refactor: Drop ThreadWithTasks (#142)

* refactor: Drop ThreadWithTasks

* cr

apps/open-swe/src/nodes/diagnose-error.ts

@@ -19,7 +19,7 @@ import {
   getCompletedPlanItems,
   getCurrentPlanItem,
 } from "../utils/current-task.js";
-import { getActivePlanItems } from "../utils/task-plan.js";
+import { getActivePlanItems } from "@open-swe/shared/open-swe/tasks";
 
 const logger = createLogger(LogLevel.INFO, "DiagnoseError");
 

apps/open-swe/src/nodes/generate-conclusion.ts

@@ -13,7 +13,7 @@ import {
   completeTask,
   getActivePlanItems,
   getActiveTask,
-} from "../utils/task-plan.js";
+} from "@open-swe/shared/open-swe/tasks";
 
 const logger = createLogger(LogLevel.INFO, "GenerateConclusionNode");
 

apps/open-swe/src/nodes/generate-message.ts

@@ -16,7 +16,7 @@ import { stopSandbox } from "../utils/sandbox.js";
 import { createLogger, LogLevel } from "../utils/logger.js";
 import { getCurrentPlanItem } from "../utils/current-task.js";
 import { getMessageContentString } from "@open-swe/shared/messages";
-import { getActivePlanItems } from "../utils/task-plan.js";
+import { getActivePlanItems } from "@open-swe/shared/open-swe/tasks";
 import { SANDBOX_ROOT_DIR } from "@open-swe/shared/constants";
 
 const logger = createLogger(LogLevel.INFO, "GenerateMessageNode");

apps/open-swe/src/nodes/interrupt-plan.ts

@@ -6,7 +6,7 @@ import {
   HumanResponse,
 } from "@langchain/langgraph/prebuilt";
 import { startSandbox } from "../utils/sandbox.js";
-import { createNewTask } from "../utils/task-plan.js";
+import { createNewTask } from "@open-swe/shared/open-swe/tasks";
 import { getUserRequest } from "../utils/user-request.js";
 import {
   PLAN_INTERRUPT_ACTION_TITLE,

apps/open-swe/src/nodes/open-pr.ts

@@ -19,7 +19,7 @@ import { getUserRequest } from "../utils/user-request.js";
 import { ToolMessage } from "@langchain/core/messages";
 import { daytonaClient, deleteSandbox } from "../utils/sandbox.js";
 import { getGitHubTokensFromConfig } from "../utils/github-tokens.js";
-import { getActivePlanItems } from "../utils/task-plan.js";
+import { getActivePlanItems } from "@open-swe/shared/open-swe/tasks";
 
 const logger = createLogger(LogLevel.INFO, "Open PR");
 

apps/open-swe/src/nodes/progress-plan-step.ts

@@ -16,7 +16,7 @@ import {
   completePlanItem,
   getActivePlanItems,
   getActiveTask,
-} from "../utils/task-plan.js";
+} from "@open-swe/shared/open-swe/tasks";
 import {
   getCurrentPlanItem,
   getRemainingPlanItems,

apps/open-swe/src/nodes/summarize-task-steps.ts

@@ -19,7 +19,7 @@ import {
   completePlanItem,
   getActivePlanItems,
   getActiveTask,
-} from "../utils/task-plan.js";
+} from "@open-swe/shared/open-swe/tasks";
 import { getCompletedPlanItems } from "../utils/current-task.js";
 
 const taskSummarySysPrompt = `You are operating as a terminal-based agentic coding assistant built by LangChain. It wraps LLM models to enable natural language interaction with a local codebase. You are expected to be precise, safe, and helpful.

apps/open-swe/src/nodes/update-plan.ts

@@ -6,7 +6,10 @@ import {
 } from "@open-swe/shared/open-swe/types";
 import { loadModel, Task } from "../utils/load-model.js";
 import { z } from "zod";
-import { getActiveTask, updateTaskPlanItems } from "../utils/task-plan.js";
+import {
+  getActiveTask,
+  updateTaskPlanItems,
+} from "@open-swe/shared/open-swe/tasks";
 import {
   BaseMessage,
   isAIMessage,

apps/web/src/components/task-list-sidebar.tsx

@@ -6,10 +6,12 @@ import {
   PanelRightOpen,
 } from "lucide-react";
 import { Button } from "@/components/ui/button";
-import { useThreads, ThreadWithTasks } from "@/providers/Thread";
+import { useThreads } from "@/providers/Thread";
 import { useQueryState, parseAsString } from "nuqs";
 import { useState, useCallback } from "react";
 import { ThreadItem } from "./thread-item";
+import { Thread } from "@langchain/langgraph-sdk";
+import { GraphState } from "@open-swe/shared/open-swe/types";
 
 const THREADS_PER_PAGE = 10;
 
@@ -18,13 +20,12 @@ interface TaskListSidebarProps {
 }
 
 export default function TaskListSidebar({ onCollapse }: TaskListSidebarProps) {
-  const [taskId, setTaskId] = useQueryState("taskId", parseAsString);
   const [threadId, setThreadId] = useQueryState("threadId", parseAsString);
   const [currentPage, setCurrentPage] = useState(0);
   const { threads, threadsLoading, handleThreadClick } = useThreads();
 
   const onThreadClick = useCallback(
-    (thread: ThreadWithTasks) => {
+    (thread: Thread<GraphState>) => {
       handleThreadClick(thread, threadId, setThreadId);
     },
     [handleThreadClick, threadId, setThreadId],

apps/web/src/components/task-list.tsx

@@ -1,10 +1,12 @@
 "use client";
 import { Archive, ChevronLeft, ChevronRight } from "lucide-react";
 import { Button } from "@/components/ui/button";
-import { useThreads, ThreadWithTasks } from "@/providers/Thread";
+import { useThreads } from "@/providers/Thread";
 import { useQueryState, parseAsString } from "nuqs";
 import { useState, useCallback } from "react";
 import { ThreadItem } from "./thread-item";
+import { Thread } from "@langchain/langgraph-sdk";
+import { GraphState } from "@open-swe/shared/open-swe/types";
 
 const THREADS_PER_PAGE = 5;
 
@@ -17,7 +19,7 @@ export default function TaskList() {
   const isDashboardMode = !taskId;
 
   const onThreadClick = useCallback(
-    (thread: ThreadWithTasks) => {
+    (thread: Thread<GraphState>) => {
       handleThreadClick(thread, threadId, setThreadId);
       setTaskId(null);
     },

apps/web/src/components/thread-item.tsx

@@ -1,21 +1,19 @@
 "use client";
 import { memo } from "react";
-import {
-  formatDistanceToNow,
-  differenceInHours,
-  differenceInMinutes,
-  format,
-} from "date-fns";
+import { differenceInHours, differenceInMinutes, format } from "date-fns";
 import { GitBranch, ArrowRight, ListTodo } from "lucide-react";
-import { ThreadWithTasks, useThreads } from "@/providers/Thread";
+import { useThreads } from "@/providers/Thread";
 import { cn } from "@/lib/utils";
 import { StatusIndicator } from "@/components/status-indicator";
 import { GitHubSVG } from "./icons/github";
 import { useQueryState } from "nuqs";
+import { Thread } from "@langchain/langgraph-sdk";
+import { GraphState } from "@open-swe/shared/open-swe/types";
+import { getThreadTasks, getThreadTitle } from "@/lib/thread";
 
 interface ThreadItemProps {
-  thread: ThreadWithTasks;
-  onClick: (thread: ThreadWithTasks) => void;
+  thread: Thread<GraphState>;
+  onClick: (thread: Thread<GraphState>) => void;
   variant?: "sidebar" | "dashboard";
   className?: string;
 }
@@ -55,6 +53,8 @@ export const ThreadItem = memo(function ThreadItem({
 
   const displayDate = formatRelativeDate(thread.created_at);
 
+  const { totalTasks, completedTasks } = getThreadTasks(thread);
+
   return (
     <div
       className={cn(
@@ -74,7 +74,7 @@ export const ThreadItem = memo(function ThreadItem({
           <div className="flex w-full items-center gap-1.5">
             <StatusIndicator status={thread.status} />
             <h4 className="w-full truncate text-xs leading-tight font-medium text-gray-900">
-              {thread.threadTitle}
+              {getThreadTitle(thread)}
             </h4>
           </div>
 
@@ -85,10 +85,14 @@ export const ThreadItem = memo(function ThreadItem({
                 height="16"
                 className="flex-shrink-0"
               />
-              <span className="max-w-[90px] truncate">{thread.repository}</span>
+              <span className="max-w-[90px] truncate">
+                {thread.values.targetRepository.repo}
+              </span>
               <span>/</span>
               <GitBranch className="size-2.5 flex-shrink-0" />
-              <span className="max-w-[70px] truncate">{thread.branch}</span>
+              <span className="max-w-[70px] truncate">
+                {thread.values.targetRepository.branch}
+              </span>
             </div>
 
             <span>•</span>
@@ -101,7 +105,7 @@ export const ThreadItem = memo(function ThreadItem({
                 <div className="ml-1 flex items-center gap-1">
                   <ListTodo className="size-4 flex-shrink-0" />
                   <span>
-                    {thread.completedTasksCount}/{thread.totalTasksCount} tasks
+                    {completedTasks}/{totalTasks} tasks
                   </span>
                 </div>
               </>
@@ -111,7 +115,7 @@ export const ThreadItem = memo(function ThreadItem({
             <div className="flex items-center gap-1 text-xs text-gray-500">
               <ListTodo className="size-4 flex-shrink-0" />
               <span>
-                {thread.completedTasksCount}/{thread.totalTasksCount} tasks
+                {completedTasks}/{totalTasks} tasks
               </span>
             </div>
           )}

apps/web/src/hooks/useThreadPolling.ts

@@ -1,12 +1,13 @@
 import { useEffect, useRef } from "react";
 import { ThreadPoller, PollConfig } from "@/lib/polling/thread-poller";
-import { ThreadWithTasks } from "@/providers/Thread";
+import { GraphState } from "@open-swe/shared/open-swe/types";
+import { Thread } from "@langchain/langgraph-sdk";
 
 interface UseThreadPollingProps {
-  threads: ThreadWithTasks[];
-  getThread: (threadId: string) => Promise<ThreadWithTasks | null>;
+  threads: Thread<GraphState>[];
+  getThread: (threadId: string) => Promise<Thread<GraphState> | null>;
   onUpdate: (
-    updatedThreads: ThreadWithTasks[],
+    updatedThreads: Thread<GraphState>[],
     changedThreadIds: string[],
   ) => void;
 

apps/web/src/lib/polling/thread-poller.ts

@@ -1,9 +1,11 @@
-import { ThreadWithTasks } from "@/providers/Thread";
+import { Thread } from "@langchain/langgraph-sdk";
+import { GraphState } from "@open-swe/shared/open-swe/types";
+import { getThreadTasks, getThreadTitle } from "../thread";
 
 export interface PollConfig {
   interval: number;
   onUpdate: (
-    updatedThreads: ThreadWithTasks[],
+    updatedThreads: Thread<GraphState>[],
     changedThreadIds: string[],
   ) => void;
 }
@@ -12,13 +14,13 @@ export class ThreadPoller {
   private config: PollConfig;
   private isPolling: boolean = false;
   private intervalId: NodeJS.Timeout | null = null;
-  private threads: ThreadWithTasks[];
-  private getThreadFn: (threadId: string) => Promise<ThreadWithTasks | null>;
+  private threads: Thread<GraphState>[];
+  private getThreadFn: (threadId: string) => Promise<Thread<GraphState> | null>;
 
   constructor(
     config: PollConfig,
-    threads: ThreadWithTasks[],
-    getThreadFn: (threadId: string) => Promise<ThreadWithTasks | null>,
+    threads: Thread<GraphState>[],
+    getThreadFn: (threadId: string) => Promise<Thread<GraphState> | null>,
   ) {
     this.config = config;
     this.threads = threads;
@@ -49,7 +51,7 @@ export class ThreadPoller {
       const currentThreads = this.threads;
 
       const threadsToPool = currentThreads.slice(0, 10);
-      const updatedThreads: ThreadWithTasks[] = [];
+      const updatedThreads: Thread<GraphState>[] = [];
       const changedThreadIds: string[] = [];
       const errors: string[] = [];
 
@@ -79,19 +81,24 @@ export class ThreadPoller {
   }
 
   private hasThreadChanged(
-    current: ThreadWithTasks,
-    updated: ThreadWithTasks,
+    current: Thread<GraphState>,
+    updated: Thread<GraphState>,
   ): boolean {
+    const currentTaskCounts = getThreadTasks(current);
+    const updatedTaskCounts = getThreadTasks(updated);
+    const currentTargetRepo = current.values?.targetRepository;
+    const updatedTargetRepo = updated.values?.targetRepository;
     return (
-      current.completedTasksCount !== updated.completedTasksCount ||
-      current.totalTasksCount !== updated.totalTasksCount ||
+      currentTaskCounts.completedTasks !== updatedTaskCounts.completedTasks ||
+      currentTaskCounts.totalTasks !== updatedTaskCounts.totalTasks ||
       current.status !== updated.status ||
-      current.threadTitle !== updated.threadTitle ||
-      current.repository !== updated.repository ||
-      current.branch !== updated.branch ||
-      JSON.stringify(current.tasks) !== JSON.stringify(updated.tasks) ||
-      JSON.stringify(current.proposedPlan) !==
-        JSON.stringify(updated.proposedPlan)
+      getThreadTitle(current) !== getThreadTitle(updated) ||
+      currentTargetRepo.repo !== updatedTargetRepo.repo ||
+      currentTargetRepo.branch !== updatedTargetRepo.branch ||
+      JSON.stringify(current.values?.plan) !==
+        JSON.stringify(updated.values?.plan) ||
+      JSON.stringify(current.values?.proposedPlan) !==
+        JSON.stringify(updated.values?.proposedPlan)
     );
   }
 }

apps/web/src/lib/thread.ts

@@ -0,0 +1,32 @@
+import { Thread } from "@langchain/langgraph-sdk";
+import { getMessageContentString } from "@open-swe/shared/messages";
+import { GraphState } from "@open-swe/shared/open-swe/types";
+import { getActivePlanItems } from "@open-swe/shared/open-swe/tasks";
+
+export function getThreadTitle(thread: Thread<GraphState>): string {
+  const messages = thread?.values.messages;
+  if (!messages?.length || !messages[0]?.content) {
+    return `Thread ${thread.thread_id.substring(0, 8)}`;
+  }
+  const threadTitle = getMessageContentString(messages[0].content);
+  return threadTitle;
+}
+
+export function getThreadTasks(thread: Thread<GraphState>): {
+  totalTasks: number;
+  completedTasks: number;
+} {
+  if (!thread.values.plan) {
+    return {
+      totalTasks: 0,
+      completedTasks: 0,
+    };
+  }
+  const activePlanItems = getActivePlanItems(thread.values.plan);
+  const totalTasks = activePlanItems.length;
+  const completedTasks = activePlanItems.filter((p) => p.completed).length;
+  return {
+    totalTasks,
+    completedTasks,
+  };
+}

apps/web/src/providers/Thread.tsx

@@ -12,31 +12,20 @@ import {
   useTransition,
 } from "react";
 import { createClient } from "./client";
-import { getMessageContentString } from "@open-swe/shared/messages";
 import { TaskPlan, GraphState } from "@open-swe/shared/open-swe/types";
 import { useThreadPolling } from "@/hooks/useThreadPolling";
 
-export interface ThreadWithTasks extends Thread {
-  threadTitle: string;
-  repository: string;
-  branch: string;
-  completedTasksCount: number;
-  totalTasksCount: number;
-  tasks: TaskPlan | undefined;
-  proposedPlan: string[];
-}
-
 interface ThreadContextType {
-  threads: ThreadWithTasks[];
-  setThreads: Dispatch<SetStateAction<ThreadWithTasks[]>>;
+  threads: Thread<GraphState>[];
+  setThreads: Dispatch<SetStateAction<Thread<GraphState>[]>>;
   threadsLoading: boolean;
   setThreadsLoading: Dispatch<SetStateAction<boolean>>;
   refreshThreads: () => Promise<void>;
-  getThread: (threadId: string) => Promise<ThreadWithTasks | null>;
+  getThread: (threadId: string) => Promise<Thread<GraphState> | null>;
   isPending: boolean;
   recentlyUpdatedThreads: Set<string>;
   handleThreadClick: (
-    thread: ThreadWithTasks,
+    thread: Thread<GraphState>,
     currentThreadId: string | null,
     setThreadId: (id: string) => void,
   ) => void;
@@ -115,7 +104,7 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
   const assistantId: string | undefined =
     process.env.NEXT_PUBLIC_ASSISTANT_ID ?? "";
 
-  const [threads, setThreads] = useState<ThreadWithTasks[]>([]);
+  const [threads, setThreads] = useState<Thread<GraphState>[]>([]);
   const [threadsLoading, setThreadsLoading] = useState(false);
   const [isPending, startTransition] = useTransition();
   const [recentlyUpdatedThreads, setRecentlyUpdatedThreads] = useState<
@@ -123,23 +112,13 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
   >(new Set());
 
   const getThread = useCallback(
-    async (threadId: string): Promise<ThreadWithTasks | null> => {
+    async (threadId: string): Promise<Thread<GraphState> | null> => {
       if (!apiUrl || !assistantId) return null;
       const client = createClient(apiUrl);
 
       try {
-        const thread = await client.threads.get(threadId);
-
-        // Get the comprehensive state data which contains the plan
-        let stateData: { values: GraphState } | null = null;
-
-        try {
-          stateData = await client.threads.getState(threadId);
-        } catch (stateError) {
-          console.error("Failed to get state data:", stateError);
-        }
-
-        return enhanceThreadWithTasks(thread, stateData);
+        const thread = await client.threads.get<GraphState>(threadId);
+        return thread;
       } catch (error) {
         console.error("Failed to fetch thread:", threadId, error);
         return null;
@@ -148,42 +127,6 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
     [apiUrl, assistantId],
   );
 
-  const enhanceThreadWithTasks = (
-    thread: Thread,
-    stateData?: { values: GraphState } | null,
-  ): ThreadWithTasks => {
-    const stateValues = stateData?.values;
-    const threadValues = thread.values as GraphState;
-
-    const plan: TaskPlan | undefined = stateValues?.plan || threadValues?.plan;
-    const proposedPlan: string[] =
-      stateValues?.proposedPlan || threadValues?.proposedPlan || [];
-
-    const targetRepository =
-      stateValues?.targetRepository || threadValues?.targetRepository;
-    const messages = stateValues?.messages || threadValues?.messages;
-    const firstMessageContent = messages?.[0]?.content;
-    const threadTitle = firstMessageContent
-      ? getMessageContentString(firstMessageContent)
-      : `Thread ${thread.thread_id.substring(0, 8)}`;
-
-    const { totalTasksCount, completedTasksCount } = getTaskCounts(
-      plan,
-      proposedPlan,
-    );
-
-    return {
-      ...thread,
-      threadTitle,
-      repository: targetRepository?.repo || "Unknown Repository",
-      branch: targetRepository?.branch || "main",
-      completedTasksCount,
-      totalTasksCount,
-      tasks: plan,
-      proposedPlan,
-    };
-  };
-
   const refreshThreads = useCallback(async (): Promise<void> => {
     if (!apiUrl || !assistantId) return;
 
@@ -196,42 +139,25 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
         metadata: getThreadSearchMetadata(assistantId),
       };
 
-      let threadsResponse = await client.threads.search(searchParams);
+      let threadsResponse =
+        await client.threads.search<GraphState>(searchParams);
 
       if (threadsResponse.length === 0) {
         const altMetadata = assistantId.includes("-")
           ? { assistant_id: assistantId }
           : { graph_id: assistantId };
-        threadsResponse = await client.threads.search({
+        threadsResponse = await client.threads.search<GraphState>({
           limit: 100,
           metadata: altMetadata,
         });
       }
 
-      const enhancedThreads: ThreadWithTasks[] = [];
-      for (const thread of threadsResponse) {
-        try {
-          const fullThread = await client.threads.get(thread.thread_id);
-
-          let stateData: { values: GraphState } | null = null;
-          try {
-            stateData = await client.threads.getState(thread.thread_id);
-          } catch (stateError) {
-            console.error("Failed to get state data:", stateError);
-          }
-
-          enhancedThreads.push(enhanceThreadWithTasks(fullThread, stateData));
-        } catch (error) {
-          console.error(`Failed to enhance thread ${thread.thread_id}:`, error);
-        }
-      }
-
-      enhancedThreads.sort(
+      threadsResponse.sort(
         (a, b) =>
           new Date(b.created_at).getTime() - new Date(a.created_at).getTime(),
       );
 
-      setThreads(enhancedThreads);
+      setThreads(threadsResponse);
     } catch (error) {
       console.error("Failed to fetch threads:", error);
     } finally {
@@ -244,7 +170,7 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
   }, [refreshThreads]);
 
   const handlePollingUpdate = useCallback(
-    (updatedThreads: ThreadWithTasks[], changedThreadIds: string[]) => {
+    (updatedThreads: Thread<GraphState>[], changedThreadIds: string[]) => {
       setThreads((currentThreads) => {
         const updatedMap = new Map(updatedThreads.map((t) => [t.thread_id, t]));
         return currentThreads.map(
@@ -271,7 +197,7 @@ export function ThreadProvider({ children }: { children: ReactNode }) {
 
   const handleThreadClick = useCallback(
     (
-      thread: ThreadWithTasks,
+      thread: Thread<GraphState>,
       currentThreadId: string | null,
       setThreadId: (id: string) => void,
     ) => {

packages/shared/src/open-swe/tasks.ts

@@ -0,0 +1,274 @@
+import { v4 as uuidv4 } from "uuid";
+import { PlanItem, Task, TaskPlan, PlanRevision } from "./types.js";
+
+/**
+ * Creates a new task with the provided plan items.
+ * Can either add to an existing TaskPlan or create a brand new one.
+ *
+ * @param request The original user request text that initiated this task
+ * @param planItems The plan items to include in the new task
+ * @param existingTaskPlan Optional existing TaskPlan to add the new task to
+ * @param parentTaskId Optional ID of a parent task if this task is derived from another
+ * @returns The updated TaskPlan with the new task added
+ */
+export function createNewTask(
+  request: string,
+  planItems: PlanItem[],
+  existingTaskPlan?: TaskPlan,
+  parentTaskId?: string,
+): TaskPlan {
+  // Create the initial plan revision
+  const initialRevision: PlanRevision = {
+    revisionIndex: 0,
+    plans: planItems,
+    createdAt: Date.now(),
+    createdBy: "agent",
+  };
+
+  // Create the new task
+  const newTask: Task = {
+    id: uuidv4(),
+    taskIndex: existingTaskPlan ? existingTaskPlan.tasks.length : 0,
+    request,
+    createdAt: Date.now(),
+    completed: false,
+    planRevisions: [initialRevision],
+    activeRevisionIndex: 0,
+    parentTaskId,
+  };
+
+  // If there's an existing task plan, add the new task to it
+  if (existingTaskPlan) {
+    return {
+      tasks: [...existingTaskPlan.tasks, newTask],
+      activeTaskIndex: existingTaskPlan.tasks.length, // Set the new task as active
+    };
+  }
+
+  // Otherwise create a new task plan with just this task
+  return {
+    tasks: [newTask],
+    activeTaskIndex: 0,
+  };
+}
+
+/**
+ * Updates the plan items for an existing task by creating a new revision.
+ *
+ * @param taskPlan The current task plan
+ * @param taskId The ID of the task to update
+ * @param planItems The new plan items
+ * @param createdBy Who created this revision ('agent' or 'user')
+ * @returns The updated TaskPlan with the new revision
+ * @throws Error if the task ID doesn't exist
+ */
+export function updateTaskPlanItems(
+  taskPlan: TaskPlan,
+  taskId: string,
+  planItems: PlanItem[],
+  createdBy: "agent" | "user" = "agent",
+): TaskPlan {
+  // Find the task to update
+  const taskIndex = taskPlan.tasks.findIndex((task) => task.id === taskId);
+
+  if (taskIndex === -1) {
+    throw new Error(`Task with ID ${taskId} not found`);
+  }
+
+  const task = taskPlan.tasks[taskIndex];
+
+  // Create a new revision with the updated plan items
+  const newRevision: PlanRevision = {
+    revisionIndex: task.planRevisions.length,
+    plans: planItems,
+    createdAt: Date.now(),
+    createdBy,
+  };
+
+  // Create an updated task with the new revision
+  const updatedTask: Task = {
+    ...task,
+    planRevisions: [...task.planRevisions, newRevision],
+    activeRevisionIndex: task.planRevisions.length, // Set the new revision as active
+  };
+
+  // Create a new array of tasks with the updated task
+  const updatedTasks = [...taskPlan.tasks];
+  updatedTasks[taskIndex] = updatedTask;
+
+  // Return the updated task plan
+  return {
+    ...taskPlan,
+    tasks: updatedTasks,
+  };
+}
+
+/**
+ * Helper function to get the active task from a TaskPlan
+ *
+ * @param taskPlan The task plan
+ * @returns The currently active task
+ * @throws Error if there are no tasks
+ */
+export function getActiveTask(taskPlan: TaskPlan): Task {
+  if (taskPlan.tasks.length === 0) {
+    throw new Error("No tasks available");
+  }
+
+  return taskPlan.tasks[taskPlan.activeTaskIndex];
+}
+
+/**
+ * Helper function to get the active plan items for the active task
+ *
+ * @param taskPlan The task plan
+ * @returns The currently active plan items
+ * @throws Error if there are no tasks or no plan revisions
+ */
+export function getActivePlanItems(taskPlan: TaskPlan): PlanItem[] {
+  const activeTask = getActiveTask(taskPlan);
+
+  if (activeTask.planRevisions.length === 0) {
+    throw new Error("No plan revisions available for the active task");
+  }
+
+  return activeTask.planRevisions[activeTask.activeRevisionIndex].plans;
+}
+
+/**
+ * Marks a specific plan item as completed and adds a summary.
+ * This operation modifies the current active revision directly and does NOT create a new revision.
+ *
+ * @param taskPlan The current task plan
+ * @param taskId The ID of the task containing the plan item
+ * @param planItemIndex The `index` property of the plan item to mark as completed
+ * @param summary Optional summary of the completed plan item. If undefined, existing summary is preserved.
+ * @returns The updated TaskPlan
+ * @throws Error if the task or plan item is not found, or if no active revision exists.
+ */
+export function completePlanItem(
+  taskPlan: TaskPlan,
+  taskId: string,
+  planItemIndex: number,
+  summary?: string,
+): TaskPlan {
+  const taskIndexInPlan = taskPlan.tasks.findIndex(
+    (task) => task.id === taskId,
+  );
+
+  if (taskIndexInPlan === -1) {
+    throw new Error(`Task with ID ${taskId} not found in task plan`);
+  }
+
+  const originalTask = taskPlan.tasks[taskIndexInPlan];
+
+  const activeRevisionIndex = originalTask.activeRevisionIndex;
+
+  // Ensure there's a planRevisions array and the activeRevisionIndex is valid
+  if (
+    !originalTask.planRevisions ||
+    activeRevisionIndex < 0 ||
+    activeRevisionIndex >= originalTask.planRevisions.length
+  ) {
+    throw new Error(
+      `Invalid active revision index (${activeRevisionIndex}) for task ${taskId}`,
+    );
+  }
+
+  const originalActiveRevision =
+    originalTask.planRevisions[activeRevisionIndex];
+
+  // This check should be covered by the index check, but reinforces intent
+  if (!originalActiveRevision) {
+    // This case implies an issue with activeRevisionIndex or planRevisions structure
+    throw new Error(
+      `Active revision (index ${activeRevisionIndex}) not found for task ${taskId}`,
+    );
+  }
+
+  const planItemToUpdateActualIndexInPlansArray =
+    originalActiveRevision.plans.findIndex(
+      (item) => item.index === planItemIndex,
+    );
+
+  if (planItemToUpdateActualIndexInPlansArray === -1) {
+    throw new Error(
+      `Plan item with .index ${planItemIndex} not found in active revision (index ${activeRevisionIndex}) of task ${taskId}`,
+    );
+  }
+
+  // Create a new 'plans' array with the specific item updated
+  const updatedPlansForRevision = originalActiveRevision.plans.map((item) => {
+    if (item.index === planItemIndex) {
+      const newSummary = summary !== undefined ? summary : item.summary;
+      return { ...item, completed: true, summary: newSummary };
+    }
+    return item;
+  });
+
+  // Create a new 'PlanRevision' object for the active revision, with the updated 'plans'
+  const updatedActiveRevision: PlanRevision = {
+    ...originalActiveRevision,
+    plans: updatedPlansForRevision,
+  };
+
+  // Create a new 'planRevisions' array, replacing the active revision with the updated one
+  const updatedPlanRevisions = [...originalTask.planRevisions];
+  updatedPlanRevisions[activeRevisionIndex] = updatedActiveRevision;
+
+  // Create a new 'Task' object with the updated 'planRevisions'
+  const updatedTask: Task = {
+    ...originalTask,
+    planRevisions: updatedPlanRevisions,
+  };
+
+  // Create a new 'tasks' array for the TaskPlan, replacing the updated task
+  const updatedTasksArray = [...taskPlan.tasks];
+  updatedTasksArray[taskIndexInPlan] = updatedTask;
+
+  // Return the new TaskPlan object
+  return {
+    ...taskPlan,
+    tasks: updatedTasksArray,
+  };
+}
+
+/**
+ * Marks a task as completed
+ *
+ * @param taskPlan The current task plan
+ * @param taskId The ID of the task to mark as completed
+ * @param summary Optional summary of the completed task
+ * @returns The updated TaskPlan
+ */
+export function completeTask(
+  taskPlan: TaskPlan,
+  taskId: string,
+  summary?: string,
+): TaskPlan {
+  const taskIndex = taskPlan.tasks.findIndex((task) => task.id === taskId);
+
+  if (taskIndex === -1) {
+    throw new Error(`Task with ID ${taskId} not found`);
+  }
+
+  const task = taskPlan.tasks[taskIndex];
+
+  // Create an updated task marked as completed
+  const updatedTask: Task = {
+    ...task,
+    completed: true,
+    completedAt: Date.now(),
+    summary,
+  };
+
+  // Create a new array of tasks with the updated task
+  const updatedTasks = [...taskPlan.tasks];
+  updatedTasks[taskIndex] = updatedTask;
+
+  // Return the updated task plan
+  return {
+    ...taskPlan,
+    tasks: updatedTasks,
+  };
+}