refactor(web): extract list auto-completion logic into custom hook

- Create useListAutoCompletion hook to encapsulate list continuation logic
- Simplify handleEditorKeyDown in Editor component
- Improve code organization and testability
- Add comprehensive documentation for the hook
- Maintain all existing functionality for markdown lists

The handleEditorKeyDown function is now much cleaner, delegating
list auto-completion concerns to a dedicated, reusable hook.

web/src/components/MemoEditor/Editor/index.tsx

@@ -1,10 +1,10 @@
 import { forwardRef, ReactNode, useCallback, useEffect, useImperativeHandle, useRef, useState } from "react";
 import { cn } from "@/lib/utils";
-import { detectLastListItem, generateListContinuation } from "@/utils/markdown-list-detection";
 import { Command } from "../types/command";
 import CommandSuggestions from "./CommandSuggestions";
 import TagSuggestions from "./TagSuggestions";
 import { editorCommands } from "./commands";
+import { useListAutoCompletion } from "./useListAutoCompletion";
 
 export interface EditorRefActions {
   getEditor: () => HTMLTextAreaElement | null;
@@ -152,22 +152,14 @@ const Editor = forwardRef(function Editor(props: Props, ref: React.ForwardedRef<
     updateEditorHeight();
   }, []);
 
-  const handleEditorKeyDown = async (event: React.KeyboardEvent<HTMLTextAreaElement>) => {
-    if (event.key === "Enter" && !isInIME) {
-      if (event.shiftKey || event.ctrlKey || event.metaKey || event.altKey) {
-        return;
-      }
+  const { handleEnterKey } = useListAutoCompletion({
+    editorActions,
+    isInIME,
+  });
 
-      const cursorPosition = editorActions.getCursorPosition();
-      const prevContent = editorActions.getContent().substring(0, cursorPosition);
-
-      // Detect list item using regex-based detection
-      const listInfo = detectLastListItem(prevContent);
-      if (listInfo.type) {
-        event.preventDefault();
-        const insertText = "\n" + generateListContinuation(listInfo);
-        editorActions.insertText(insertText);
-      }
+  const handleEditorKeyDown = (event: React.KeyboardEvent<HTMLTextAreaElement>) => {
+    if (event.key === "Enter") {
+      handleEnterKey(event);
     }
   };
 

web/src/components/MemoEditor/Editor/useListAutoCompletion.ts

@@ -0,0 +1,57 @@
+import { useCallback } from "react";
+import { detectLastListItem, generateListContinuation } from "@/utils/markdown-list-detection";
+import { EditorRefActions } from ".";
+
+interface UseListAutoCompletionOptions {
+  editorActions: EditorRefActions;
+  isInIME: boolean;
+}
+
+/**
+ * Custom hook for handling markdown list auto-completion.
+ * When the user presses Enter on a list item, this hook automatically
+ * continues the list with the appropriate formatting.
+ *
+ * Supports:
+ * - Ordered lists (1. item, 2. item, etc.)
+ * - Unordered lists (- item, * item, + item)
+ * - Task lists (- [ ] task, - [x] task)
+ * - Nested lists with proper indentation
+ */
+export function useListAutoCompletion({ editorActions, isInIME }: UseListAutoCompletionOptions) {
+  /**
+   * Handles the Enter key press to auto-complete list items.
+   * Returns true if the event was handled, false otherwise.
+   */
+  const handleEnterKey = useCallback(
+    (event: React.KeyboardEvent<HTMLTextAreaElement>): boolean => {
+      // Don't handle if in IME composition (for Asian languages)
+      if (isInIME) {
+        return false;
+      }
+
+      // Don't handle if modifier keys are pressed (user wants manual control)
+      if (event.shiftKey || event.ctrlKey || event.metaKey || event.altKey) {
+        return false;
+      }
+
+      const cursorPosition = editorActions.getCursorPosition();
+      const contentBeforeCursor = editorActions.getContent().substring(0, cursorPosition);
+
+      // Detect if we're on a list item
+      const listInfo = detectLastListItem(contentBeforeCursor);
+
+      if (listInfo.type) {
+        event.preventDefault();
+        const continuation = generateListContinuation(listInfo);
+        editorActions.insertText("\n" + continuation);
+        return true;
+      }
+
+      return false;
+    },
+    [editorActions, isInIME],
+  );
+
+  return { handleEnterKey };
+}