compact todo groups: ride the "+" on the last visible row

In compact layout the add-to-do menu no longer takes a row of its
own — it now renders inline on the last visible to-do, saving one
line per group. A compact group is guaranteed to have at least one
visible to-do (CategoryLane hides it otherwise), so there's always
a row to attach it to; a defensive fallback keeps the "+" reachable
in the off chance that invariant ever changes. Non-compact layout
(popover, AI add, archive, progress pie) is unchanged.

components/board/group-card.tsx

@@ -6,6 +6,7 @@ import { CSS } from "@dnd-kit/utilities";
 import { useTheme } from "next-themes";
 import {
   Archive,
+  ChevronRight,
   ClipboardList,
   GripVertical,
   MoreVertical,
@@ -94,6 +95,7 @@ export function GroupCard({ group }: { group: GroupDTO }) {
   const [todoAiOpen, setTodoAiOpen] = useState(false);
   const [todoCreateOpen, setTodoCreateOpen] = useState(false);
   const [statusUpdateOpen, setStatusUpdateOpen] = useState(false);
+  const [expandedWhileComplete, setExpandedWhileComplete] = useState(false);
 
   const {
     attributes,
@@ -143,6 +145,26 @@ export function GroupCard({ group }: { group: GroupDTO }) {
   // from the list entirely rather than shown crossed-out.
   const visibleTodos = compact ? group.todos.filter((t) => !t.completed) : group.todos;
 
+  // In the default view, a fully-checked-off group collapses down to just
+  // its header (title, notes icon, kebab menu) with a disclosure triangle
+  // in place of the drag-grip dots, so a board full of "done" groups
+  // doesn't stay as visually loud as one still full of open work. The
+  // triangle re-expands it back to the normal full card. Compact already
+  // hides finished groups outright (see CategoryLane), so this only
+  // applies to the default view.
+  const showDisclosure = !compact && canArchive;
+  // Reset back to collapsed each time the group freshly becomes fully
+  // done, rather than remembering a stale expanded choice from its last
+  // completion cycle. Adjusting state during render (comparing against
+  // last render's value) instead of in a useEffect avoids an extra render
+  // pass -- see https://react.dev/learn/you-might-not-need-an-effect.
+  const [wasComplete, setWasComplete] = useState(canArchive);
+  if (canArchive !== wasComplete) {
+    setWasComplete(canArchive);
+    if (canArchive) setExpandedWhileComplete(false);
+  }
+  const isCollapsed = showDisclosure && !expandedWhileComplete;
+
   return (
     <>
       <div
@@ -168,9 +190,26 @@ export function GroupCard({ group }: { group: GroupDTO }) {
             className="group flex min-w-0 flex-1 cursor-grab touch-none items-start gap-1 rounded-md outline-none active:cursor-grabbing focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-1"
             aria-label={`Drag to move ${group.title}`}
           >
+            {showDisclosure ? (
+              <button
+                type="button"
+                onClick={(e) => {
+                  e.stopPropagation();
+                  setExpandedWhileComplete((v) => !v);
+                }}
+                className="mt-1 flex shrink-0 items-center justify-center text-muted-foreground/60 hover:text-foreground"
+                aria-label={expandedWhileComplete ? `Collapse ${group.title}` : `Expand ${group.title}`}
+                aria-expanded={expandedWhileComplete}
+              >
+                <ChevronRight
+                  className={cn("size-4 transition-transform", expandedWhileComplete && "rotate-90")}
+                />
+              </button>
+            ) : (
               <span className="mt-1 flex shrink-0 items-center justify-center text-muted-foreground/60 group-hover:text-muted-foreground">
                 <GripVertical className="size-4" />
               </span>
+            )}
             <h3 className="min-w-0 flex-1 truncate pt-1 text-sm font-semibold">{group.title}</h3>
           </div>
           <div className="flex shrink-0 items-center">
@@ -207,6 +246,8 @@ export function GroupCard({ group }: { group: GroupDTO }) {
           </div>
         </div>
 
+        {!isCollapsed && (
+          <>
             <ul className="mt-1 space-y-1">
               {visibleTodos.map((todo, index) => {
                 const todoButton = (
@@ -229,8 +270,8 @@ export function GroupCard({ group }: { group: GroupDTO }) {
                 // In compact, the "+" rides along on the last visible row
                 // instead of taking a row of its own -- one less line per
                 // group. (A compact group always has at least one unchecked
-            // to-do -- CategoryLane hides it otherwise -- so there's always
+                // to-do -- CategoryLane hides it otherwise -- so there's
-            // a last row to put it on.)
+                // always a last row to put it on.)
                 const isLastRow = compact && index === visibleTodos.length - 1;
 
                 return (
@@ -265,8 +306,9 @@ export function GroupCard({ group }: { group: GroupDTO }) {
 
             {compact ? (
               // Defensive fallback -- shouldn't normally happen, since
-          // CategoryLane already hides a compact group with zero visible
+              // CategoryLane already hides a compact group with zero
-          // to-dos, but keeps the "+" reachable if that ever changes.
+              // visible to-dos, but keeps the "+" reachable if that ever
+              // changes.
               visibleTodos.length === 0 && (
                 <div className="mt-1 flex justify-end">
                   <AddTodoMenu
@@ -314,6 +356,8 @@ export function GroupCard({ group }: { group: GroupDTO }) {
                 />
               </>
             )}
+          </>
+        )}
       </div>
 
       {editingTodo && (