feat(audit): undo button for merges, hide manual games

The audit log shows Undo on a merge row for 30 days, with a confirm
dialog and clear errors. The details page follows a merged key to the
kept game. Hide and Show now work for manual games too. de/en texts.

src/pages/AuditLogPage.jsx

@@ -1,17 +1,18 @@
 import {useCallback, useEffect, useState} from 'react';
 import {Link} from 'react-router-dom';
 import {useTranslation} from 'react-i18next';
-import {ChevronLeft, ChevronRight, Loader2} from 'lucide-react';
+import {ChevronLeft, ChevronRight, Loader2, Undo2} from 'lucide-react';
 
 import {Button} from '@/components/ui/button';
 import {Card, CardContent, CardHeader, CardTitle} from '@/components/ui/card';
 import {Select, SelectContent, SelectItem, SelectTrigger, SelectValue} from '@/components/ui/select';
 import PageContainer from '../components/PageContainer.jsx';
-import {fetchAuditLog} from '../utils/links.js';
+import {toast} from 'sonner';
+import {fetchAuditLog, undoMerge} from '../utils/links.js';
 import {formatDateTime} from '../utils/format.js';
 
 const PAGE_SIZE = 20;
-const ACTIONS = ['GAME_MERGE', 'GAME_LINK', 'GAME_UNLINK', 'GAME_LINK_DISMISS', 'GAME_CORRECT',
+const ACTIONS = ['GAME_MERGE', 'GAME_MERGE_UNDO', 'GAME_LINK', 'GAME_UNLINK', 'GAME_LINK_DISMISS', 'GAME_CORRECT',
     'GAME_CORRECTION_RESET'];
 const ALL = 'ALL';
 
@@ -29,6 +30,7 @@ export default function AuditLogPage() {
     const [page, setPage] = useState(0);
     const [result, setResult] = useState({content: [], totalPages: 0});
     const [status, setStatus] = useState('loading');
+    const [undoing, setUndoing] = useState(false);
 
     const load = useCallback(async () => {
         try {
@@ -54,6 +56,30 @@ export default function AuditLogPage() {
         load();
     }, [load]);
 
+    const onUndo = async (entry) => {
+        // The merged key has no catalog row any more; its name is the first one in the detail.
+        const name = entry.gameName ?? /^"(.*?)" into "/.exec(entry.detail ?? '')?.[1] ?? entry.appid;
+        const other = entry.targetGameName ?? entry.targetAppid;
+        if (!window.confirm(t('AUDIT.UNDO.CONFIRM', {name, other}))) return;
+        setUndoing(true);
+        try {
+            const response = await undoMerge(entry.id);
+            if (response.status === 401) return;
+            if (response.ok) {
+                toast.success(t('AUDIT.UNDO.DONE'));
+            } else {
+                const data = await response.json().catch(() => ({}));
+                toast.error(t(`AUDIT.UNDO.ERROR_CODES.${data.code}`, {defaultValue: t('AUDIT.UNDO.ERROR')}));
+            }
+            await load();
+        } catch (err) {
+            console.error('Undo merge error:', err);
+            toast.error(t('INFO.ERROR.NETWORK_FAILURE'));
+        } finally {
+            setUndoing(false);
+        }
+    };
+
     const onActionChange = (value) => {
         setAction(value);
         setPage(0);
@@ -100,6 +126,12 @@ export default function AuditLogPage() {
                                         <GameRef appid={entry.targetAppid} name={entry.targetGameName} fallback={entry.targetAppid}/>
                                     </p>
                                     {entry.detail && <p className="break-words text-xs text-muted-foreground">{entry.detail}</p>}
+                                    {entry.action === 'GAME_MERGE' && entry.undoable && (
+                                        <Button type="button" variant="outline" size="sm" disabled={undoing}
+                                                onClick={() => onUndo(entry)}>
+                                            <Undo2/>{t('AUDIT.UNDO.BUTTON')}
+                                        </Button>
+                                    )}
                                 </li>
                             ))}
                         </ul>

src/pages/AuditLogPage.test.jsx

@@ -5,16 +5,21 @@ import {MemoryRouter} from 'react-router-dom';
 import AuditLogPage from './AuditLogPage.jsx';
 import {PreferencesProvider} from '../context/PreferencesContext.jsx';
 import {fetchRoutes, json} from '../test/fetchRoutes.js';
+import {toast} from 'sonner';
 
 vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+vi.mock('sonner', () => ({toast: {success: vi.fn(), error: vi.fn()}}));
 
 const entry = (over) => ({id: 1, actorUserId: 5, actorName: 'lobo', action: 'GAME_LINK', appid: 10, gameName: 'Dark Souls',
     targetAppid: -7, targetGameName: 'Dark Souls Remastered', detail: '"Dark Souls" with "Dark Souls Remastered"',
     createdAt: '2026-10-01T10:00:00Z', ...over});
 const answer = (content, totalPages = 1) => json(200, {content, page: 0, size: 20, totalElements: content.length, totalPages});
 
-const renderPage = (route) => {
-    fetchRoutes({'GET /api/library/audit-log': route});
+const merge = (over) => entry({id: 7, action: 'GAME_MERGE', gameName: null, targetGameName: 'Hades', undoable: true,
+    detail: '"Hades (Switch)" into "Hades": 1 moved, 0 combined', ...over});
+
+const renderPage = (route, more = {}) => {
+    fetchRoutes({'GET /api/library/audit-log': route, ...more});
     render(<MemoryRouter><PreferencesProvider><AuditLogPage/></PreferencesProvider></MemoryRouter>);
 };
 
@@ -24,6 +29,8 @@ beforeEach(() => {
 
 afterEach(() => {
     cleanup();
+    vi.restoreAllMocks();
+    vi.clearAllMocks();
     localStorage.clear();
 });
 
@@ -58,4 +65,42 @@ describe('AuditLogPage', () => {
 
         expect(await screen.findByText('AUDIT.NO_ACCESS')).toBeTruthy();
     });
+
+    it('showsUndoOnlyOnAnUndoableMerge', async () => {
+        renderPage(answer([merge({}), merge({id: 8, undoable: false}), entry({id: 9, undoable: true})]));
+        await screen.findAllByText('AUDIT.ACTION.GAME_MERGE');
+
+        expect(screen.getAllByRole('button', {name: /AUDIT.UNDO.BUTTON/})).toHaveLength(1);
+    });
+
+    it('undoesAfterConfirmAndReloads', async () => {
+        const confirm = vi.spyOn(window, 'confirm').mockReturnValue(true);
+        renderPage(answer([merge({})]), {'POST /api/library/merges/7/undo': json(204, null)});
+
+        fireEvent.click(await screen.findByRole('button', {name: /AUDIT.UNDO.BUTTON/}));
+
+        await waitFor(() => expect(toast.success).toHaveBeenCalledWith('AUDIT.UNDO.DONE'));
+        expect(confirm).toHaveBeenCalledWith('AUDIT.UNDO.CONFIRM');
+        expect(fetch.mock.calls.filter(([, init]) => init?.method === 'POST')).toHaveLength(1);
+        expect(fetch.mock.calls.filter(([url]) => url.includes('/audit-log'))).toHaveLength(2);
+    });
+
+    it('doesNothingWhenTheConfirmIsCancelled', async () => {
+        vi.spyOn(window, 'confirm').mockReturnValue(false);
+        renderPage(answer([merge({})]));
+
+        fireEvent.click(await screen.findByRole('button', {name: /AUDIT.UNDO.BUTTON/}));
+
+        expect(fetch.mock.calls.filter(([, init]) => init?.method === 'POST')).toHaveLength(0);
+        expect(toast.success).not.toHaveBeenCalled();
+    });
+
+    it.each(['NEWER_MERGE', 'UNDO_EXPIRED'])('showsTheMessageOf%s', async (code) => {
+        vi.spyOn(window, 'confirm').mockReturnValue(true);
+        renderPage(answer([merge({})]), {'POST /api/library/merges/7/undo': json(409, {code})});
+
+        fireEvent.click(await screen.findByRole('button', {name: /AUDIT.UNDO.BUTTON/}));
+
+        await waitFor(() => expect(toast.error).toHaveBeenCalledWith(`AUDIT.UNDO.ERROR_CODES.${code}`));
+    });
 });

src/pages/GameDetail.jsx

@@ -47,6 +47,11 @@ export default function GameDetail() {
         shownLevel.current = {appid: data.appid, level: celebrationLevel(data)};
     }, [data]);
 
+    // An old key of a merged game: Core answers with the kept game.
+    useEffect(() => {
+        if (data && String(data.appid) !== appid) navigate(`/library/${data.appid}`, {replace: true});
+    }, [data, appid, navigate]);
+
     const manual = data?.source === 'MANUAL';
 
     return (
@@ -76,7 +81,7 @@ export default function GameDetail() {
                             <EyeOff className="size-4 shrink-0"/>{t('GAME_DETAIL.HIDDEN_NOTE')}
                         </div>
                     )}
-                    <GameHeroCard game={data} manual={manual} auditor={auditor} profileStyle={savedProfileStyle ?? currentUser?.profileStyle}
+                    <GameHeroCard game={data} auditor={auditor} profileStyle={savedProfileStyle ?? currentUser?.profileStyle}
                                   onCorrect={() => setCorrecting(true)} onMerge={() => setMerging(true)}
                                   onHiddenChanged={(hidden) => setData((d) => ({...d, hidden}))}
                                   onProfileStyleSaved={setSavedProfileStyle}/>

src/pages/GameDetail.test.jsx

@@ -64,7 +64,7 @@ describe('GameDetail', () => {
     });
 
     it('keeps the game shown when Core refuses', async () => {
-        answer({...game, source: 'STEAM', hidden: false}, {'PUT /api/library/games/220/hidden': json(409, {code: 'MANUAL_GAME'})});
+        answer({...game, source: 'STEAM', hidden: false}, {'PUT /api/library/games/220/hidden': json(500, {})});
         renderDetail();
 
         fireEvent.click(await screen.findByRole('button', {name: 'GAME_DETAIL.HIDE'}));
@@ -73,12 +73,19 @@ describe('GameDetail', () => {
         expect(screen.queryByText('GAME_DETAIL.HIDDEN_NOTE')).toBeNull();
     });
 
-    it('offers no hide for a game added by hand', async () => {
-        answer({...game, source: 'MANUAL', platform: 'PS5', hidden: false});
-        renderDetail();
+    it('hides a game added by hand and shows it again', async () => {
+        answer({...game, appid: -1942, source: 'MANUAL', platform: 'PS5', hidden: false},
+            {'PUT /api/library/games/-1942/hidden': echo});
+        renderDetail(-1942);
 
-        await screen.findByText('GAME_DETAIL.OPEN_IN_STEAM');
-        expect(screen.queryByRole('button', {name: 'GAME_DETAIL.HIDE'})).toBeNull();
+        fireEvent.click(await screen.findByRole('button', {name: 'GAME_DETAIL.HIDE'}));
+
+        expect(await screen.findByText('GAME_DETAIL.HIDDEN_NOTE')).toBeTruthy();
+        expect(screen.queryByText('GAME_DETAIL.OPEN_IN_STEAM')).toBeNull();
+
+        fireEvent.click(screen.getByRole('button', {name: 'GAME_DETAIL.UNHIDE'}));
+
+        await waitFor(() => expect(screen.queryByText('GAME_DETAIL.HIDDEN_NOTE')).toBeNull());
     });
 
     it('reports a broken achievement icon once and shows the empty tile', async () => {
@@ -419,4 +426,16 @@ describe('GameDetail session', () => {
         expect(toast.error).not.toHaveBeenCalled();
         expect(screen.queryByText('GAME_DETAIL.ERROR_LOAD')).toBeNull();
     });
+
+    it('replacesTheUrlOfAMergedKeyWithTheKeptGame', async () => {
+        fetchRoutes({
+            'GET /api/users/me': json(200, {settings: {}}),
+            'GET /api/library/games/-7': json(200, {...game, appid: 220, source: 'STEAM'}),
+            'GET /api/library/games/220': json(200, {...game, appid: 220, source: 'STEAM'}),
+        });
+        const {router} = renderDetail(-7);
+
+        await waitFor(() => expect(router.state.location.pathname).toBe('/library/220'));
+        expect(router.state.historyAction).toBe('REPLACE');
+    });
 });