feat(core): implement git worktree checkpoint system

Add comprehensive worktree management system to enable task isolation and rollback capabilities. This allows users to revert agent changes if they don't satisfy requirements or break functionality.

Key components:
- New WorktreeManager service for branch and worktree operations
- GitDiffPanel component for visualizing changes
- Enhanced UI components with worktree integration
- Auto-mode service enhancements for worktree workflow

Modified files: worktree-manager.js, git-diff-panel.tsx, main.js, preload.js, feature-loader.js, agent-output-modal.tsx, board-view.tsx, kanban-card.tsx, electron.ts, app-store.ts, electron.d.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

app/src/components/views/kanban-card.tsx

@@ -49,6 +49,9 @@ import {
   FileText,
   MoreVertical,
   AlertCircle,
+  GitBranch,
+  Undo2,
+  GitMerge,
 } from "lucide-react";
 import { CountUpTimer } from "@/components/ui/count-up-timer";
 import { getElectronAPI } from "@/lib/electron";
@@ -72,6 +75,8 @@ interface KanbanCardProps {
   onMoveBackToInProgress?: () => void;
   onFollowUp?: () => void;
   onCommit?: () => void;
+  onRevert?: () => void;
+  onMerge?: () => void;
   hasContext?: boolean;
   isCurrentAutoTask?: boolean;
   shortcutKey?: string;
@@ -93,6 +98,8 @@ export function KanbanCard({
   onMoveBackToInProgress,
   onFollowUp,
   onCommit,
+  onRevert,
+  onMerge,
   hasContext,
   isCurrentAutoTask,
   shortcutKey,
@@ -101,9 +108,13 @@ export function KanbanCard({
 }: KanbanCardProps) {
   const [isDeleteDialogOpen, setIsDeleteDialogOpen] = useState(false);
   const [isSummaryDialogOpen, setIsSummaryDialogOpen] = useState(false);
+  const [isRevertDialogOpen, setIsRevertDialogOpen] = useState(false);
   const [agentInfo, setAgentInfo] = useState<AgentTaskInfo | null>(null);
   const { kanbanCardDetailLevel } = useAppStore();
 
+  // Check if feature has worktree
+  const hasWorktree = !!feature.branchName;
+
   // Helper functions to check what should be shown based on detail level
   const showSteps =
     kanbanCardDetailLevel === "standard" ||
@@ -246,11 +257,33 @@ export function KanbanCard({
           <span>Errored</span>
         </div>
       )}
+      {/* Branch badge - show when feature has a worktree */}
+      {hasWorktree && !isCurrentAutoTask && (
+        <div
+          className={cn(
+            "absolute px-1.5 py-0.5 text-[10px] font-medium rounded flex items-center gap-1 z-10",
+            "bg-purple-500/20 border border-purple-500/50 text-purple-400",
+            // Position below error badge if present, otherwise use normal position
+            feature.error || feature.skipTests
+              ? "top-8 left-2"
+              : shortcutKey
+                ? "top-2 left-10"
+                : "top-2 left-2"
+          )}
+          data-testid={`branch-badge-${feature.id}`}
+          title={`Branch: ${feature.branchName}`}
+        >
+          <GitBranch className="w-3 h-3" />
+          <span className="truncate max-w-[100px]">{feature.branchName?.replace("feature/", "")}</span>
+        </div>
+      )}
       <CardHeader
         className={cn(
           "p-3 pb-2 block", // Reset grid layout to block for custom kanban card layout
           // Add extra top padding when badges are present to prevent text overlap
-          (feature.skipTests || feature.error || shortcutKey) && "pt-10"
+          (feature.skipTests || feature.error || shortcutKey) && "pt-10",
+          // Add even more top padding when both badges and branch are shown
+          hasWorktree && (feature.skipTests || feature.error) && "pt-14"
         )}
       >
         {isCurrentAutoTask && (
@@ -615,6 +648,23 @@ export function KanbanCard({
           )}
           {!isCurrentAutoTask && feature.status === "waiting_approval" && (
             <>
+              {/* Revert button - only show when worktree exists */}
+              {hasWorktree && onRevert && (
+                <Button
+                  variant="ghost"
+                  size="sm"
+                  className="h-7 text-xs text-red-400 hover:text-red-300 hover:bg-red-500/20"
+                  onClick={(e) => {
+                    e.stopPropagation();
+                    setIsRevertDialogOpen(true);
+                  }}
+                  data-testid={`revert-${feature.id}`}
+                  title="Discard all changes and move back to backlog"
+                >
+                  <Undo2 className="w-3 h-3 mr-1" />
+                  Revert
+                </Button>
+              )}
               {/* Follow-up prompt button */}
               {onFollowUp && (
                 <Button
@@ -631,8 +681,25 @@ export function KanbanCard({
                   Follow-up
                 </Button>
               )}
-              {/* Commit and verify button */}
-              {onCommit && (
+              {/* Merge button - only show when worktree exists */}
+              {hasWorktree && onMerge && (
+                <Button
+                  variant="default"
+                  size="sm"
+                  className="flex-1 h-7 text-xs bg-purple-600 hover:bg-purple-700"
+                  onClick={(e) => {
+                    e.stopPropagation();
+                    onMerge();
+                  }}
+                  data-testid={`merge-${feature.id}`}
+                  title="Merge changes into main branch"
+                >
+                  <GitMerge className="w-3 h-3 mr-1" />
+                  Merge
+                </Button>
+              )}
+              {/* Commit and verify button - show when no worktree */}
+              {!hasWorktree && onCommit && (
                 <Button
                   variant="default"
                   size="sm"
@@ -736,6 +803,49 @@ export function KanbanCard({
           </DialogFooter>
         </DialogContent>
       </Dialog>
+
+      {/* Revert Confirmation Dialog */}
+      <Dialog open={isRevertDialogOpen} onOpenChange={setIsRevertDialogOpen}>
+        <DialogContent data-testid="revert-confirmation-dialog">
+          <DialogHeader>
+            <DialogTitle className="flex items-center gap-2 text-red-400">
+              <Undo2 className="w-5 h-5" />
+              Revert Changes
+            </DialogTitle>
+            <DialogDescription>
+              This will discard all changes made by the agent and move the feature back to the backlog.
+              {feature.branchName && (
+                <span className="block mt-2 font-medium">
+                  Branch <code className="bg-muted px-1 py-0.5 rounded">{feature.branchName}</code> will be deleted.
+                </span>
+              )}
+              <span className="block mt-2 text-red-400 font-medium">
+                This action cannot be undone.
+              </span>
+            </DialogDescription>
+          </DialogHeader>
+          <DialogFooter>
+            <Button
+              variant="ghost"
+              onClick={() => setIsRevertDialogOpen(false)}
+              data-testid="cancel-revert-button"
+            >
+              Cancel
+            </Button>
+            <Button
+              variant="destructive"
+              onClick={() => {
+                setIsRevertDialogOpen(false);
+                onRevert?.();
+              }}
+              data-testid="confirm-revert-button"
+            >
+              <Undo2 className="w-4 h-4 mr-2" />
+              Revert Changes
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
     </Card>
   );
 }