fix: nested task list display and checkbox interaction (#5575)

- Fix nested task lists not showing proper indentation
- Use simple CSS cascade with [&_ul.contains-task-list]:ml-6
- Fix checkbox clicks toggling wrong tasks in nested lists
- Search from memo root container for global task indexing
- Remove complex selectors in favor of standard approach
- Match behavior of GitHub, Notion, and other platforms

Closes #5575

web/src/components/MemoContent/TaskListItem.tsx

@@ -3,7 +3,7 @@ import { Checkbox } from "@/components/ui/checkbox";
 import { useUpdateMemo } from "@/hooks/useMemoQueries";
 import { toggleTaskAtIndex } from "@/utils/markdown-manipulation";
 import { useMemoViewContext, useMemoViewDerived } from "../MemoView/MemoViewContext";
-import { TASK_LIST_CLASS, TASK_LIST_ITEM_CLASS } from "./constants";
+import { TASK_LIST_ITEM_CLASS } from "./constants";
 import type { ReactMarkdownProps } from "./markdown/types";
 
 interface TaskListItemProps extends React.InputHTMLAttributes<HTMLInputElement>, ReactMarkdownProps {
@@ -35,14 +35,12 @@ export const TaskListItem: React.FC<TaskListItemProps> = ({ checked, node: _node
     if (taskIndexStr !== null) {
       taskIndex = parseInt(taskIndexStr);
     } else {
-      // Fallback: Calculate index by counting task list items
-      // Walk up to find the parent element with all task items
-      let searchRoot = listItem.parentElement;
-      while (searchRoot && !searchRoot.classList.contains(TASK_LIST_CLASS)) {
-        searchRoot = searchRoot.parentElement;
-      }
+      // Fallback: Calculate index by counting all task list items in the entire memo
+      // We need to search from the root memo content container, not just the nearest list
+      // to ensure nested tasks are counted in document order
+      let searchRoot = listItem.closest('[class*="memo-content"], [class*="MemoContent"]');
 
-      // If not found, search from the document root
+      // If memo content container not found, search from document body
       if (!searchRoot) {
         searchRoot = document.body;
       }

web/src/components/MemoContent/markdown/List.tsx

@@ -19,7 +19,11 @@ export const List = ({ ordered, children, className, node: _node, ...domProps }:
     <Component
       className={cn(
         "my-0 mb-2 list-outside",
-        isTaskList ? "pl-0 list-none" : cn("pl-6", ordered ? "list-decimal" : "list-disc"),
+        isTaskList
+          ? // Task list: no bullets, nested lists get left margin for indentation
+            "list-none [&_ul.contains-task-list]:ml-6"
+          : // Regular list: standard padding and list style
+            cn("pl-6", ordered ? "list-decimal" : "list-disc"),
         className,
       )}
       {...domProps}
@@ -46,10 +50,10 @@ export const ListItem = ({ children, className, node: _node, ...domProps }: List
       <li
         className={cn(
           "mt-0.5 leading-6 list-none",
-          // Task item styles: checkbox margins, inline paragraph, nested list indent
+          // Checkbox styling: margin and alignment
           "[&>button]:mr-2 [&>button]:align-middle",
+          // Inline paragraph for task text
           "[&>p]:inline [&>p]:m-0",
-          `[&>.${TASK_LIST_CLASS}]:pl-6`,
           className,
         )}
         {...domProps}