r => r.data),
-  testWebhook: (url?: string) => apiClient.post('/notifications/test-webhook', { url }).then(r => r.data),
-  testNtfy: (payload: { topic?: string; server?: string | null; token?: string | null }) => apiClient.post('/notifications/test-ntfy', payload).then(r => r.data),
+  testSmtp: (email?: string) => apiClient.post('/notifications/test-smtp', { email }).then(r => checkInDev(channelTestResultSchema, r.data, 'notifications.testSmtp')),
+  testWebhook: (url?: string) => apiClient.post('/notifications/test-webhook', { url }).then(r => checkInDev(channelTestResultSchema, r.data, 'notifications.testWebhook')),
+  testNtfy: (payload: { topic?: string; server?: string | null; token?: string | null }) => apiClient.post('/notifications/test-ntfy', payload).then(r => checkInDev(channelTestResultSchema, r.data, 'notifications.testNtfy')),
 }
 
 export const inAppNotificationsApi = {
diff --git a/client/src/store/notify.ts b/client/src/store/notify.ts
new file mode 100644
index 00000000..82938049
--- /dev/null
+++ b/client/src/store/notify.ts
@@ -0,0 +1,17 @@
+// Bridge for surfacing user-facing toasts from non-component code (Zustand
+// slices, store actions) where the `useToast` hook isn't available. Mirrors the
+// global `window.__addToast` channel that ToastContainer registers and that
+// SystemNoticeBanner already uses for the same reason.
+
+type NotifyType = 'success' | 'error' | 'warning' | 'info'
+
+/**
+ * Show a toast from outside the React tree. No-ops gracefully if the
+ * ToastContainer hasn't registered its handler yet (e.g. very early boot),
+ * so callers never have to guard for it.
+ */
+export function notify(message: string, type: NotifyType = 'info', duration?: number): void {
+  if (typeof window !== 'undefined' && typeof window.__addToast === 'function') {
+    window.__addToast(message, type, duration)
+  }
+}
diff --git a/client/src/store/slices/budgetSlice.ts b/client/src/store/slices/budgetSlice.ts
index b57c4fb9..40dd2189 100644
--- a/client/src/store/slices/budgetSlice.ts
+++ b/client/src/store/slices/budgetSlice.ts
@@ -5,6 +5,7 @@ import type { TripStoreState } from '../tripStore'
 import type { BudgetItem, BudgetItemMember } from '../../types'
 import type { BudgetCreateItemRequest, BudgetUpdateItemRequest } from '@trek/shared'
 import { getApiErrorMessage } from '../../types'
+import { notify } from '../notify'
 
 type SetState = StoreApi<TripStoreState>['setState']
 type GetState = StoreApi<TripStoreState>['getState']
@@ -104,10 +105,12 @@ export const createBudgetSlice = (set: SetState, get: GetState): BudgetSlice =>
     })
     try {
       await budgetApi.reorderItems(tripId, orderedIds)
-    } catch {
-      // Reload on failure
+    } catch (err: unknown) {
+      // Reload on failure to restore the server's ordering, and tell the user
+      // their reorder didn't stick (the caller fires this without awaiting).
       const data = await budgetApi.list(tripId)
       set({ budgetItems: data.items })
+      notify(getApiErrorMessage(err, 'Error reordering budget items'), 'error')
     }
   },
 
@@ -132,9 +135,12 @@ export const createBudgetSlice = (set: SetState, get: GetState): BudgetSlice =>
     })
     try {
       await budgetApi.reorderCategories(tripId, orderedCategories)
-    } catch {
+    } catch (err: unknown) {
+      // Reload on failure to restore the server's ordering, and tell the user
+      // their reorder didn't stick (the caller fires this without awaiting).
       const data = await budgetApi.list(tripId)
       set({ budgetItems: data.items })
+      notify(getApiErrorMessage(err, 'Error reordering budget items'), 'error')
     }
   },
 })
diff --git a/client/src/store/slices/packingSlice.ts b/client/src/store/slices/packingSlice.ts
index ab3f373b..2bd10957 100644
--- a/client/src/store/slices/packingSlice.ts
+++ b/client/src/store/slices/packingSlice.ts
@@ -3,6 +3,7 @@ import type { StoreApi } from 'zustand'
 import type { TripStoreState } from '../tripStore'
 import type { PackingItem } from '../../types'
 import { getApiErrorMessage } from '../../types'
+import { notify } from '../notify'
 
 type SetState = StoreApi<TripStoreState>['setState']
 type GetState = StoreApi<TripStoreState>['getState']
@@ -56,12 +57,15 @@ export const createPackingSlice = (set: SetState, get: GetState): PackingSlice =
     }))
     try {
       await packingRepo.update(tripId, id, { checked })
-    } catch {
+    } catch (err: unknown) {
+      // The caller fires this optimistically and doesn't await, so rolling back
+      // silently would just flip the checkbox with no explanation. Surface it.
       set(state => ({
         packingItems: state.packingItems.map(item =>
           item.id === id ? { ...item, checked: checked ? 0 : 1 } : item
         )
       }))
+      notify(getApiErrorMessage(err, 'Error updating item'), 'error')
     }
   },
 })
diff --git a/client/src/store/slices/reservationsSlice.ts b/client/src/store/slices/reservationsSlice.ts
index c020a593..96414c9a 100644
--- a/client/src/store/slices/reservationsSlice.ts
+++ b/client/src/store/slices/reservationsSlice.ts
@@ -58,8 +58,11 @@ export const createReservationsSlice = (set: SetState, get: GetState): Reservati
     }))
     try {
       await reservationsApi.update(tripId, id, { status: newStatus })
-    } catch {
+    } catch (err: unknown) {
+      // Roll back the optimistic toggle and surface the failure so the caller's
+      // catch can notify the user — without it the status silently snaps back.
       set({ reservations: prev })
+      throw new Error(getApiErrorMessage(err, 'Error updating reservation'))
     }
   },
 
diff --git a/client/src/store/slices/todoSlice.ts b/client/src/store/slices/todoSlice.ts
index 58070a85..ce545fa5 100644
--- a/client/src/store/slices/todoSlice.ts
+++ b/client/src/store/slices/todoSlice.ts
@@ -3,6 +3,7 @@ import type { StoreApi } from 'zustand'
 import type { TripStoreState } from '../tripStore'
 import type { TodoItem } from '../../types'
 import { getApiErrorMessage } from '../../types'
+import { notify } from '../notify'
 
 type SetState = StoreApi<TripStoreState>['setState']
 type GetState = StoreApi<TripStoreState>['getState']
@@ -56,12 +57,15 @@ export const createTodoSlice = (set: SetState, get: GetState): TodoSlice => ({
     }))
     try {
       await todoApi.update(tripId, id, { checked })
-    } catch {
+    } catch (err: unknown) {
+      // The caller fires this optimistically and doesn't await, so rolling back
+      // silently would just flip the checkbox with no explanation. Surface it.
       set(state => ({
         todoItems: state.todoItems.map(item =>
           item.id === id ? { ...item, checked: checked ? 0 : 1 } : item
         )
       }))
+      notify(getApiErrorMessage(err, 'Error updating todo'), 'error')
     }
   },
 })
diff --git a/client/tests/unit/slices/reservationsSlice.test.ts b/client/tests/unit/slices/reservationsSlice.test.ts
index eea9810d..a95b91b7 100644
--- a/client/tests/unit/slices/reservationsSlice.test.ts
+++ b/client/tests/unit/slices/reservationsSlice.test.ts
@@ -123,7 +123,7 @@ describe('reservationsSlice', () => {
       expect(useTripStore.getState().reservations[0].status).toBe('confirmed');
     });
 
-    it('FE-RESERV-007: toggleReservationStatus rolls back on API failure (silent)', async () => {
+    it('FE-RESERV-007: toggleReservationStatus rolls back and surfaces the error on API failure', async () => {
       const reservation = buildReservation({ id: 10, trip_id: 1, status: 'confirmed' });
       seedStore(useTripStore, { reservations: [reservation] });
 
@@ -133,8 +133,9 @@ describe('reservationsSlice', () => {
         ),
       );
 
-      // Does NOT throw (silent rollback)
-      await useTripStore.getState().toggleReservationStatus(1, 10);
+      // Rolls back the optimistic toggle AND rejects, so the caller's catch can
+      // show a toast (previously the failure was swallowed and the toast never fired).
+      await expect(useTripStore.getState().toggleReservationStatus(1, 10)).rejects.toThrow();
 
       expect(useTripStore.getState().reservations[0].status).toBe('confirmed');
     });