From af7dbce105be44a90bbabebf06e4813ff4909acb Mon Sep 17 00:00:00 2001
From: elmocito <42518790+elmocito@users.noreply.github.com>
Date: Mon, 5 Oct 2026 23:53:11 +0200
Subject: [PATCH] fix(tours): prevent duplicate day assignments

---
 .../components/Tours/ToursSidebar.test.tsx    |  30 +++++
 client/src/components/Tours/ToursSidebar.tsx  |   2 +-
 .../Tours/planner/TourPlannerPanels.tsx       |   2 +
 client/src/components/Tours/tourParts.tsx     |  19 ++-
 .../components/shared/ContextMenu.test.tsx    |   9 ++
 client/src/components/shared/ContextMenu.tsx  |   9 +-
 .../trip/sheets/MBrowseActionsSheet.tsx       |  19 ++-
 .../pages/tripPlanner/useTripPlanner.test.tsx |  31 +++++
 .../src/pages/tripPlanner/useTripPlanner.ts   |   1 +
 .../trip/MBrowseActionsSheet.tours.test.tsx   | 109 ++++++++++++++++++
 .../nest/assignments/assignments.service.ts   |  11 +-
 server/tests/e2e/assignments.e2e.test.ts      |  32 +++++
 .../unit/nest/assignments.controller.test.ts  |  14 ++-
 .../unit/nest/assignments.service.test.ts     |  40 +++++++
 14 files changed, 313 insertions(+), 15 deletions(-)
 create mode 100644 client/tests/unit/mobile/trip/MBrowseActionsSheet.tours.test.tsx

diff --git a/client/src/components/Tours/ToursSidebar.test.tsx b/client/src/components/Tours/ToursSidebar.test.tsx
index 0879cbf7e..cad5e72f9 100644
--- a/client/src/components/Tours/ToursSidebar.test.tsx
+++ b/client/src/components/Tours/ToursSidebar.test.tsx
@@ -129,6 +129,36 @@ describe('ToursSidebar', () => {
     expect(onToursChanged).not.toHaveBeenCalled()
   })
 
+  it('disables already-assigned days and refreshes availability when the picker is reopened', async () => {
+    const dayOne = { id: 7, trip_id: 1, day_number: 1, title: 'Day one', date: null } as never
+    const dayTwo = { id: 8, trip_id: 1, day_number: 2, title: 'Day two', date: null } as never
+    const dayThree = { id: 9, trip_id: 1, day_number: 3, title: 'Day three', date: null } as never
+    useTripStore.setState({ assignments: { '7': [{ id: 1, day_id: 7, place_id: tour.place_id }] } as never })
+    const onAssignToDay = vi.fn((placeId: number, dayId: number) => {
+      useTripStore.setState(state => ({
+        assignments: { ...state.assignments, [String(dayId)]: [{ id: 2, day_id: dayId, place_id: placeId }] } as never,
+      }))
+      return true
+    })
+    render(<ToursSidebar canAssign tripId={1} days={[dayOne, dayTwo, dayThree]} tours={[tour]} onAssignToDay={onAssignToDay} onSelectTour={vi.fn()} />)
+
+    const openPicker = () => fireEvent.click(screen.getByRole('button', { name: /Add to day|Zum Tag hinzufügen/ }))
+    openPicker()
+    expect(screen.getByRole('button', { name: /Day one/ })).toBeDisabled()
+    expect(screen.getByRole('button', { name: /Day two/ })).toBeEnabled()
+    fireEvent.click(screen.getByRole('button', { name: /Day two/ }))
+    expect(onAssignToDay).toHaveBeenCalledTimes(1)
+    expect(onAssignToDay).toHaveBeenCalledWith(tour.place_id, 8)
+
+    openPicker()
+    expect(screen.getByRole('button', { name: /Day one/ })).toBeDisabled()
+    expect(screen.getByRole('button', { name: /Day two/ })).toBeDisabled()
+    expect(screen.getByRole('button', { name: /Day three/ })).toBeEnabled()
+    fireEvent.click(screen.getByRole('button', { name: /Day three/ }))
+    expect(onAssignToDay).toHaveBeenCalledTimes(2)
+    expect(onAssignToDay).toHaveBeenLastCalledWith(tour.place_id, 9)
+  })
+
   it('neither refreshes nor reports success when assignment fails', async () => {
     toast.success.mockClear()
     const onToursChanged = vi.fn()
diff --git a/client/src/components/Tours/ToursSidebar.tsx b/client/src/components/Tours/ToursSidebar.tsx
index 4157efc02..f61b1a907 100644
--- a/client/src/components/Tours/ToursSidebar.tsx
+++ b/client/src/components/Tours/ToursSidebar.tsx
@@ -178,7 +178,7 @@ export default function ToursSidebar({ tripId, days, tours, loading = false, sel
                 tour={tour}
                 selected={tour.place_id === selectedPlaceId}
                 onSelect={(selectedTour, opener) => onSelectTour?.(selectedTour, opener)}
-                action={<TourDayMenu days={days} label={t('tours.addToDay')} disabled={!canAssign} onPick={(day, index) => { void handleAssign(tour, day, index) }} />}
+                action={<TourDayMenu days={days} placeId={tour.place_id} label={t('tours.addToDay')} disabled={!canAssign} onPick={(day, index) => { void handleAssign(tour, day, index) }} />}
               />
             ))}
           </ul>
diff --git a/client/src/components/Tours/planner/TourPlannerPanels.tsx b/client/src/components/Tours/planner/TourPlannerPanels.tsx
index 8f1cd1c78..82c0dde17 100644
--- a/client/src/components/Tours/planner/TourPlannerPanels.tsx
+++ b/client/src/components/Tours/planner/TourPlannerPanels.tsx
@@ -471,6 +471,7 @@ export function TourPlannerToursRail({ planner, tours, days, loading, onAssignTo
                 variant="button"
                 primary
                 days={days}
+                placeId={planner.saveOutcome.place_id}
                 label={t('tours.planner.assignToDay')}
                 disabled={!canAssign || assigning}
                 onPick={day => { void assignSavedTour(day.id) }}
@@ -498,6 +499,7 @@ export function TourPlannerToursRail({ planner, tours, days, loading, onAssignTo
                     action={canAssign && days.length > 0 ? (
                       <TourDayMenu
                         days={days}
+                        placeId={tour.place_id}
                         label={`${t('tours.addToDay')}: ${tour.name}`}
                         onPick={day => { if (canAssign) void onAssignToDay(tour.place_id, day.id) }}
                       />
diff --git a/client/src/components/Tours/tourParts.tsx b/client/src/components/Tours/tourParts.tsx
index 27376056c..2449f8eab 100644
--- a/client/src/components/Tours/tourParts.tsx
+++ b/client/src/components/Tours/tourParts.tsx
@@ -10,6 +10,7 @@ import { formatDate } from '../../utils/formatters'
 import { ContextMenu, useContextMenu } from '../shared/ContextMenu'
 import { DialogButton, fs } from '../shared/DialogShell'
 import { Tooltip } from '../shared/Tooltip'
+import { useTripStore } from '../../store/tripStore'
 import { BOX, Eyebrow } from '../Planner/bookings/bookingParts'
 import { SoftPill } from '../Planner/planParts'
 import { hikeSourceBadgeLabel } from './tourPresentation'
@@ -73,8 +74,9 @@ function dayMenuLabel(day: Day, index: number, t: Translate, locale: string): st
  * Putting a tour on a day: a round "+" on a row, or a footer button with a
  * chevron, both opening the trip's days as a menu.
  */
-export function TourDayMenu({ days, onPick, disabled = false, label, variant = 'round', primary = false }: {
+export function TourDayMenu({ days, placeId, onPick, disabled = false, label, variant = 'round', primary = false }: {
   days: Day[]
+  placeId?: number
   onPick: (day: Day, index: number) => void
   disabled?: boolean
   label: string
@@ -83,9 +85,16 @@ export function TourDayMenu({ days, onPick, disabled = false, label, variant = '
 }) {
   const { t, locale } = useTranslation()
   const menu = useContextMenu()
-  const items = days.map((day, index) => ({ label: dayMenuLabel(day, index, t, locale), onClick: () => onPick(day, index) }))
+  const assignments = useTripStore(state => state.assignments ?? {})
+  const assigned = (dayId: number) => placeId != null && (assignments[String(dayId)] ?? []).some(assignment => assignment.place_id === placeId)
+  const items = days.map((day, index) => ({
+    label: dayMenuLabel(day, index, t, locale),
+    disabled: assigned(day.id),
+    onClick: () => onPick(day, index),
+  }))
+  const hasAvailableDay = items.some(item => !item.disabled)
   const open = (event: React.MouseEvent<HTMLButtonElement>) => {
-    if (disabled || items.length === 0) return
+    if (disabled || !hasAvailableDay) return
     if (menu.menu) { event.stopPropagation(); menu.close(); return }
     menu.open(event, items, true)
   }
@@ -93,13 +102,13 @@ export function TourDayMenu({ days, onPick, disabled = false, label, variant = '
     <>
       {variant === 'round' ? (
         <Tooltip label={label} disabled={!!menu.menu}>
-          <button type="button" onClick={open} disabled={disabled || items.length === 0} aria-label={label} aria-haspopup="menu" aria-expanded={!!menu.menu}
+          <button type="button" onClick={open} disabled={disabled || !hasAvailableDay} aria-label={label} aria-haspopup="menu" aria-expanded={!!menu.menu}
             className={`grid h-[26px] w-[26px] flex-none place-items-center rounded-full shadow-sm ring-1 transition-colors disabled:cursor-default disabled:opacity-40 ${menu.menu ? 'bg-accent text-accent-text ring-transparent' : 'bg-surface-card text-content-muted ring-edge-faint enabled:hover:bg-accent enabled:hover:text-accent-text enabled:hover:ring-transparent'}`}>
             <Plus size={13} strokeWidth={2.4} />
           </button>
         </Tooltip>
       ) : (
-        <DialogButton variant={primary ? 'primary' : 'secondary'} onClick={open} disabled={disabled || items.length === 0}
+        <DialogButton variant={primary ? 'primary' : 'secondary'} onClick={open} disabled={disabled || !hasAvailableDay}
           aria-haspopup="menu" aria-expanded={!!menu.menu} icon={<Plus size={14} strokeWidth={2} />}>
           {label}
           <ChevronDown size={13} strokeWidth={2.2} className={`transition-transform ${menu.menu ? 'rotate-180' : ''}`} />
diff --git a/client/src/components/shared/ContextMenu.test.tsx b/client/src/components/shared/ContextMenu.test.tsx
index 5f00397f6..4838ac09a 100644
--- a/client/src/components/shared/ContextMenu.test.tsx
+++ b/client/src/components/shared/ContextMenu.test.tsx
@@ -79,4 +79,13 @@ describe('ContextMenu', () => {
     });
     expect(onClose).toHaveBeenCalledOnce();
   });
+
+  it('does not activate a disabled menu item', () => {
+    const onClick = vi.fn()
+    render(<ContextMenu menu={makeMenu(100, 200, [{ label: 'Already assigned', onClick, disabled: true }])} onClose={onClose} />)
+    const item = screen.getByRole('button', { name: 'Already assigned' })
+    expect(item).toBeDisabled()
+    fireEvent.click(item)
+    expect(onClick).not.toHaveBeenCalled()
+  })
 });
diff --git a/client/src/components/shared/ContextMenu.tsx b/client/src/components/shared/ContextMenu.tsx
index 3558a9398..6cdb6a22f 100644
--- a/client/src/components/shared/ContextMenu.tsx
+++ b/client/src/components/shared/ContextMenu.tsx
@@ -6,6 +6,7 @@ interface MenuItem {
   label?: string
   icon?: LucideIcon
   onClick?: () => void
+  disabled?: boolean
   danger?: boolean
   divider?: boolean
 }
@@ -84,15 +85,15 @@ export function ContextMenu({ menu, onClose }: ContextMenuProps) {
         if (item.divider) return <div key={i} style={{ height: 1, background: 'var(--border-faint)', margin: '3px 6px' }} />
         const Icon = item.icon
         return (
-          <button type="button" key={i} onClick={() => { item.onClick?.(); onClose() }} style={{
+          <button type="button" key={i} disabled={item.disabled} onClick={() => { if (item.disabled) return; item.onClick?.(); onClose() }} style={{
             display: 'flex', alignItems: 'center', gap: 8, width: '100%',
             padding: '7px 10px', borderRadius: 7, border: 'none',
-            background: 'none', cursor: 'pointer', fontFamily: 'inherit',
+            background: 'none', cursor: item.disabled ? 'default' : 'pointer', fontFamily: 'inherit',
             fontSize: 'calc(12px * var(--fs-scale-body, 1))', fontWeight: 500, textAlign: 'left',
-            color: item.danger ? '#ef4444' : 'var(--text-primary)',
+            color: item.danger ? '#ef4444' : 'var(--text-primary)', opacity: item.disabled ? 0.45 : 1,
             transition: 'background 0.1s',
           }}
-            onMouseEnter={e => e.currentTarget.style.background = item.danger ? 'rgba(239,68,68,0.08)' : 'var(--bg-hover)'}
+            onMouseEnter={e => { if (!item.disabled) e.currentTarget.style.background = item.danger ? 'rgba(239,68,68,0.08)' : 'var(--bg-hover)' }}
             onMouseLeave={e => e.currentTarget.style.background = 'none'}
           >
             {Icon && <Icon size={13} style={{ flexShrink: 0, color: item.danger ? '#ef4444' : 'var(--text-faint)' }} />}
diff --git a/client/src/mobile/screens/trip/sheets/MBrowseActionsSheet.tsx b/client/src/mobile/screens/trip/sheets/MBrowseActionsSheet.tsx
index f4d2317a6..18d5fae13 100644
--- a/client/src/mobile/screens/trip/sheets/MBrowseActionsSheet.tsx
+++ b/client/src/mobile/screens/trip/sheets/MBrowseActionsSheet.tsx
@@ -31,6 +31,7 @@ export default function MBrowseActionsSheet({ planner, shell }: MTripSheetsProps
   const openSavePicker = useSaveToCollectionStore(s => s.open)
 
   const [daysOpen, setDaysOpen] = useState(false)
+  const pendingTourDayIds = useRef(new Set<string>())
   useEffect(() => { setDaysOpen(open && Boolean(payload.dayPicker)) }, [open, payload.dayPicker])
 
   // Hold the last place so the card content survives the exit animation.
@@ -57,9 +58,20 @@ export default function MBrowseActionsSheet({ planner, shell }: MTripSheetsProps
     openSavePicker(collectionTargetFromPlace(place))
   }
 
+  const tourAlreadyAssignedToDay = (dayId: number) => isTourPlace(place.id)
+    && (planner.assignments[String(dayId)] ?? []).some(assignment => assignment.place_id === place.id)
+
   const assignToDay = async (dayId: number) => {
-    const assigned = await planner.handleAssignToDay(place.id, dayId)
-    if (assigned !== false) shell.closeSheet()
+    const isTour = isTourPlace(place.id)
+    const pendingKey = `${place.id}:${dayId}`
+    if (isTour && (tourAlreadyAssignedToDay(dayId) || pendingTourDayIds.current.has(pendingKey))) return
+    if (isTour) pendingTourDayIds.current.add(pendingKey)
+    try {
+      const assigned = await planner.handleAssignToDay(place.id, dayId)
+      if (assigned !== false) shell.closeSheet()
+    } finally {
+      if (isTour) pendingTourDayIds.current.delete(pendingKey)
+    }
   }
 
   const deletePlace = () => {
@@ -112,8 +124,9 @@ export default function MBrowseActionsSheet({ planner, shell }: MTripSheetsProps
                   <button
                     key={d.id}
                     type="button"
+                    disabled={tourAlreadyAssignedToDay(d.id) || (isTourPlace(place.id) && pendingTourDayIds.current.has(`${place.id}:${d.id}`))}
                     onClick={() => { void assignToDay(d.id) }}
-                    className={`flex w-full items-center gap-2 px-3 py-[10px] text-left ${i > 0 ? 'border-t border-[color:var(--m-rowbr)]' : ''}`}
+                    className={`flex w-full items-center gap-2 px-3 py-[10px] text-left disabled:cursor-default disabled:opacity-40 ${i > 0 ? 'border-t border-[color:var(--m-rowbr)]' : ''}`}
                   >
                     <span className="min-w-0 flex-1 truncate text-[0.78125rem] font-semibold">
                       {/* A day_number of 0 is as unusable as a missing one — both take the row position. */}
diff --git a/client/src/pages/tripPlanner/useTripPlanner.test.tsx b/client/src/pages/tripPlanner/useTripPlanner.test.tsx
index a8a4854e6..55e510c89 100644
--- a/client/src/pages/tripPlanner/useTripPlanner.test.tsx
+++ b/client/src/pages/tripPlanner/useTripPlanner.test.tsx
@@ -1567,6 +1567,37 @@ describe('useTripPlanner — place CRUD', () => {
 })
 
 describe('useTripPlanner — day plan CRUD', () => {
+  it('does not write a Tour assignment twice to one day, but allows another day and preserves Place writes', async () => {
+    const tour: TourListItem = {
+      place_id: 1, name: 'Ridge walk', tour_type: 'hike', distance: 4, elevation_gain: 100,
+      elevation_loss: 80, duration: null, difficulty: null, wanderer_ref: null, match_confidence: 1,
+      tour_group_id: null, max_hiking_difficulty: 2, planned: false, caution: false,
+    }
+    const tourPlace = buildPlace({ id: 1, name: 'Ridge walk', tour_place_id: 1 })
+    const ordinaryPlace = buildPlace({ id: 2, name: 'Ordinary place' })
+    useAddonStore.setState({ addons: [{ id: 'tours', enabled: true } as never], loaded: true })
+    vi.mocked(addonsApi.enabled).mockResolvedValue({ addons: [{ id: 'tours' }] })
+    vi.spyOn(toursApi, 'list').mockResolvedValue({ tours: [tour] })
+    seedTrip({
+      places: [tourPlace, ordinaryPlace],
+      assignments: { '7': [buildAssignment({ id: 70, day_id: 7, place: tourPlace })] },
+    })
+
+    const { result } = await renderPlanner()
+    await waitFor(() => expect(result.current.tours).toEqual([tour]))
+    actions.assignPlaceToDay.mockClear()
+
+    let repeated!: boolean
+    await act(async () => { repeated = await result.current.handleAssignToDay(tourPlace.id, 7) })
+    expect(repeated).toBe(false)
+    expect(actions.assignPlaceToDay).not.toHaveBeenCalled()
+
+    await act(async () => { await result.current.handleAssignToDay(tourPlace.id, 8) })
+    await act(async () => { await result.current.handleAssignToDay(ordinaryPlace.id, 7) })
+    expect(actions.assignPlaceToDay).toHaveBeenNthCalledWith(1, 42, 8, tourPlace.id, undefined)
+    expect(actions.assignPlaceToDay).toHaveBeenNthCalledWith(2, 42, 7, ordinaryPlace.id, undefined)
+  })
+
   it('refreshes Tours only after a successful Tour assignment write', async () => {
     const unplanned: TourListItem = {
       place_id: 1, name: 'Ridge walk', tour_type: 'hike', distance: 4, elevation_gain: 100,
diff --git a/client/src/pages/tripPlanner/useTripPlanner.ts b/client/src/pages/tripPlanner/useTripPlanner.ts
index 993ee1055..4dfd4e831 100644
--- a/client/src/pages/tripPlanner/useTripPlanner.ts
+++ b/client/src/pages/tripPlanner/useTripPlanner.ts
@@ -2527,6 +2527,7 @@ export function useTripPlanner() {
   const handleAssignToDay = useCallback(async (placeId: number, dayId?: number, position?: number) => {
     const target = dayId || selectedDayId
     if (!target) { toast.error(t('trip.toast.selectDay')); return false }
+    if (isTourPlace(placeId) && (storedAssignments[String(target)] ?? []).some(assignment => assignment.place_id === placeId)) return false
     const place = places.find(p => p.id === placeId)
     // A place with a start of its own is drawn by it, so it is stored there too, the
     // way a stop moved over from another day is. Without one it goes where it was put.
diff --git a/client/tests/unit/mobile/trip/MBrowseActionsSheet.tours.test.tsx b/client/tests/unit/mobile/trip/MBrowseActionsSheet.tours.test.tsx
new file mode 100644
index 000000000..7c20fea12
--- /dev/null
+++ b/client/tests/unit/mobile/trip/MBrowseActionsSheet.tours.test.tsx
@@ -0,0 +1,109 @@
+import { describe, expect, it, vi } from 'vitest';
+import type { TripPlanner } from '../../../../src/mobile/screens/trip/MTripShell';
+import MBrowseActionsSheet from '../../../../src/mobile/screens/trip/sheets/MBrowseActionsSheet';
+import type { Place } from '../../../../src/types';
+import { buildPlanner, buildShell } from '../../../helpers/mobileTrip';
+import { act, fireEvent, render, screen, waitFor } from '../../../helpers/render';
+import { resetAllStores } from '../../../helpers/store';
+
+function tourPlace(): Place {
+  return {
+    id: 42,
+    trip_id: 1,
+    name: 'Ridge walk',
+    address: null,
+    description: null,
+    category_id: null,
+    lat: 48,
+    lng: 11,
+    image_url: null,
+    google_place_id: null,
+    osm_id: null,
+    route_geometry: '[[48,11],[49,12]]',
+    route_color: null,
+    tour_place_id: 42,
+  } as unknown as Place;
+}
+
+const days = [
+  { id: 7, trip_id: 1, day_number: 1, title: 'Day one', date: null },
+  { id: 8, trip_id: 1, day_number: 2, title: 'Day two', date: null },
+  { id: 9, trip_id: 1, day_number: 3, title: 'Day three', date: null },
+] as never;
+
+function mobilePlanner(overrides: Partial<TripPlanner> = {}) {
+  const place = tourPlace();
+  return buildPlanner({
+    places: [place],
+    days,
+    assignments: { '7': [{ id: 70, day_id: 7, place_id: place.id }] } as never,
+    isTourPlace: vi.fn((placeId: number) => placeId === place.id),
+    ...overrides,
+  } as Partial<TripPlanner>);
+}
+
+function renderDayPicker(planner = mobilePlanner()) {
+  const shell = buildShell({ sheet: { id: 'bract', payload: { placeId: 42, dayPicker: true } } });
+  const view = render(<MBrowseActionsSheet planner={planner} shell={shell} />);
+  return { ...view, planner, shell };
+}
+
+describe('MBrowseActionsSheet Tour assignment picker', () => {
+  it('disables assigned Tour days, blocks repeat clicks, and refreshes on reopen', async () => {
+    resetAllStores();
+    let finishAssignment!: (assigned: boolean) => void;
+    const handleAssignToDay = vi.fn(
+      () =>
+        new Promise<boolean>((resolve) => {
+          finishAssignment = resolve;
+        })
+    );
+    const planner = mobilePlanner({ handleAssignToDay });
+    const { rerender, shell } = renderDayPicker(planner);
+
+    const dayOne = screen.getByRole('button', { name: /Day one/ });
+    const dayTwo = screen.getByRole('button', { name: /Day two/ });
+    expect(dayOne).toBeDisabled();
+    expect(dayTwo).toBeEnabled();
+    fireEvent.click(dayOne);
+    expect(handleAssignToDay).not.toHaveBeenCalled();
+
+    fireEvent.click(dayTwo);
+    fireEvent.click(dayTwo);
+    expect(handleAssignToDay).toHaveBeenCalledTimes(1);
+    expect(handleAssignToDay).toHaveBeenCalledWith(42, 8);
+
+    await act(async () => {
+      finishAssignment(true);
+    });
+    await waitFor(() => expect(shell.closeSheet).toHaveBeenCalledOnce());
+
+    const reopened = mobilePlanner({
+      assignments: {
+        '7': [{ id: 70, day_id: 7, place_id: 42 }],
+        '8': [{ id: 80, day_id: 8, place_id: 42 }],
+      } as never,
+    });
+    rerender(<MBrowseActionsSheet planner={reopened} shell={shell} />);
+    expect(screen.getByRole('button', { name: /Day one/ })).toBeDisabled();
+    expect(screen.getByRole('button', { name: /Day two/ })).toBeDisabled();
+    expect(screen.getByRole('button', { name: /Day three/ })).toBeEnabled();
+  });
+
+  it('leaves ordinary Place day choices enabled and preserves their assignment write behavior', () => {
+    resetAllStores();
+    const place = { ...tourPlace(), tour_place_id: undefined };
+    const handleAssignToDay = vi.fn().mockResolvedValue(true);
+    const planner = mobilePlanner({
+      places: [place],
+      isTourPlace: vi.fn(() => false),
+      assignments: { '7': [{ id: 70, day_id: 7, place_id: place.id }] } as never,
+      handleAssignToDay,
+    });
+    renderDayPicker(planner);
+    const dayOne = screen.getByRole('button', { name: /Day one/ });
+    expect(dayOne).toBeEnabled();
+    fireEvent.click(dayOne);
+    expect(handleAssignToDay).toHaveBeenCalledWith(place.id, 7);
+  });
+});
diff --git a/server/src/nest/assignments/assignments.service.ts b/server/src/nest/assignments/assignments.service.ts
index 3cf70583a..e8fbb13d9 100644
--- a/server/src/nest/assignments/assignments.service.ts
+++ b/server/src/nest/assignments/assignments.service.ts
@@ -1,4 +1,4 @@
-import { Injectable } from '@nestjs/common';
+import { ConflictException, Injectable } from '@nestjs/common';
 import { chronoOrder, type RoadtripVia, type TrekWsPayload, type TrekWsTripEventName } from '@trek/shared';
 import { isEmptyReanchoring, reanchorByStopOrder, type AnchoredVia } from '@trek/shared/roadtrip';
 import { RealtimeService } from '../realtime/realtime.service';
@@ -176,6 +176,15 @@ export class AssignmentsService {
    */
   createAssignment(dayId: string | number, placeId: unknown, notes?: string | null, opts: { accommodationId?: number; orderIndex?: number } = {}) {
     const result = this.dbs.transaction(() => {
+      const duplicateTourAssignment = this.dbs.get<{ id: number }>(
+        `SELECT da.id FROM day_assignments da
+         JOIN tours t ON t.place_id = da.place_id
+         WHERE da.day_id = ? AND da.place_id = ?
+         LIMIT 1`,
+        dayId, placeId,
+      );
+      if (duplicateTourAssignment) throw new ConflictException('Tour is already assigned to this day');
+
       const maxOrder = this.dbs.get<{ max: number | null }>('SELECT MAX(order_index) as max FROM day_assignments WHERE day_id = ?', dayId)!;
       const end = (maxOrder.max !== null ? maxOrder.max : -1) + 1;
       // Somewhere in the middle when the caller says so, which means everything from
diff --git a/server/tests/e2e/assignments.e2e.test.ts b/server/tests/e2e/assignments.e2e.test.ts
index ada4ee0cb..902768d3c 100644
--- a/server/tests/e2e/assignments.e2e.test.ts
+++ b/server/tests/e2e/assignments.e2e.test.ts
@@ -204,6 +204,38 @@ describe('Assignments e2e (real auth guard + temp SQLite)', () => {
     expect(miss.body).toEqual({ error: 'Place not found' });
   });
 
+  it('prevents duplicate Tour/day assignments through concurrent REST requests', async () => {
+    const tourPlaceId = 20;
+    db.prepare('INSERT INTO places (id, trip_id, name) VALUES (?, 5, ?)').run(tourPlaceId, 'Ridge walk');
+    db.prepare('INSERT INTO tours (place_id) VALUES (?)').run(tourPlaceId);
+    try {
+      const createTourAssignment = () => request(server)
+        .post('/api/trips/5/days/3/assignments')
+        .set('Cookie', sessionCookie(1))
+        .send({ place_id: tourPlaceId });
+      const results = await Promise.all([createTourAssignment(), createTourAssignment()]);
+
+      expect(results.map(result => result.status).sort()).toEqual([201, 409]);
+      expect(db.prepare('SELECT COUNT(*) AS n FROM day_assignments WHERE day_id = 3 AND place_id = ?').get(tourPlaceId)).toEqual({ n: 1 });
+
+      const otherDay = await request(server).post('/api/trips/5/days/4/assignments')
+        .set('Cookie', sessionCookie(1)).send({ place_id: tourPlaceId });
+      expect(otherDay.status).toBe(201);
+      expect(db.prepare('SELECT COUNT(*) AS n FROM day_assignments WHERE place_id = ?').get(tourPlaceId)).toEqual({ n: 2 });
+
+      const firstOrdinary = await request(server).post('/api/trips/5/days/3/assignments')
+        .set('Cookie', sessionCookie(1)).send({ place_id: 2 });
+      const secondOrdinary = await request(server).post('/api/trips/5/days/3/assignments')
+        .set('Cookie', sessionCookie(1)).send({ place_id: 2 });
+      expect(firstOrdinary.status).toBe(201);
+      expect(secondOrdinary.status).toBe(201);
+    } finally {
+      db.prepare('DELETE FROM day_assignments WHERE place_id = ?').run(tourPlaceId);
+      db.prepare('DELETE FROM tours WHERE place_id = ?').run(tourPlaceId);
+      db.prepare('DELETE FROM places WHERE id = ?').run(tourPlaceId);
+    }
+  });
+
   it('200 delete assignment reconciles journey skeletons', async () => {
     reconcileTripSkeletons.mockClear();
     const id = seedAssignment();
diff --git a/server/tests/unit/nest/assignments.controller.test.ts b/server/tests/unit/nest/assignments.controller.test.ts
index d868e7720..fd88a2f54 100644
--- a/server/tests/unit/nest/assignments.controller.test.ts
+++ b/server/tests/unit/nest/assignments.controller.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect, vi } from 'vitest';
-import { HttpException } from '@nestjs/common';
+import { ConflictException, HttpException } from '@nestjs/common';
 import { DayAssignmentsController, AssignmentOpsController } from '../../../src/nest/assignments/assignments.controller';
 import type { AssignmentsService } from '../../../src/nest/assignments/assignments.service';
 import type { User } from '../../../src/types';
@@ -47,6 +47,18 @@ describe('DayAssignmentsController (parity with the legacy day-assignments route
       expect(broadcast).toHaveBeenCalledWith('5', 'assignment:created', { assignment: { id: 9 } }, 'sock');
       expect(reconcile).toHaveBeenCalledWith('5', 'sock');
     });
+
+    it('409 duplicate Tour assignment propagates without announcing a new assignment', () => {
+      const broadcast = vi.fn();
+      const reconcile = vi.fn();
+      const createAssignment = vi.fn(() => { throw new ConflictException('Tour is already assigned to this day') });
+      const controller = new DayAssignmentsController(svc({ createAssignment, broadcast, reconcile } as Partial<AssignmentsService>));
+
+      expect(thrown(() => controller.create(user, '5', '3', { place_id: 42 }))).toMatchObject({ status: 409 });
+      expect(createAssignment).toHaveBeenCalledWith('3', 42, undefined);
+      expect(broadcast).not.toHaveBeenCalled();
+      expect(reconcile).not.toHaveBeenCalled();
+    });
   });
 
   it('PUT /reorder 404 day, else reorders + broadcasts', () => {
diff --git a/server/tests/unit/nest/assignments.service.test.ts b/server/tests/unit/nest/assignments.service.test.ts
index dbea060d5..f25f9b28a 100644
--- a/server/tests/unit/nest/assignments.service.test.ts
+++ b/server/tests/unit/nest/assignments.service.test.ts
@@ -10,6 +10,7 @@
  * logic is exercised faithfully.
  */
 import { describe, it, expect, vi, beforeAll, beforeEach, afterAll } from 'vitest';
+import { ConflictException } from '@nestjs/common';
 
 // ── DB setup ──────────────────────────────────────────────────────────────────
 
@@ -99,6 +100,11 @@ function fixture() {
   return { user, trip, day, place };
 }
 
+function addTourFacet(placeId: number) {
+  testDb.prepare("INSERT OR IGNORE INTO tour_types (key, label_key, icon, color) VALUES ('hike', 'hike', 'Mountain', '#000000')").run();
+  testDb.prepare("INSERT INTO tours (place_id, tour_type) VALUES (?, 'hike')").run(placeId);
+}
+
 // ── verifyTripAccess / canEdit ────────────────────────────────────────────────
 
 describe('verifyTripAccess', () => {
@@ -193,6 +199,40 @@ describe('createAssignment', () => {
     expect(a!.place.tags).toEqual([{ id: tag.id, name: 'museum', color: '#10b981', created_at: (tag as { created_at?: string }).created_at }]);
     void trip;
   });
+
+  it('ASG-SVC-031: rejects a duplicate Tour assignment on the same day but allows another day and ordinary Place duplicates', () => {
+    const { trip, day, place: tourPlace } = fixture();
+    const secondDay = createDay(testDb, trip.id);
+    const ordinaryPlace = createPlace(testDb, trip.id, { name: 'Ordinary place' });
+    addTourFacet(tourPlace.id);
+
+    const firstTourAssignment = svc.createAssignment(day.id, tourPlace.id);
+    expect(() => svc.createAssignment(day.id, tourPlace.id)).toThrow(ConflictException);
+    const otherDayTourAssignment = svc.createAssignment(secondDay.id, tourPlace.id);
+    expect(firstTourAssignment?.day_id).toBe(day.id);
+    expect(otherDayTourAssignment?.day_id).toBe(secondDay.id);
+    expect(testDb.prepare('SELECT COUNT(*) AS n FROM day_assignments WHERE place_id = ?').get(tourPlace.id)).toEqual({ n: 2 });
+
+    svc.createAssignment(day.id, ordinaryPlace.id);
+    svc.createAssignment(day.id, ordinaryPlace.id);
+    expect(testDb.prepare('SELECT COUNT(*) AS n FROM day_assignments WHERE place_id = ?').get(ordinaryPlace.id)).toEqual({ n: 2 });
+  });
+
+  it('ASG-SVC-032: near-concurrent Tour assignments serialize to one row and one conflict', async () => {
+    const { day, place } = fixture();
+    addTourFacet(place.id);
+
+    const results = await Promise.allSettled([
+      Promise.resolve().then(() => svc.createAssignment(day.id, place.id)),
+      Promise.resolve().then(() => svc.createAssignment(day.id, place.id)),
+    ]);
+
+    expect(results.filter(result => result.status === 'fulfilled')).toHaveLength(1);
+    const rejected = results.filter((result): result is PromiseRejectedResult => result.status === 'rejected');
+    expect(rejected).toHaveLength(1);
+    expect(rejected[0].reason).toBeInstanceOf(ConflictException);
+    expect(testDb.prepare('SELECT COUNT(*) AS n FROM day_assignments WHERE day_id = ? AND place_id = ?').get(day.id, place.id)).toEqual({ n: 1 });
+  });
 });
 
 // ── listDayAssignments ────────────────────────────────────────────────────────