feat(tasks): remember list or Kanban per task list

Each task list (and "Alle Aufgaben") keeps its own view on this device;
a single remembered Kanban view from before carries over to its list.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/triage/TasksView.tsx

@@ -92,7 +92,15 @@ const kanbanBoardStyle = (wide: boolean, columns: number): React.CSSProperties =
 };
 
 type GroupBy = 'none' | 'list' | 'tag' | 'status' | 'priority' | 'due';
-type TasksSession = { listId: string; viewMode: 'list' | 'kanban'; groupAll: GroupBy; groupList: GroupBy };
+type ViewMode = 'list' | 'kanban';
+// viewModes: list or Kanban per task list ("all" for Alle Aufgaben); viewMode is the old single value
+type TasksSession = {
+  listId: string;
+  viewModes: Record<string, ViewMode>;
+  viewMode?: ViewMode;
+  groupAll: GroupBy;
+  groupList: GroupBy;
+};
 
 // "Alle Aufgaben" is grouped by task list unless the user picks something else; a single list has no
 // grouping by default (grouping it by list would give one group)
@@ -123,11 +131,20 @@ export const TasksView: React.FC<TasksViewProps> = ({
   onInitialTaskShown,
   openTasksCount,
 }) => {
-  // Open list, view and grouping are remembered on this device (new tab, restart of the installed app)
+  // Open list, view per list and grouping are remembered on this device (new tab, restart of the
+  // installed app)
   const remembered = useMemo(() => readViewMemory<TasksSession>('tasks'), []);
-  const [viewMode, setViewMode] = useState<'list' | 'kanban'>(() =>
-    remembered.viewMode === 'kanban' ? 'kanban' : 'list'
-  );
+  const [viewModes, setViewModes] = useState<Record<string, ViewMode>>(() => {
+    const out: Record<string, ViewMode> = {};
+    if (remembered.viewModes && typeof remembered.viewModes === 'object') {
+      for (const [id, mode] of Object.entries(remembered.viewModes)) {
+        if (mode === 'kanban') out[id] = 'kanban';
+      }
+    } else if (remembered.viewMode === 'kanban' && remembered.listId) {
+      out[remembered.listId] = 'kanban'; // stored before views were kept per list
+    }
+    return out;
+  });
   const [groupAll, setGroupAll] = useState<GroupBy>(() =>
     remembered.groupAll && remembered.groupAll in GROUP_LABELS ? remembered.groupAll : DEFAULT_GROUP_ALL
   );
@@ -153,13 +170,25 @@ export const TasksView: React.FC<TasksViewProps> = ({
       // only a convenience
     }
   };
-  const isKanbanWide = viewMode === 'kanban' && kanbanWide;
   const [filter, setFilter] = useState<'open' | 'done' | 'discarded'>('open');
   const [tasks, setTasks] = useState<Thought[]>([]);
   const [taskLists, setTaskLists] = useState<TaskList[]>([]);
   const [selectedListId, setSelectedListId] = useState<string>(
     () => remembered.listId || 'all'
   );
+  const viewMode: ViewMode = viewModes[selectedListId] || 'list';
+  // Only Kanban is stored; the list view is the default
+  const setViewMode = useCallback(
+    (mode: ViewMode) =>
+      setViewModes((prev) => {
+        const next = { ...prev };
+        if (mode === 'kanban') next[selectedListId] = 'kanban';
+        else delete next[selectedListId];
+        return next;
+      }),
+    [selectedListId]
+  );
+  const isKanbanWide = viewMode === 'kanban' && kanbanWide;
   const isAllTasks = selectedListId === 'all';
   const groupBy: GroupBy = isAllTasks ? groupAll : groupList;
   const setGroupBy = (g: GroupBy) => (isAllTasks ? setGroupAll(g) : setGroupList(g));
@@ -169,8 +198,8 @@ export const TasksView: React.FC<TasksViewProps> = ({
     .filter((id) => isAllTasks || id !== 'list')
     .map((id) => ({ id, label: GROUP_LABELS[id] }));
   useEffect(() => {
-    writeViewMemory<TasksSession>('tasks', { listId: selectedListId, viewMode, groupAll, groupList });
-  }, [selectedListId, viewMode, groupAll, groupList]);
+    writeViewMemory<TasksSession>('tasks', { listId: selectedListId, viewModes, groupAll, groupList });
+  }, [selectedListId, viewModes, groupAll, groupList]);
   const [teams, setTeams] = useState<Team[]>([]);
   const [collaborators, setCollaborators] = useState<User[]>([]);
   // Task trash of the selected list (or all): deleted tasks and cleared or cleaned-up completed ones
@@ -1538,6 +1567,7 @@ export const TasksView: React.FC<TasksViewProps> = ({
     selectedTag,
     groupBy,
     defaultGroupBy,
+    setViewMode,
     sortBy,
     openTasks.length,
     doneTasks.length,