feat: implement Undo/Redo/Timeline and Fork Features and fixed opencode.json reading issue on broken json (#99)

* feat: add /undo, /redo, /timeline slash commands and fork button

- Add /undo command to revert to previous user message
- Add /redo command to redo previously undone messages
- Add /timeline command to show conversation history
- Add fork button on user messages (hover) to create new session
- Add TimelineDialog component for navigating conversation history
- Show undo/redo/timeline in autocomplete when session exists
- Fix fork to use SDK session.fork API
- Silent no-op behavior for undo/redo when no messages (matches OpenCode CLI)

* fix: correct fork session endpoint and session switching

- Add hybrid SDK approach using v1 for existing methods and v2 for fork only
- v2 SDK has correct endpoint /session/{sessionID}/fork instead of broken /session/{id}/fork
- Fix forkFromMessage to use setCurrentSession instead of direct set
- Ensures both useSessionStore and useSessionManagementStore are consistent
- Fixes issue where forked sessions appeared empty until sending a new message

* fix: use direct fetch for fork to avoid v2 SDK build errors

- Remove v2 SDK imports and hybrid SDK approach
- Use direct fetch() call to /api/session/{sessionID}/fork endpoint
- Avoids type conflicts between v1 and v2 SDK
- Bypasses broken v1 SDK fork endpoint (wrong path parameter)
- All codebase now uses v1 SDK consistently

* fix: use jsonc-parser for config file parsing

- Replace strip-json-comments + JSON.parse with jsonc-parser
- Handles comments, trailing commas, and unquoted keys
- Matches OpenCode CLI config parsing behavior
- Fixes SyntaxError when reading global opencode.json config

* feat: improve timeline dialog with loading state and search

- Add loading spinner on fork button during operation (~30s on big sessions)
- Refresh session list after fork so new session appears in sidebar immediately
- Add search bar to filter messages by prompt text content
- Show 'No messages found' when search has no results
- Disable fork button while forking to prevent duplicate operations

AGENTS.md

@@ -113,6 +113,7 @@ SDK-managed SSE with AsyncGenerator, temp->real session ID swap (optimistic UI),
 - Run `bun run lint` and `bun run type-check` before finalizing changes
 - Adding `eslint-disable` requires justification in a comment explaining why typing is impossible
 - Do **not** use `any` or `unknown` casts as escape hatches; build narrow adapter interfaces instead
+
 - Refactors or new features must keep existing lint/type baselines green
 
 ### Theme Integration
@@ -128,6 +129,7 @@ SDK-managed SSE with AsyncGenerator, temp->real session ID swap (optimistic UI),
 - **Functional components**: Exclusive use of function components with hooks
 - **Custom hooks**: Extract logic for reusability
 - **Type-first development**: Comprehensive TypeScript usage
+- opencode repo is in ../opencode dir from this pwd dir check the codebase for any api undersatning . dont change opencode dir . 
 - **Component composition**: Prefer composition over inheritance
 
 ## Feature Implementation Map

bun.lock

@@ -41,7 +41,6 @@
         "remark-gfm": "^4.0.1",
         "simple-git": "^3.28.0",
         "sonner": "^2.0.7",
-        "strip-json-comments": "^5.0.3",
         "tailwind-merge": "^3.3.1",
         "yaml": "^2.8.1",
         "zustand": "^5.0.8",
@@ -120,7 +119,7 @@
         "clsx": "^2.1.1",
         "cmdk": "^1.1.1",
         "express": "^5.1.0",
-        "ghostty-web": "0.3.0",
+        "ghostty-web": "^0.4.0",
         "heic2any": "^0.0.4",
         "http-proxy-middleware": "^3.0.5",
         "motion": "^12.23.24",
@@ -212,6 +211,7 @@
         "express": "^5.1.0",
         "ghostty-web": "0.3.0",
         "http-proxy-middleware": "^3.0.5",
+        "jsonc-parser": "^3.3.1",
         "next-themes": "^0.4.6",
         "node-pty": "^1.1.0",
         "react": "^19.1.1",
@@ -2586,6 +2586,8 @@
 
     "@malept/flatpak-bundler/fs-extra": ["fs-extra@9.1.0", "", { "dependencies": { "at-least-node": "^1.0.0", "graceful-fs": "^4.2.0", "jsonfile": "^6.0.1", "universalify": "^2.0.0" } }, "sha512-hcg3ZmepS30/7BSFqRvoo3DOMQu7IjqxO5nCDt+zM9XWjb33Wg7ziNT+Qvqbuc3+gWpzO02JubVyk2G4Zvo1OQ=="],
 
+    "@openchamber/ui/ghostty-web": ["ghostty-web@0.4.0", "", {}, "sha512-0puDBik2qapbD/QQBW9o5ZHfXnZBqZWx/ctBiVtKZ6ZLds4NYb+wZuw1cRLXZk9zYovIQ908z3rvFhexAvc5Hg=="],
+
     "@radix-ui/react-collection/@radix-ui/react-slot": ["@radix-ui/react-slot@1.2.3", "", { "dependencies": { "@radix-ui/react-compose-refs": "1.1.2" }, "peerDependencies": { "@types/react": "*", "react": "^16.8 || ^17.0 || ^18.0 || ^19.0 || ^19.0.0-rc" }, "optionalPeers": ["@types/react"] }, "sha512-aeNmHnBxbi2St0au6VBVC7JXFlhLlOnvIIlePNniyUNAClzmtAUEY8/pBiK3iHjufOlwA+c20/8jngo7xcrg8A=="],
 
     "@radix-ui/react-dialog/@radix-ui/react-slot": ["@radix-ui/react-slot@1.2.3", "", { "dependencies": { "@radix-ui/react-compose-refs": "1.1.2" }, "peerDependencies": { "@types/react": "*", "react": "^16.8 || ^17.0 || ^18.0 || ^19.0 || ^19.0.0-rc" }, "optionalPeers": ["@types/react"] }, "sha512-aeNmHnBxbi2St0au6VBVC7JXFlhLlOnvIIlePNniyUNAClzmtAUEY8/pBiK3iHjufOlwA+c20/8jngo7xcrg8A=="],

package.json

@@ -93,7 +93,6 @@
     "remark-gfm": "^4.0.1",
     "simple-git": "^3.28.0",
     "sonner": "^2.0.7",
-    "strip-json-comments": "^5.0.3",
     "tailwind-merge": "^3.3.1",
     "yaml": "^2.8.1",
     "zustand": "^5.0.8"

packages/ui/package.json

@@ -27,11 +27,11 @@
     "@radix-ui/react-tooltip": "^1.2.8",
     "@remixicon/react": "^4.7.0",
     "@types/react-syntax-highlighter": "^15.5.13",
-    "ghostty-web": "0.3.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
     "express": "^5.1.0",
+    "ghostty-web": "^0.4.0",
     "heic2any": "^0.0.4",
     "http-proxy-middleware": "^3.0.5",
     "motion": "^12.23.24",

packages/ui/src/components/chat/ChatContainer.tsx

@@ -3,6 +3,7 @@ import { RiArrowDownLine } from '@remixicon/react';
 
 import { ChatInput } from './ChatInput';
 import { useSessionStore } from '@/stores/useSessionStore';
+import { useUIStore } from '@/stores/useUIStore';
 import { Skeleton } from '@/components/ui/skeleton';
 import ChatEmptyState from './ChatEmptyState';
 import MessageList from './MessageList';
@@ -11,6 +12,7 @@ import { useChatScrollManager } from '@/hooks/useChatScrollManager';
 import { useDeviceInfo } from '@/lib/device';
 import { Button } from '@/components/ui/button';
 import { OverlayScrollbar } from '@/components/ui/OverlayScrollbar';
+import { TimelineDialog } from './TimelineDialog';
 
 export const ChatContainer: React.FC = () => {
     const {
@@ -33,6 +35,11 @@ export const ChatContainer: React.FC = () => {
         newSessionDraft,
     } = useSessionStore();
 
+    const {
+        isTimelineDialogOpen,
+        setTimelineDialogOpen,
+    } = useUIStore();
+
     const streamingMessageId = React.useMemo(() => {
         if (!currentSessionId) return null;
         return streamingMessageIds.get(currentSessionId) ?? null;
@@ -130,6 +137,27 @@ export const ChatContainer: React.FC = () => {
         }
     }, [currentSessionId, isLoadingOlder, loadMoreMessages, scrollRef]);
 
+    // Scroll to a specific message by ID (for timeline dialog)
+    const scrollToMessage = React.useCallback((messageId: string) => {
+        const container = scrollRef.current;
+        if (!container) return;
+
+        // Find the message element by looking for data-message-id attribute
+        const messageElement = container.querySelector(`[data-message-id="${messageId}"]`) as HTMLElement;
+        if (messageElement) {
+            // Scroll to the message with some padding (50px from top)
+            const containerRect = container.getBoundingClientRect();
+            const messageRect = messageElement.getBoundingClientRect();
+            const offset = 50;
+
+            const scrollTop = messageRect.top - containerRect.top + container.scrollTop - offset;
+            container.scrollTo({
+                top: scrollTop,
+                behavior: 'smooth'
+            });
+        }
+    }, [scrollRef]);
+
     React.useEffect(() => {
         if (!currentSessionId) {
             return;
@@ -199,7 +227,7 @@ export const ChatContainer: React.FC = () => {
                     style={isMobile ? { paddingBottom: 'var(--oc-keyboard-inset, 0px)' } : undefined}
                 >
                     <div className="flex-1 overflow-y-auto p-4 bg-background">
-                    <div className="chat-column space-y-4">
+                        <div className="chat-column space-y-4">
                             {[1, 2, 3].map((i) => (
                                 <div key={i} className="flex gap-3 p-4">
                                     <Skeleton className="h-8 w-8 rounded-full" />
@@ -246,7 +274,6 @@ export const ChatContainer: React.FC = () => {
                         ref={scrollRef}
                         style={{
                             contain: 'strict',
-
                             ['--scroll-shadow-size' as string]: '48px',
                         }}
                         data-scroll-shadow="true"
@@ -296,6 +323,12 @@ export const ChatContainer: React.FC = () => {
                 )}
                 <ChatInput scrollToBottom={scrollToBottom} />
             </div>
+
+            <TimelineDialog
+                open={isTimelineDialogOpen}
+                onOpenChange={setTimelineDialogOpen}
+                onScrollToMessage={scrollToMessage}
+            />
         </div>
     );
 };

packages/ui/src/components/chat/ChatInput.tsx

@@ -82,7 +82,7 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
 
     const { currentProviderId, currentModelId, currentAgentName, setAgent, getVisibleAgents } = useConfigStore();
     const agents = getVisibleAgents();
-    const { isMobile, inputBarOffset, isKeyboardOpen } = useUIStore();
+    const { isMobile, inputBarOffset, isKeyboardOpen, setTimelineDialogOpen } = useUIStore();
     const { working } = useAssistantStatus();
     const [showAbortStatus, setShowAbortStatus] = React.useState(false);
     const abortTimeoutRef = React.useRef<ReturnType<typeof setTimeout> | null>(null);
@@ -355,7 +355,7 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
             textareaRef.current?.blur();
         }
 
-        // Handle /summarize command scroll
+        // Handle slash commands locally before sending
         const normalizedCommand = primaryText.trimStart();
         if (normalizedCommand.startsWith('/')) {
             const commandName = normalizedCommand
@@ -363,7 +363,29 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
                 .trim()
                 .split(/\s+/)[0]
                 ?.toLowerCase();
-            if (commandName === 'summarize') {
+
+            // NEW: /undo - revert to last message (populates input with reverted message text)
+            if (commandName === 'undo' && currentSessionId) {
+                await useSessionStore.getState().handleSlashUndo(currentSessionId);
+                // Don't clear message - pendingInputText will populate it with reverted message
+                scrollToBottom?.({ instant: true, force: true });
+                return; // Don't send to assistant
+            }
+            // NEW: /redo - unrevert or partial redo (populates input with message text)
+            else if (commandName === 'redo' && currentSessionId) {
+                await useSessionStore.getState().handleSlashRedo(currentSessionId);
+                // Don't clear message - pendingInputText will populate it
+                scrollToBottom?.({ instant: true, force: true });
+                return; // Don't send to assistant
+            }
+            // NEW: /timeline - open timeline dialog
+            else if (commandName === 'timeline' && currentSessionId) {
+                setTimelineDialogOpen(true);
+                setMessage('');
+                return; // Don't send to assistant
+            }
+            // Existing: /summarize command scroll
+            else if (commandName === 'summarize') {
                 scrollToBottom?.({ instant: true, force: true });
             }
         }

packages/ui/src/components/chat/ChatMessage.tsx

@@ -578,12 +578,19 @@ const ChatMessage: React.FC<ChatMessageProps> = ({
     }, [messageTextContent]);
 
     const revertToMessage = useSessionStore((state) => state.revertToMessage);
+    const forkFromMessage = useSessionStore((state) => state.forkFromMessage);
 
     const handleRevert = React.useCallback(() => {
         if (!sessionId || !message.info.id) return;
         revertToMessage(sessionId, message.info.id);
     }, [sessionId, message.info.id, revertToMessage]);
 
+    // NEW: Fork handler
+    const handleFork = React.useCallback(() => {
+        if (!sessionId || !message.info.id) return;
+        forkFromMessage(sessionId, message.info.id);
+    }, [sessionId, message.info.id, forkFromMessage]);
+
     const handleToggleTool = React.useCallback((toolId: string) => {
         setExpandedTools((prev) => {
             const next = new Set(prev);
@@ -788,6 +795,7 @@ const ChatMessage: React.FC<ChatMessageProps> = ({
                                         onAuxiliaryContentComplete={handleAuxiliaryContentComplete}
                                         agentMention={agentMention}
                                         onRevert={handleRevert}
+                                        onFork={isUser ? handleFork : undefined}
                                         errorMessage={assistantErrorText}
                                     />
                                 </div>

packages/ui/src/components/chat/CommandAutocomplete.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { RiCommandLine, RiFileLine, RiFlashlightLine, RiRefreshLine, RiScissorsLine, RiTerminalBoxLine } from '@remixicon/react';
+import { RiCommandLine, RiFileLine, RiFlashlightLine, RiRefreshLine, RiScissorsLine, RiTerminalBoxLine, RiArrowGoBackLine, RiArrowGoForwardLine, RiTimeLine } from '@remixicon/react';
 import { cn } from '@/lib/utils';
 import { opencodeClient } from '@/lib/opencode/client';
 import { useSessionStore } from '@/stores/useSessionStore';
@@ -29,15 +29,17 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
   onCommandSelect,
   onClose
 }, ref) => {
-  const { hasMessagesInCurrentSession } = useSessionStore(
+  const { hasMessagesInCurrentSession, currentSessionId } = useSessionStore(
     useShallow((state) => {
       const sessionId = state.currentSessionId;
       const messageCount = sessionId ? (state.messages.get(sessionId)?.length ?? 0) : 0;
       return {
         hasMessagesInCurrentSession: messageCount > 0,
+        currentSessionId: sessionId,
       };
     })
   );
+  const hasSession = Boolean(currentSessionId);
 
   const [commands, setCommands] = React.useState<CommandInfo[]>([]);
   const [loading, setLoading] = React.useState(false);
@@ -79,9 +81,18 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
         }));
 
         const builtInCommands: CommandInfo[] = [
-          ...(hasMessagesInCurrentSession
+          ...(hasSession && !hasMessagesInCurrentSession
-            ? []
+            ? [{ name: 'init', description: 'Create/update AGENTS.md file', isBuiltIn: true }]
-            : [{ name: 'init', description: 'Create/update AGENTS.md file', isBuiltIn: true }]),
+            : []
+          ),
+          ...(hasSession  // Show when session exists, not when hasMessages
+            ? [
+                { name: 'undo', description: 'Undo the last message', isBuiltIn: true },
+                { name: 'redo', description: 'Redo previously undone messages', isBuiltIn: true },
+                { name: 'timeline', description: 'Jump to a specific message', isBuiltIn: true },
+              ]
+            : []
+          ),
           { name: 'summarize', description: 'Generate a summary of the current session', isBuiltIn: true },
         ];
 
@@ -114,9 +125,18 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
 
         const allowInitCommand = !hasMessagesInCurrentSession;
         const builtInCommands: CommandInfo[] = [
-          ...(hasMessagesInCurrentSession
+          ...(hasSession && !hasMessagesInCurrentSession
-            ? []
+            ? [{ name: 'init', description: 'Create/update AGENTS.md file', isBuiltIn: true }]
-            : [{ name: 'init', description: 'Create/update AGENTS.md file', isBuiltIn: true }]),
+            : []
+          ),
+          ...(hasSession  // Show when session exists, not when hasMessages
+            ? [
+                { name: 'undo', description: 'Undo the last message', isBuiltIn: true },
+                { name: 'redo', description: 'Redo previously undone messages', isBuiltIn: true },
+                { name: 'timeline', description: 'Jump to a specific message', isBuiltIn: true },
+              ]
+            : []
+          ),
           { name: 'summarize', description: 'Generate a summary of the current session', isBuiltIn: true },
         ];
 
@@ -134,7 +154,7 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
     };
 
     loadCommands();
-  }, [searchQuery, hasMessagesInCurrentSession]);
+  }, [searchQuery, hasMessagesInCurrentSession, hasSession]);
 
   React.useEffect(() => {
     setSelectedIndex(0);
@@ -184,6 +204,12 @@ export const CommandAutocomplete = React.forwardRef<CommandAutocompleteHandle, C
     switch (command.name) {
       case 'init':
         return <RiFileLine className="h-3.5 w-3.5 text-green-500" />;
+      case 'undo':
+        return <RiArrowGoBackLine className="h-3.5 w-3.5 text-orange-500" />;
+      case 'redo':
+        return <RiArrowGoForwardLine className="h-3.5 w-3.5 text-orange-500" />;
+      case 'timeline':
+        return <RiTimeLine className="h-3.5 w-3.5 text-blue-500" />;
       case 'summarize':
         return <RiScissorsLine className="h-3.5 w-3.5 text-purple-500" />;
       case 'test':

packages/ui/src/components/chat/TimelineDialog.tsx

@@ -0,0 +1,202 @@
+import React from 'react';
+import {
+    Dialog,
+    DialogContent,
+    DialogDescription,
+    DialogHeader,
+    DialogTitle,
+} from '@/components/ui/dialog';
+import { Button } from '@/components/ui/button';
+import { Input } from '@/components/ui/input';
+import { useSessionStore } from '@/stores/useSessionStore';
+import { useMessageStore } from '@/stores/messageStore';
+import { cn } from '@/lib/utils';
+import { RiLoader4Line, RiSearchLine, RiTimeLine, RiGitBranchLine } from '@remixicon/react';
+import type { Part } from '@opencode-ai/sdk';
+
+interface TimelineDialogProps {
+    open: boolean;
+    onOpenChange: (open: boolean) => void;
+    onScrollToMessage?: (messageId: string) => void;
+}
+
+// Helper: format relative time (e.g., "2 hours ago")
+function formatRelativeTime(timestamp: number): string {
+    const now = Date.now();
+    const diffMs = now - timestamp;
+    const diffSecs = Math.floor(diffMs / 1000);
+    const diffMins = Math.floor(diffSecs / 60);
+    const diffHours = Math.floor(diffMins / 60);
+    const diffDays = Math.floor(diffHours / 24);
+
+    if (diffSecs < 60) return 'just now';
+    if (diffMins < 60) return `${diffMins}m ago`;
+    if (diffHours < 24) return `${diffHours}h ago`;
+    if (diffDays < 7) return `${diffDays}d ago`;
+    return new Date(timestamp).toLocaleDateString();
+}
+
+export const TimelineDialog: React.FC<TimelineDialogProps> = ({ open, onOpenChange, onScrollToMessage }) => {
+    const currentSessionId = useSessionStore((state) => state.currentSessionId);
+    const messages = useMessageStore((state) =>
+        currentSessionId ? state.messages.get(currentSessionId) || [] : []
+    );
+    const revertToMessage = useSessionStore((state) => state.revertToMessage);
+    const forkFromMessage = useSessionStore((state) => state.forkFromMessage);
+    const loadSessions = useSessionStore((state) => state.loadSessions);
+
+    const [forkingMessageId, setForkingMessageId] = React.useState<string | null>(null);
+    const [searchQuery, setSearchQuery] = React.useState('');
+
+    // Filter user messages (reversed for newest first)
+    const userMessages = React.useMemo(() => {
+        const filtered = messages.filter(m => m.info.role === 'user');
+        return filtered.reverse();
+    }, [messages]);
+
+    // Filter by search query
+    const filteredMessages = React.useMemo(() => {
+        if (!searchQuery.trim()) return userMessages;
+
+        const query = searchQuery.toLowerCase();
+        return userMessages.filter((message) => {
+            const preview = getMessagePreview(message.parts).toLowerCase();
+            return preview.includes(query);
+        });
+    }, [userMessages, searchQuery]);
+
+    // Handle fork with loading state and session refresh
+    const handleFork = async (messageId: string) => {
+        if (!currentSessionId) return;
+        setForkingMessageId(messageId);
+        try {
+            await forkFromMessage(currentSessionId, messageId);
+            await loadSessions();
+            onOpenChange(false);
+        } finally {
+            setForkingMessageId(null);
+        }
+    };
+
+    if (!currentSessionId) return null;
+
+    return (
+        <Dialog open={open} onOpenChange={onOpenChange}>
+            <DialogContent className="max-w-2xl max-h-[70vh] flex flex-col">
+                <DialogHeader>
+                    <DialogTitle className="flex items-center gap-2">
+                        <RiTimeLine className="h-5 w-5" />
+                        Conversation Timeline
+                    </DialogTitle>
+                    <DialogDescription>
+                        Navigate to any point in the conversation or fork a new session
+                    </DialogDescription>
+                </DialogHeader>
+
+                <div className="flex items-center gap-2 mt-2">
+                    <RiSearchLine className="h-4 w-4 text-muted-foreground" />
+                    <Input
+                        placeholder="Search messages..."
+                        value={searchQuery}
+                        onChange={(e) => setSearchQuery(e.target.value)}
+                        className="flex-1"
+                    />
+                </div>
+
+                <div className="flex-1 overflow-y-auto space-y-2">
+                    {filteredMessages.length === 0 ? (
+                        <div className="text-center text-muted-foreground py-8">
+                            {searchQuery ? 'No messages found' : 'No messages in this session yet'}
+                        </div>
+                    ) : (
+                        filteredMessages.map((message) => {
+                            const preview = getMessagePreview(message.parts);
+                            const timestamp = message.info.time.created;
+                            const relativeTime = formatRelativeTime(timestamp);
+
+                            return (
+                                <div
+                                    key={message.info.id}
+                                    className={cn(
+                                        "group flex items-start gap-3 p-3 rounded-lg border transition-all",
+                                        "hover:border-primary/50 hover:bg-muted/30"
+                                    )}
+                                >
+                                    <div className="flex-1 min-w-0">
+                                        <div className="flex items-center gap-2">
+                                            <span className="typography-meta text-muted-foreground">
+                                                Message {userMessages.length - userMessages.indexOf(message)}
+                                            </span>
+                                            <span className="typography-meta text-muted-foreground">
+                                                •
+                                            </span>
+                                            <span className="typography-meta text-muted-foreground">
+                                                {relativeTime}
+                                            </span>
+                                        </div>
+                                        <p className="typography-small text-foreground mt-1 line-clamp-2">
+                                            {preview || '[No text content]'}
+                                        </p>
+                                    </div>
+
+                                    <div className="flex gap-2 opacity-0 group-hover:opacity-100 transition-opacity">
+                                        <Button
+                                            size="sm"
+                                            variant="outline"
+                                            onClick={() => {
+                                                onScrollToMessage?.(message.info.id);
+                                                onOpenChange(false);
+                                            }}
+                                        >
+                                            Go here
+                                        </Button>
+
+                                        <Button
+                                            size="sm"
+                                            variant="default"
+                                            onClick={async () => {
+                                                await revertToMessage(currentSessionId, message.info.id);
+                                                onOpenChange(false);
+                                            }}
+                                        >
+                                            Revert
+                                        </Button>
+
+                                        <Button
+                                            size="sm"
+                                            variant="secondary"
+                                            onClick={() => handleFork(message.info.id)}
+                                            disabled={forkingMessageId === message.info.id}
+                                        >
+                                            {forkingMessageId === message.info.id ? (
+                                                <RiLoader4Line className="h-4 w-4 animate-spin" />
+                                            ) : 'Fork'}
+                                        </Button>
+                                    </div>
+                                </div>
+                            );
+                        })
+                    )}
+                </div>
+
+                <div className="mt-4 p-3 bg-muted/30 rounded-lg">
+                    <div className="flex items-start gap-2 typography-meta text-muted-foreground">
+                        <RiGitBranchLine className="h-4 w-4 mt-0.5" />
+                        <div>
+                            <p className="font-medium mb-1">Actions</p>
+                            <p>• <strong>Go here</strong> - Scroll to this message in the conversation</p>
+                            <p>• <strong>Revert</strong> - Undo to this point (message text will populate input)</p>
+                            <p>• <strong>Fork</strong> - Create a new session starting from here</p>
+                        </div>
+                    </div>
+                </div>
+            </DialogContent>
+        </Dialog>
+    );
+};
+
+function getMessagePreview(parts: Part[]): string {
+    const textPart = parts.find(p => p.type === 'text');
+    if (!textPart || typeof textPart.text !== 'string') return '';
+    return textPart.text.replace(/\n/g, ' ').slice(0, 80);
+}

packages/ui/src/components/chat/message/MessageBody.tsx

@@ -16,7 +16,7 @@ import { isEmptyTextPart, extractTextContent } from './partUtils';
 import { FadeInOnReveal } from './FadeInOnReveal';
 import { Button } from '@/components/ui/button';
 import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip';
-import { RiCheckLine, RiFileCopyLine, RiChatNewLine, RiArrowGoBackLine } from '@remixicon/react';
+import { RiCheckLine, RiFileCopyLine, RiChatNewLine, RiArrowGoBackLine, RiGitBranchLine } from '@remixicon/react';
 import { ArrowsMerge } from '@/components/icons/ArrowsMerge';
 import type { ContentChangeReason } from '@/hooks/useChatScrollManager';
 
@@ -133,6 +133,7 @@ interface MessageBodyProps {
     agentMention?: AgentMentionInfo;
     turnGroupingContext?: TurnGroupingContext;
     onRevert?: () => void;
+    onFork?: () => void;
     errorMessage?: string;
 }
 
@@ -147,7 +148,8 @@ const UserMessageBody: React.FC<{
     onShowPopup: (content: ToolPopupContent) => void;
     agentMention?: AgentMentionInfo;
     onRevert?: () => void;
-}> = ({ messageId, parts, isMobile, hasTouchInput, hasTextContent, onCopyMessage, copiedMessage, onShowPopup, agentMention, onRevert }) => {
+    onFork?: () => void;
+}> = ({ messageId, parts, isMobile, hasTouchInput, hasTextContent, onCopyMessage, copiedMessage, onShowPopup, agentMention, onRevert, onFork }) => {
     const [copyHintVisible, setCopyHintVisible] = React.useState(false);
     const copyHintTimeoutRef = React.useRef<number | null>(null);
 
@@ -239,7 +241,7 @@ const UserMessageBody: React.FC<{
                 })}
             </div>
             <MessageFilesDisplay files={parts} onShowPopup={onShowPopup} />
-            {(canCopyMessage && hasCopyableText) || onRevert ? (
+            {(canCopyMessage && hasCopyableText) || onRevert || onFork ? (
                 <div className={cn(
                     "mt-1 flex items-center justify-end gap-2 opacity-0 pointer-events-none transition-opacity duration-150 group-hover/message:opacity-100 group-hover/message:pointer-events-auto focus-within:opacity-100 focus-within:pointer-events-auto",
                     copyHintVisible && "opacity-100 pointer-events-auto"
@@ -265,6 +267,26 @@ const UserMessageBody: React.FC<{
                             <TooltipContent sideOffset={6}>Revert from here</TooltipContent>
                         </Tooltip>
                     )}
+                    {onFork && (
+                        <Tooltip delayDuration={1000}>
+                            <TooltipTrigger asChild>
+                                <Button
+                                    type="button"
+                                    variant="ghost"
+                                    size="icon"
+                                    className="h-8 w-8 text-muted-foreground bg-transparent hover:text-foreground hover:!bg-transparent active:!bg-transparent focus-visible:!bg-transparent focus-visible:ring-2 focus-visible:ring-primary/50"
+                                    onPointerDown={(event) => event.stopPropagation()}
+                                    onClick={(event) => {
+                                        event.stopPropagation();
+                                        onFork();
+                                    }}
+                                >
+                                    <RiGitBranchLine className="h-3.5 w-3.5" />
+                                </Button>
+                            </TooltipTrigger>
+                            <TooltipContent sideOffset={6}>Fork from here</TooltipContent>
+                        </Tooltip>
+                    )}
                     {canCopyMessage && hasCopyableText && (
                         <Tooltip delayDuration={1000}>
                             <TooltipTrigger asChild>
@@ -1226,6 +1248,7 @@ const MessageBody: React.FC<MessageBodyProps> = ({ isUser, ...props }) => {
                 onShowPopup={props.onShowPopup}
                 agentMention={props.agentMention}
                 onRevert={props.onRevert}
+                onFork={props.onFork}
             />
         );
     }

packages/ui/src/lib/opencode/client.ts

@@ -664,6 +664,28 @@ class OpencodeService {
     return response.data;
   }
 
+  async forkSession(sessionId: string, messageId?: string): Promise<Session> {
+    const baseUrl = this.baseUrl.replace(/\/$/, '');
+    const url = new URL(`/api/session/${sessionId}/fork`, baseUrl);
+
+    if (this.currentDirectory) {
+      url.searchParams.set('directory', this.currentDirectory);
+    }
+
+    const response = await fetch(url.toString(), {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(messageId ? { messageID: messageId } : {}),
+    });
+
+    if (!response.ok) {
+      const text = await response.text();
+      throw new Error(`Failed to fork session: ${text || response.statusText}`);
+    }
+
+    return response.json();
+  }
+
   async getSessionStatus(): Promise<
     Record<string, { type: "idle" | "busy" | "retry"; attempt?: number; message?: string; next?: number }>
   > {

packages/ui/src/stores/types/sessionTypes.ts

@@ -192,6 +192,9 @@ export interface SessionStore {
      updateSession: (session: Session) => void;
 
      revertToMessage: (sessionId: string, messageId: string) => Promise<void>;
+     handleSlashUndo: (sessionId: string) => Promise<void>;
+     handleSlashRedo: (sessionId: string) => Promise<void>;
+     forkFromMessage: (sessionId: string, messageId: string) => Promise<void>;
      setPendingInputText: (text: string | null) => void;
      consumePendingInputText: () => string | null;
  }

packages/ui/src/stores/useSessionStore.ts

@@ -553,6 +553,139 @@ export const useSessionStore = create<SessionStore>()(
                     }
                 },
 
+                handleSlashUndo: async (sessionId: string) => {
+                    const messages = get().messages.get(sessionId) || [];
+                    const userMessages = messages.filter(m => m.info.role === 'user');
+                    const sessions = get().sessions;
+                    const currentSession = sessions.find(s => s.id === sessionId);
+
+                    // Silent no-op like OpenCode CLI
+                    if (userMessages.length === 0) {
+                        return;
+                    }
+
+                    // Get current revert state to determine which message to undo next
+                    const revertToId = currentSession?.revert?.messageID;
+
+                    // Find the user message AFTER the revert point (or last message if no revert)
+                    let targetMessage;
+                    if (revertToId) {
+                        const revertIndex = userMessages.findIndex(m => m.info.id === revertToId);
+                        targetMessage = userMessages[revertIndex + 1];
+                    } else {
+                        targetMessage = userMessages[userMessages.length - 1];
+                    }
+
+                    // Silent no-op like OpenCode CLI
+                    if (!targetMessage) {
+                        return;
+                    }
+
+                    // Helper to extract text preview
+                    const textPart = targetMessage.parts.find(p => p.type === 'text');
+                    const preview = typeof textPart === 'object' && textPart && 'text' in textPart
+                        ? String(textPart.text).slice(0, 50) + (String(textPart.text).length > 50 ? '...' : '')
+                        : '[No text]';
+
+                    await get().revertToMessage(sessionId, targetMessage.info.id);
+
+                    const { toast } = await import('sonner');
+                    toast.success(`Undid to: ${preview}`);
+                },
+
+                handleSlashRedo: async (sessionId: string) => {
+                    const sessions = get().sessions;
+                    const currentSession = sessions.find(s => s.id === sessionId);
+                    const revertToId = currentSession?.revert?.messageID;
+
+                    // Silent no-op like OpenCode CLI
+                    if (!revertToId) {
+                        return;
+                    }
+
+                    const messages = get().messages.get(sessionId) || [];
+                    const userMessages = messages.filter(m => m.info.role === 'user');
+
+                    // Find the user message BEFORE the revert point
+                    const revertIndex = userMessages.findIndex(m => m.info.id === revertToId);
+                    const targetMessage = userMessages[revertIndex - 1];
+
+                    if (targetMessage) {
+                        // Partial redo: move to previous message
+                        const textPart = targetMessage.parts.find(p => p.type === 'text');
+                        const preview = typeof textPart === 'object' && textPart && 'text' in textPart
+                            ? String(textPart.text).slice(0, 50) + (String(textPart.text).length > 50 ? '...' : '')
+                            : '[No text]';
+
+                        await get().revertToMessage(sessionId, targetMessage.info.id);
+
+                        const { toast } = await import('sonner');
+                        toast.success(`Redid to: ${preview}`);
+                    } else {
+                        // Full unrevert: restore all
+                        const session = await opencodeClient.unrevertSession(sessionId);
+                        await useSessionManagementStore.getState().updateSession(session);
+                        await get().loadMessages(sessionId);
+
+                        const { toast } = await import('sonner');
+                        toast.success('Restored all messages');
+                    }
+                },
+
+                forkFromMessage: async (sessionId: string, messageId: string) => {
+                    const sessions = get().sessions;
+                    const existingSession = sessions.find(s => s.id === sessionId);
+                    if (!existingSession) return;
+
+                    try {
+                        // 1. Call SDK fork - backend copies all messages up to messageId
+                        const result = await opencodeClient.forkSession(sessionId, messageId);
+
+                        if (!result || !result.id) {
+                            const { toast } = await import('sonner');
+                            toast.error('Failed to fork session');
+                            return;
+                        }
+
+                        // 2. Extract fork point content for input field (text + file attachments)
+                        const messages = get().messages.get(sessionId) || [];
+                        const message = messages.find(m => m.info.id === messageId);
+
+                        if (!message) {
+                            const { toast } = await import('sonner');
+                            toast.error('Message not found');
+                            return;
+                        }
+
+                        // Extract text content from non-synthetic, non-ignored text parts
+                        let inputText = '';
+                        for (const part of message.parts) {
+                            if (part.type === 'text' && !part.synthetic && !part.ignored) {
+                                const typedPart = part as { text?: string };
+                                inputText += typedPart.text || '';
+                            }
+                        }
+
+                        // 3. Switch to new session
+                        get().setCurrentSession(result.id);
+
+                        // 4. Show fork point as pending input (will populate ChatInput)
+                        if (inputText) {
+                            set({ pendingInputText: inputText });
+                        }
+
+                        // Load the new session's messages
+                        await get().loadMessages(result.id);
+
+                        const { toast } = await import('sonner');
+                        toast.success(`Forked from ${existingSession.title}`);
+                    } catch (error) {
+                        console.error('Failed to fork session:', error);
+                        const { toast } = await import('sonner');
+                        toast.error('Failed to fork session');
+                    }
+                },
+
                 setPendingInputText: (text: string | null) => {
                     set({ pendingInputText: text });
                 },

packages/ui/src/stores/useUIStore.ts

@@ -52,6 +52,7 @@ interface UIStore {
   diffLayoutPreference: 'dynamic' | 'inline' | 'side-by-side';
   diffFileLayout: Record<string, 'inline' | 'side-by-side'>;
   diffWrapLines: boolean;
+  isTimelineDialogOpen: boolean;
 
   setTheme: (theme: 'light' | 'dark' | 'system') => void;
   toggleSidebar: () => void;
@@ -93,6 +94,7 @@ interface UIStore {
   setDiffFileLayout: (filePath: string, mode: 'inline' | 'side-by-side') => void;
   setDiffWrapLines: (wrap: boolean) => void;
   setMultiRunLauncherOpen: (open: boolean) => void;
+  setTimelineDialogOpen: (open: boolean) => void;
   openMultiRunLauncher: () => void;
   openMultiRunLauncherWithPrompt: (prompt: string) => void;
 }
@@ -135,6 +137,7 @@ export const useUIStore = create<UIStore>()(
         diffLayoutPreference: 'dynamic',
         diffFileLayout: {},
         diffWrapLines: false,
+        isTimelineDialogOpen: false,
 
         setTheme: (theme) => {
           set({ theme });
@@ -458,6 +461,10 @@ export const useUIStore = create<UIStore>()(
             isSessionSwitcherOpen: false,
           });
         },
+
+        setTimelineDialogOpen: (open) => {
+          set({ isTimelineDialogOpen: open });
+        },
       }),
       {
         name: 'ui-store',

packages/web/package.json

@@ -43,6 +43,7 @@
     "cmdk": "^1.1.1",
     "express": "^5.1.0",
     "http-proxy-middleware": "^3.0.5",
+    "jsonc-parser": "^3.3.1",
     "next-themes": "^0.4.6",
     "bun-pty": "^0.4.5",
     "node-pty": "^1.1.0",

packages/web/server/lib/opencode-config.js

@@ -2,7 +2,7 @@ import fs from 'fs';
 import path from 'path';
 import os from 'os';
 import yaml from 'yaml';
-import stripJsonComments from 'strip-json-comments';
+import { parse as parseJsonc } from 'jsonc-parser';
 
 const OPENCODE_CONFIG_DIR = path.join(os.homedir(), '.config', 'opencode');
 const AGENT_DIR = path.join(OPENCODE_CONFIG_DIR, 'agent');
@@ -431,11 +431,12 @@ function readConfigFile(filePath) {
   }
   try {
     const content = fs.readFileSync(filePath, 'utf8');
-    const normalized = stripJsonComments(content).trim();
+    const normalized = content.trim();
     if (!normalized) {
       return {};
     }
-    return JSON.parse(normalized);
+    // jsonc-parser handles comments, trailing commas, unquoted keys
+    return parseJsonc(normalized, [], { allowTrailingComma: true });
   } catch (error) {
     console.error(`Failed to read config file: ${filePath}`, error);
     throw new Error('Failed to read OpenCode configuration');