feat(kanban): wide board animates, keeps header width and caps column width

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

frontend/src/App.tsx

@@ -164,8 +164,6 @@ export const App: React.FC = () => {
   const [deck, setDeck] = useState<Thought[]>([]);
   const [lists, setLists] = useState<SharedList[]>([]);
   const [activeTab, setActiveTab] = useState<ActiveTab>('triage');
-  // Kanban asked for the full window width (reported by the tasks view)
-  const [tasksWide, setTasksWide] = useState(false);
   const [previousTab, setPreviousTab] = useState<ActiveTab>('triage');
   const [selectedDocId, setSelectedDocId] = useState<string | null>(null);
   const [selectedBlockId, setSelectedBlockId] = useState<string | null>(null);
@@ -1170,9 +1168,7 @@ export const App: React.FC = () => {
       {/* Main Container */}
       {/* The workspace fills the window exactly and scrolls only inside the note, never the page */}
       <main
-        className={`flex-1 w-full mx-auto px-3 sm:px-4 pt-3 pb-24 ${
-          activeTab === 'tasks' && tasksWide ? 'lg:max-w-none lg:px-6' : 'max-w-6xl'
-        } ${
+        className={`flex-1 max-w-6xl w-full mx-auto px-3 sm:px-4 pt-3 pb-24 ${
           activeTab === 'workspace' ? 'min-h-0 flex flex-col sm:pb-0' : 'sm:pb-6'
         }`}
       >
@@ -1196,7 +1192,6 @@ export const App: React.FC = () => {
                 refreshTrigger={refreshRevision}
                 initialSelectedTaskId={selectedTaskId}
                 openTasksCount={stats.tasksOpenCount}
-                onWideChange={setTasksWide}
               />
             )}
 

frontend/src/features/triage/TasksView.tsx

@@ -62,10 +62,25 @@ interface TasksViewProps {
   refreshTrigger?: number;
   initialSelectedTaskId?: string | null;
   openTasksCount?: number; // all open tasks incl. shared lists (same as the nav bar counter)
-  onWideChange?: (wide: boolean) => void; // Kanban stretched to the full window width
 }
 
 const KANBAN_WIDE_KEY = 'mindsift:kanban_wide';
+// Wide Kanban: a column grows to at most this width, the board stays centred
+const KANBAN_COL_MAX = 380;
+const KANBAN_GAP = 12; // gap-3
+
+// Only the board leaves the page column (header and "new task" keep their width): its width follows
+// the columns (at most KANBAN_COL_MAX each, at most the window) and a margin keeps it centred – a
+// negative one when it is wider than the page column. Width and margin are animated.
+const kanbanBoardStyle = (wide: boolean, columns: number): React.CSSProperties => {
+  if (!wide) return { '--kanban-w': '100%', '--kanban-ml': '0px' } as React.CSSProperties;
+  const w = `min(100vw - 4rem, ${columns * KANBAN_COL_MAX + (columns - 1) * KANBAN_GAP}px)`;
+  return {
+    '--kanban-cols': columns,
+    '--kanban-w': w,
+    '--kanban-ml': `calc((100% - ${w}) / 2)`,
+  } as React.CSSProperties;
+};
 
 type TasksSession = { listId: string; viewMode: 'list' | 'kanban' };
 
@@ -76,7 +91,6 @@ export const TasksView: React.FC<TasksViewProps> = ({
   refreshTrigger = 0,
   initialSelectedTaskId,
   openTasksCount,
-  onWideChange,
 }) => {
   // Open list and view survive switching to other tabs (like the workspace's open note)
   const [viewMode, setViewMode] = useState<'list' | 'kanban'>(() =>
@@ -100,10 +114,6 @@ export const TasksView: React.FC<TasksViewProps> = ({
     }
   };
   const isKanbanWide = viewMode === 'kanban' && kanbanWide;
-  useEffect(() => {
-    onWideChange?.(isKanbanWide);
-  }, [isKanbanWide, onWideChange]);
-  useEffect(() => () => onWideChange?.(false), [onWideChange]);
   const [filter, setFilter] = useState<'open' | 'done' | 'discarded'>('open');
   const [tasks, setTasks] = useState<Thought[]>([]);
   const [taskLists, setTaskLists] = useState<TaskList[]>([]);
@@ -2214,10 +2224,10 @@ export const TasksView: React.FC<TasksViewProps> = ({
         /* DYNAMIC KANBAN BOARD */
         <div className="space-y-2">
           <div
-            className={`grid grid-cols-1 md:grid-cols-2 gap-3 pt-1 ${
+            className={`grid grid-cols-1 md:grid-cols-2 gap-3 pt-1 lg:w-[var(--kanban-w)] lg:ml-[var(--kanban-ml)] transition-[width,margin] duration-300 ease-out ${
               isKanbanWide ? 'lg:grid-cols-[repeat(var(--kanban-cols),minmax(0,1fr))]' : 'lg:grid-cols-4'
             }`}
-            style={isKanbanWide ? ({ '--kanban-cols': activeColumns.length } as React.CSSProperties) : undefined}
+            style={kanbanBoardStyle(isKanbanWide, activeColumns.length)}
           >
             {activeColumns.map((col, colIdx) => {
               const colTasks = kanbanTasks.filter((t) => {