feat: add fork assistant message to new session

Add fork button on assistant messages to start new execution session
Include synthetic meta-instruction when forking to explain context

packages/ui/src/stores/messageStore.ts

@@ -3,6 +3,7 @@ import { create } from "zustand";
 import { devtools, persist, createJSONStorage } from "zustand/middleware";
 import type { Message, Part } from "@opencode-ai/sdk";
 import { opencodeClient } from "@/lib/opencode/client";
+import { isExecutionForkMetaText } from "@/lib/messages/executionMeta";
 import type { SessionMemoryState, MessageStreamLifecycle, AttachedFile } from "./types/sessionTypes";
 import { MEMORY_LIMITS } from "./types/sessionTypes";
 import {
@@ -332,7 +333,15 @@ export const useMessageStore = create<MessageStore>()(
                                     userMessageMarker: message.info.role === "user" ? true : (message.info as any)?.userMessageMarker,
                                 } as any;
 
-                                const serverParts = Array.isArray(message.parts) ? [...message.parts] : [];
+                                const serverParts = (Array.isArray(message.parts) ? message.parts : []).map((part) => {
+                                    if (part?.type === 'text') {
+                                        const raw = (part as any).text ?? (part as any).content ?? '';
+                                        if (isExecutionForkMetaText(raw)) {
+                                            return { ...part, synthetic: true } as Part;
+                                        }
+                                    }
+                                    return part;
+                                });
                                 const existingEntry = infoWithMarker?.id
                                     ? previousMessagesById.get(infoWithMarker.id as string)
                                     : undefined;
@@ -935,6 +944,9 @@ export const useMessageStore = create<MessageStore>()(
                         }
 
                     const incomingText = extractTextFromPart(part);
+                    if (isExecutionForkMetaText(incomingText)) {
+                        (part as any).synthetic = true;
+                    }
                     if (streamDebugEnabled() && actualRole === "assistant") {
                         try {
                             console.info("[STREAM-TRACE] part", {
@@ -1789,7 +1801,15 @@ export const useMessageStore = create<MessageStore>()(
                                         : (message.info as any)?.animationSettled,
                             } as any;
 
-                            const serverParts = Array.isArray(message.parts) ? [...message.parts] : [];
+                            const serverParts = (Array.isArray(message.parts) ? message.parts : []).map((part) => {
+                                if (part?.type === 'text') {
+                                    const raw = (part as any).text ?? (part as any).content ?? '';
+                                    if (isExecutionForkMetaText(raw)) {
+                                        return { ...part, synthetic: true } as Part;
+                                    }
+                                }
+                                return part;
+                            });
                             const messageId = typeof infoWithMarker?.id === "string" ? (infoWithMarker.id as string) : undefined;
                             const existingEntry = messageId ? previousMessagesById.get(messageId) : undefined;
 

packages/ui/src/stores/sessionStore.ts

@@ -21,7 +21,7 @@ interface SessionState {
 
 interface SessionActions {
     loadSessions: () => Promise<void>;
-    createSession: (title?: string, directoryOverride?: string | null) => Promise<Session | null>;
+    createSession: (title?: string, directoryOverride?: string | null, parentID?: string | null) => Promise<Session | null>;
     deleteSession: (id: string, options?: { archiveWorktree?: boolean; deleteRemoteBranch?: boolean; remoteName?: string }) => Promise<boolean>;
     deleteSessions: (ids: string[], options?: { archiveWorktree?: boolean; deleteRemoteBranch?: boolean; remoteName?: string }) => Promise<{ deletedIds: string[]; failedIds: string[] }>;
     updateSessionTitle: (id: string, title: string) => Promise<void>;
@@ -449,7 +449,7 @@ export const useSessionStore = create<SessionStore>()(
                     }
                 },
 
-                createSession: async (title?: string, directoryOverride?: string | null) => {
+                createSession: async (title?: string, directoryOverride?: string | null, parentID?: string | null) => {
                     set({ error: null });
                     const directoryStore = useDirectoryStore.getState();
                     const fallbackDirectory = normalizePath(directoryStore.currentDirectory);
@@ -461,7 +461,7 @@ export const useSessionStore = create<SessionStore>()(
                     const optimisticSession: Session = {
                         id: tempId,
                         title: title || "New session",
-                        parentID: undefined,
+                        parentID: parentID ?? undefined,
                         directory: targetDirectory ?? null,
                         projectID: (previousState.sessions[0] as { projectID?: string })?.projectID ?? "",
                         version: "0.0.0",
@@ -529,7 +529,7 @@ export const useSessionStore = create<SessionStore>()(
                     };
 
                     try {
-                        const createRequest = () => opencodeClient.createSession({ title });
+                        const createRequest = () => opencodeClient.createSession({ title, parentID: parentID ?? undefined });
                         let session: Session | null = null;
 
                         try {

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

@@ -100,7 +100,8 @@ export interface SessionStore {
     toggleSessionAgentEditMode: (sessionId: string, agentName: string | undefined, defaultMode?: EditPermissionMode) => void;
     setSessionAgentEditMode: (sessionId: string, agentName: string | undefined, mode: EditPermissionMode, defaultMode?: EditPermissionMode) => void;
     loadSessions: () => Promise<void>;
-    createSession: (title?: string, directoryOverride?: string | null) => Promise<Session | null>;
+    createSession: (title?: string, directoryOverride?: string | null, parentID?: string | null) => Promise<Session | null>;
+    createSessionFromAssistantMessage: (sourceMessageId: string) => Promise<void>;
 
     deleteSession: (id: string, options?: { archiveWorktree?: boolean; deleteRemoteBranch?: boolean; remoteName?: string }) => Promise<boolean>;
     deleteSessions: (ids: string[], options?: { archiveWorktree?: boolean; deleteRemoteBranch?: boolean; remoteName?: string }) => Promise<{ deletedIds: string[]; failedIds: string[] }>;

packages/ui/src/stores/useSessionStore.ts

@@ -13,6 +13,9 @@ import { useContextStore } from "./contextStore";
 import { usePermissionStore } from "./permissionStore";
 import { opencodeClient } from "@/lib/opencode/client";
 import { useDirectoryStore } from "./useDirectoryStore";
+import { useConfigStore } from "./useConfigStore";
+import { EXECUTION_FORK_META_TEXT } from "@/lib/messages/executionMeta";
+import { flattenAssistantTextParts } from "@/lib/messages/messageText";
 
 export type { AttachedFile, EditPermissionMode };
 export { MEMORY_LIMITS, ACTIVE_SESSION_WINDOW } from "./types/sessionTypes";
@@ -105,14 +108,70 @@ export const useSessionStore = create<SessionStore>()(
                 },
 
                 loadSessions: () => useSessionManagementStore.getState().loadSessions(),
-                createSession: async (title?: string, directoryOverride?: string | null) => {
-                    const result = await useSessionManagementStore.getState().createSession(title, directoryOverride);
+                createSession: async (title?: string, directoryOverride?: string | null, parentID?: string | null) => {
+                    const result = await useSessionManagementStore.getState().createSession(title, directoryOverride, parentID);
 
                     if (result?.id) {
                         await get().setCurrentSession(result.id);
                     }
                     return result;
                 },
+                createSessionFromAssistantMessage: async (sourceMessageId: string) => {
+                    if (!sourceMessageId) {
+                        return;
+                    }
+
+                    const messageStore = useMessageStore.getState();
+                    const { messages, lastUsedProvider } = messageStore;
+                    let sourceEntry: { info: Message; parts: Part[] } | undefined;
+                    let sourceSessionId: string | undefined;
+
+                    messages.forEach((messageList, sessionId) => {
+                        const found = messageList.find((entry) => entry.info?.id === sourceMessageId);
+                        if (found && !sourceEntry) {
+                            sourceEntry = found;
+                            sourceSessionId = sessionId;
+                        }
+                    });
+
+                    if (!sourceEntry || sourceEntry.info.role !== "assistant") {
+                        return;
+                    }
+
+                    const assistantPlanText = flattenAssistantTextParts(sourceEntry.parts);
+                    if (!assistantPlanText.trim()) {
+                        return;
+                    }
+
+                    const sessionManagementStore = useSessionManagementStore.getState();
+                    const directory = resolveSessionDirectory(
+                        sessionManagementStore.sessions,
+                        sourceSessionId ?? null,
+                        sessionManagementStore.getWorktreeMetadata,
+                    );
+
+                    const session = await get().createSession(undefined, directory ?? null, null);
+                    if (!session) {
+                        return;
+                    }
+
+                    const { currentProviderId, currentModelId, currentAgentName } = useConfigStore.getState();
+                    const providerID = currentProviderId || lastUsedProvider?.providerID;
+                    const modelID = currentModelId || lastUsedProvider?.modelID;
+
+                    if (!providerID || !modelID) {
+                        return;
+                    }
+
+                    await opencodeClient.sendMessage({
+                        id: session.id,
+                        providerID,
+                        modelID,
+                        text: assistantPlanText,
+                        prefaceText: EXECUTION_FORK_META_TEXT,
+                        agent: currentAgentName ?? undefined,
+                    });
+                },
                 deleteSession: (id: string, options) => useSessionManagementStore.getState().deleteSession(id, options),
                 deleteSessions: (ids: string[], options) => useSessionManagementStore.getState().deleteSessions(ids, options),
                 updateSessionTitle: (id: string, title: string) => useSessionManagementStore.getState().updateSessionTitle(id, title),