Feature: Add rich interactive Markdown renderer, wide adaptive memo panel, and custom language popover

next-env.d.ts

@@ -1,7 +1,7 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
+import "./.next/types/routes.d.ts";
-import "./.next/dev/types/root-params.d.ts";
+import "./.next/types/root-params.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

package.json

@@ -16,11 +16,13 @@
     "@prisma/client": "^6.19.3",
     "bcryptjs": "^3.0.3",
     "csv-parse": "^7.0.2",
+    "marked": "^18.0.10",
     "next": "16.3.1",
     "next-auth": "^4.24.15",
     "prisma": "^6.19.3",
     "react": "19.2.8",
     "react-dom": "19.2.8",
+    "react-markdown": "^10.1.0",
     "uuid": "^14.0.2"
   },
   "devDependencies": {

src/app/globals.css

@@ -63,7 +63,7 @@
 
   /* Layout */
   --sidebar-width: 240px;
-  --detail-width: 360px;
+  --detail-width: min(560px, 48vw);
   --header-height: 56px;
 }
 
@@ -701,38 +701,56 @@ a { color: inherit; text-decoration: none; }
 
 /* Note area - the wide memo */
 .note-editor-wrap {
-  background: var(--bg-secondary);
+  background: var(--bg-primary);
   border: 1px solid var(--border);
   border-radius: var(--radius-md);
   overflow: hidden;
-  min-height: 200px;
   display: flex;
   flex-direction: column;
+  flex: 1;
+  min-height: 280px;
+  box-shadow: var(--shadow-xs);
   transition: border-color var(--dur-fast), box-shadow var(--dur-fast);
 }
 
 .note-editor-wrap:focus-within {
   border-color: var(--accent);
-  box-shadow: 0 0 0 3px var(--accent-light);
+  box-shadow: 0 0 0 2px var(--accent-light);
 }
 
 .note-editor-toolbar {
   display: flex;
-  gap: 2px;
+  align-items: center;
-  padding: 6px 8px;
+  gap: 3px;
+  padding: 6px 10px;
   border-bottom: 1px solid var(--border);
-  background: var(--bg-primary);
+  background: var(--bg-secondary);
+  flex-wrap: wrap;
+}
+
+.note-toolbar-group {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+}
+
+.note-toolbar-divider {
+  width: 1px;
+  height: 18px;
+  background: var(--border-medium);
+  margin: 0 4px;
 }
 
 .note-toolbar-btn {
-  width: 26px;
   height: 26px;
+  min-width: 26px;
+  padding: 0 5px;
   border-radius: var(--radius-xs);
   display: flex;
   align-items: center;
   justify-content: center;
   font-size: 12px;
-  font-weight: 700;
+  font-weight: 600;
   color: var(--text-secondary);
   cursor: pointer;
   transition: background var(--dur-fast), color var(--dur-fast);
@@ -743,6 +761,255 @@ a { color: inherit; text-decoration: none; }
   color: var(--text-primary);
 }
 
+.note-toolbar-btn.active {
+  background: var(--accent-light);
+  color: var(--accent);
+}
+
+.note-textarea {
+  flex: 1;
+  width: 100%;
+  background: transparent;
+  color: var(--text-primary);
+  font-size: 14px;
+  line-height: 1.7;
+  padding: 16px;
+  resize: none;
+  min-height: 240px;
+  font-family: inherit;
+}
+
+.note-textarea::placeholder { color: var(--text-tertiary); }
+
+/* ============================================
+   MARKDOWN PREVIEW STYLES
+   ============================================ */
+.markdown-body {
+  flex: 1;
+  padding: 16px;
+  color: var(--text-primary);
+  font-size: 14px;
+  line-height: 1.7;
+  overflow-y: auto;
+  min-height: 240px;
+  background: var(--bg-primary);
+}
+
+.markdown-body h1,
+.markdown-body h2,
+.markdown-body h3,
+.markdown-body h4 {
+  font-weight: 700;
+  color: var(--text-primary);
+  margin-top: 18px;
+  margin-bottom: 8px;
+  line-height: 1.35;
+  letter-spacing: -0.3px;
+}
+
+.markdown-body h1:first-child,
+.markdown-body h2:first-child,
+.markdown-body h3:first-child {
+  margin-top: 0;
+}
+
+.markdown-body h1 { font-size: 20px; border-bottom: 1px solid var(--border); padding-bottom: 6px; }
+.markdown-body h2 { font-size: 17px; }
+.markdown-body h3 { font-size: 15px; }
+
+.markdown-body p {
+  margin-bottom: 12px;
+}
+
+.markdown-body p:last-child {
+  margin-bottom: 0;
+}
+
+.markdown-body strong {
+  font-weight: 700;
+  color: var(--text-primary);
+}
+
+.markdown-body em {
+  font-style: italic;
+}
+
+.markdown-body del {
+  text-decoration: line-through;
+  opacity: 0.6;
+}
+
+.markdown-body ul,
+.markdown-body ol {
+  margin-bottom: 12px;
+  padding-left: 22px;
+}
+
+.markdown-body li {
+  margin-bottom: 4px;
+}
+
+.markdown-body blockquote {
+  border-left: 3px solid var(--accent);
+  padding: 6px 12px;
+  margin: 12px 0;
+  background: var(--accent-light);
+  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
+  color: var(--text-secondary);
+  font-size: 13.5px;
+}
+
+.markdown-body code {
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
+  font-size: 12.5px;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border);
+  padding: 2px 5px;
+  border-radius: var(--radius-xs);
+  color: var(--accent);
+}
+
+.markdown-body pre {
+  background: var(--bg-secondary);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  padding: 12px;
+  margin: 12px 0;
+  overflow-x: auto;
+}
+
+.markdown-body pre code {
+  background: none;
+  border: none;
+  padding: 0;
+  color: var(--text-primary);
+  font-size: 13px;
+}
+
+.markdown-body a {
+  color: var(--accent);
+  text-decoration: underline;
+  text-underline-offset: 2px;
+}
+
+.markdown-body hr {
+  border: none;
+  border-top: 1px solid var(--border);
+  margin: 16px 0;
+}
+
+.markdown-body img {
+  max-width: 100%;
+  border-radius: var(--radius-sm);
+  margin: 8px 0;
+}
+
+/* Interactive Checkbox in Markdown */
+.markdown-checkbox-item {
+  display: flex;
+  align-items: flex-start;
+  gap: 8px;
+  margin: 6px 0;
+  cursor: pointer;
+  user-select: none;
+}
+
+.markdown-checkbox-box {
+  width: 16px;
+  height: 16px;
+  border-radius: 4px;
+  border: 1.5px solid var(--border-strong);
+  margin-top: 3px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  transition: all var(--dur-fast);
+}
+
+.markdown-checkbox-box.checked {
+  background: var(--accent);
+  border-color: var(--accent);
+}
+
+.markdown-checkbox-box.checked::after {
+  content: "";
+  width: 4px;
+  height: 8px;
+  border: 1.5px solid white;
+  border-top: none;
+  border-left: none;
+  transform: rotate(45deg) translateY(-1px);
+}
+
+/* Custom Language Selector Popover */
+.lang-selector-wrap {
+  position: relative;
+}
+
+.lang-btn {
+  display: flex;
+  align-items: center;
+  gap: 5px;
+  padding: 4px 8px;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  color: var(--text-secondary);
+  font-size: 12px;
+  font-weight: 600;
+  cursor: pointer;
+  transition: all var(--dur-fast);
+}
+
+.lang-btn:hover {
+  background: var(--bg-hover);
+  color: var(--text-primary);
+  border-color: var(--border-medium);
+}
+
+.lang-dropdown {
+  position: absolute;
+  top: calc(100% + 4px);
+  right: 0;
+  background: var(--bg-primary);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  box-shadow: var(--shadow-md);
+  padding: 4px;
+  min-width: 120px;
+  z-index: 60;
+  animation: dropdownIn var(--dur-fast) var(--ease-out);
+}
+
+.lang-option {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 6px 10px;
+  font-size: 12.5px;
+  font-weight: 500;
+  color: var(--text-primary);
+  border-radius: var(--radius-xs);
+  cursor: pointer;
+  transition: background var(--dur-fast);
+}
+
+.lang-option:hover {
+  background: var(--bg-hover);
+}
+
+.lang-option.selected {
+  color: var(--accent);
+  font-weight: 700;
+  background: var(--accent-light);
+}
+
+.note-toolbar-btn:hover {
+  background: var(--bg-hover);
+  color: var(--text-primary);
+}
+
 .note-textarea {
   flex: 1;
   width: 100%;

src/app/login/page.tsx

@@ -1,10 +1,11 @@
-"use client";
+"use client";
 import { useState } from "react";
 import { signIn } from "next-auth/react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { useI18n, Language } from "@/lib/i18n";
+import { useI18n } from "@/lib/i18n";
 import { useTheme } from "@/app/providers";
+import { LanguageSelector } from "@/components/ui/LanguageSelector";
 
 export default function LoginPage() {
   const router = useRouter();
@@ -44,25 +45,7 @@ export default function LoginPage() {
             <span className="auth-logo-name">{t("appName")}</span>
           </div>
           <div style={{ display: "flex", alignItems: "center", gap: 6 }}>
-            <select
+            <LanguageSelector />
-              aria-label={t("language")}
-              value={lang}
-              onChange={(e) => setLang(e.target.value as Language)}
-              style={{
-                background: "var(--bg-secondary)",
-                color: "var(--text-secondary)",
-                border: "1px solid var(--border)",
-                borderRadius: "var(--radius-xs)",
-                fontSize: 11,
-                padding: "3px 6px",
-                cursor: "pointer",
-                fontWeight: 600,
-              }}
-            >
-              <option value="en">EN</option>
-              <option value="ko">한국어</option>
-              <option value="ja">日本語</option>
-            </select>
 
             <button
               className="icon-btn"

src/app/register/page.tsx

@@ -1,10 +1,11 @@
-"use client";
+"use client";
 import { useState } from "react";
 import { signIn } from "next-auth/react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { useI18n, Language } from "@/lib/i18n";
+import { useI18n } from "@/lib/i18n";
 import { useTheme } from "@/app/providers";
+import { LanguageSelector } from "@/components/ui/LanguageSelector";
 
 export default function RegisterPage() {
   const router = useRouter();
@@ -60,25 +61,7 @@ export default function RegisterPage() {
             <span className="auth-logo-name">{t("appName")}</span>
           </div>
           <div style={{ display: "flex", alignItems: "center", gap: 6 }}>
-            <select
+            <LanguageSelector />
-              aria-label={t("language")}
-              value={lang}
-              onChange={(e) => setLang(e.target.value as Language)}
-              style={{
-                background: "var(--bg-secondary)",
-                color: "var(--text-secondary)",
-                border: "1px solid var(--border)",
-                borderRadius: "var(--radius-xs)",
-                fontSize: 11,
-                padding: "3px 6px",
-                cursor: "pointer",
-                fontWeight: 600,
-              }}
-            >
-              <option value="en">EN</option>
-              <option value="ko">한국어</option>
-              <option value="ja">日本語</option>
-            </select>
 
             <button
               className="icon-btn"

src/components/layout/Sidebar.tsx

@@ -1,8 +1,9 @@
-"use client";
+"use client";
 import { useState, useEffect, useRef } from "react";
 import { signOut } from "next-auth/react";
 import { useI18n, Language } from "@/lib/i18n";
 import { useTheme, ThemeMode } from "@/app/providers";
+import { LanguageSelector } from "@/components/ui/LanguageSelector";
 
 interface User { id: string; name?: string | null; email?: string | null }
 interface List { id: string; name: string; color: string; icon: string; _count?: { tasks: number } }
@@ -170,27 +171,9 @@ export function Sidebar({
         </div>
 
         {/* Top Quick Actions (Lang & Theme) */}
-        <div style={{ marginLeft: "auto", display: "flex", alignItems: "center", gap: 4 }}>
+        <div style={{ marginLeft: "auto", display: "flex", alignItems: "center", gap: 6 }}>
-          {/* Language Selector */}
+          {/* Custom Language Selector Popover */}
-          <select
+          <LanguageSelector />
-            aria-label={t("language")}
-            value={lang}
-            onChange={(e) => setLang(e.target.value as Language)}
-            style={{
-              background: "var(--bg-secondary)",
-              color: "var(--text-secondary)",
-              border: "1px solid var(--border)",
-              borderRadius: "var(--radius-xs)",
-              fontSize: 11,
-              padding: "3px 4px",
-              cursor: "pointer",
-              fontWeight: 600,
-            }}
-          >
-            <option value="en">EN</option>
-            <option value="ko">한국어</option>
-            <option value="ja">日本語</option>
-          </select>
 
           {/* Theme 3-Way Toggle Button */}
           <button

src/components/tasks/MarkdownNoteEditor.tsx

@@ -0,0 +1,325 @@
+"use client";
+import React, { useState, useRef, useCallback } from "react";
+import { marked } from "marked";
+import { useI18n } from "@/lib/i18n";
+
+interface MarkdownNoteEditorProps {
+  value: string;
+  onChange: (newValue: string) => void;
+  onSave?: () => void;
+}
+
+export function MarkdownNoteEditor({ value, onChange, onSave }: MarkdownNoteEditorProps) {
+  const { t } = useI18n();
+  const [mode, setMode] = useState<"edit" | "preview">("preview");
+  const textareaRef = useRef<HTMLTextAreaElement>(null);
+
+  // Insert markdown syntax at selection or cursor position
+  const insertSyntax = useCallback(
+    (before: string, after = "", placeholder = "") => {
+      const ta = textareaRef.current;
+      if (!ta) {
+        onChange(value + before + placeholder + after);
+        return;
+      }
+      const start = ta.selectionStart ?? ta.value.length;
+      const end = ta.selectionEnd ?? ta.value.length;
+      const selected = ta.value.slice(start, end) || placeholder;
+      const newVal = ta.value.slice(0, start) + before + selected + after + ta.value.slice(end);
+      onChange(newVal);
+
+      requestAnimationFrame(() => {
+        ta.focus();
+        ta.selectionStart = start + before.length;
+        ta.selectionEnd = start + before.length + selected.length;
+      });
+    },
+    [onChange, value]
+  );
+
+  // Keyboard shortcuts
+  const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
+    if ((e.ctrlKey || e.metaKey) && e.key === "b") {
+      e.preventDefault();
+      insertSyntax("**", "**", "bold");
+    } else if ((e.ctrlKey || e.metaKey) && e.key === "i") {
+      e.preventDefault();
+      insertSyntax("*", "*", "italic");
+    } else if ((e.ctrlKey || e.metaKey) && e.key === "s") {
+      e.preventDefault();
+      if (onSave) onSave();
+    } else if (e.key === "Tab") {
+      e.preventDefault();
+      insertSyntax("  ");
+    }
+  };
+
+  // Toggle interactive checkboxes in markdown preview
+  const handlePreviewCheckboxToggle = (index: number) => {
+    const lines = value.split("\n");
+    let checkboxCount = 0;
+    const newLines = lines.map((line) => {
+      const match = line.match(/^(\s*[-*+]\s*\[)([ xX])(\])(.*)$/);
+      if (match) {
+        if (checkboxCount === index) {
+          const currentChecked = match[2].toLowerCase() === "x";
+          const newChecked = currentChecked ? " " : "x";
+          checkboxCount++;
+          return `${match[1]}${newChecked}${match[3]}${match[4]}`;
+        }
+        checkboxCount++;
+      }
+      return line;
+    });
+    onChange(newLines.join("\n"));
+  };
+
+  // Convert markdown to sanitized HTML with interactive checkboxes
+  const renderMarkdownHtml = () => {
+    if (!value || !value.trim()) {
+      return `<p style="color: var(--text-tertiary); font-style: italic;">${t("notesPlaceholder").split("\n")[0]}</p>`;
+    }
+
+    try {
+      let rawHtml = marked.parse(value, { breaks: true, gfm: true }) as string;
+
+      // Replace task list checkboxes with interactive ones
+      let cbIdx = 0;
+      rawHtml = rawHtml.replace(/<input[^>]*type="checkbox"[^>]*checked[^>]*>/gi, () => {
+        const id = `cb-${cbIdx++}`;
+        return `<span class="markdown-checkbox-box checked" data-idx="${id}"></span>`;
+      });
+      rawHtml = rawHtml.replace(/<input[^>]*type="checkbox"[^>]*>/gi, () => {
+        const id = `cb-${cbIdx++}`;
+        return `<span class="markdown-checkbox-box" data-idx="${id}"></span>`;
+      });
+
+      return rawHtml;
+    } catch {
+      return value;
+    }
+  };
+
+  return (
+    <div className="note-editor-wrap">
+      {/* Top Toolbar */}
+      <div className="note-editor-toolbar">
+        {/* Mode Switcher Tabs */}
+        <div className="note-toolbar-group">
+          <button
+            type="button"
+            className={`note-toolbar-btn${mode === "preview" ? " active" : ""}`}
+            onClick={() => setMode("preview")}
+            title="Preview rendered Markdown"
+          >
+            👁️ Preview
+          </button>
+          <button
+            type="button"
+            className={`note-toolbar-btn${mode === "edit" ? " active" : ""}`}
+            onClick={() => {
+              setMode("edit");
+              setTimeout(() => textareaRef.current?.focus(), 50);
+            }}
+            title="Edit raw Markdown"
+          >
+            ✏️ Edit
+          </button>
+        </div>
+
+        <div className="note-toolbar-divider" />
+
+        {/* Formatting actions */}
+        <div className="note-toolbar-group">
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="H1 Heading"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("# ", "", "Heading 1");
+            }}
+          >
+            H1
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="H2 Heading"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("## ", "", "Heading 2");
+            }}
+          >
+            H2
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="H3 Heading"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("### ", "", "Heading 3");
+            }}
+          >
+            H3
+          </button>
+        </div>
+
+        <div className="note-toolbar-divider" />
+
+        <div className="note-toolbar-group">
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Bold (Ctrl+B)"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("**", "**", "bold");
+            }}
+          >
+            <strong>B</strong>
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Italic (Ctrl+I)"
+            style={{ fontStyle: "italic" }}
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("*", "*", "italic");
+            }}
+          >
+            <em>I</em>
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Strikethrough"
+            style={{ textDecoration: "line-through" }}
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("~~", "~~", "strikethrough");
+            }}
+          >
+            S
+          </button>
+        </div>
+
+        <div className="note-toolbar-divider" />
+
+        <div className="note-toolbar-group">
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Checkbox item"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n- [ ] ", "", "task");
+            }}
+          >
+            ☑️
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Bullet list"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n- ", "", "list item");
+            }}
+          >
+            •
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Numbered list"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n1. ", "", "list item");
+            }}
+          >
+            1.
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Quote"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n> ", "", "quote");
+            }}
+          >
+            ❝
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Code Block"
+            style={{ fontFamily: "monospace" }}
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n```\n", "\n```\n", "code");
+            }}
+          >
+            {"< >"}
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Horizontal Divider"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("\n---\n");
+            }}
+          >
+            ―
+          </button>
+          <button
+            type="button"
+            className="note-toolbar-btn"
+            title="Link"
+            onClick={() => {
+              setMode("edit");
+              insertSyntax("[", "](https://example.com)", "link title");
+            }}
+          >
+            🔗
+          </button>
+        </div>
+      </div>
+
+      {/* Editor / Preview Content Area */}
+      {mode === "edit" ? (
+        <textarea
+          ref={textareaRef}
+          id="note-textarea"
+          className="note-textarea"
+          placeholder={t("notesPlaceholder")}
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+          onKeyDown={handleKeyDown}
+        />
+      ) : (
+        <div
+          className="markdown-body"
+          dangerouslySetInnerHTML={{ __html: renderMarkdownHtml() }}
+          onClick={(e) => {
+            const target = e.target as HTMLElement;
+            if (target.classList.contains("markdown-checkbox-box")) {
+              const idxStr = target.getAttribute("data-idx");
+              if (idxStr) {
+                const idx = parseInt(idxStr.replace("cb-", ""), 10);
+                if (!isNaN(idx)) handlePreviewCheckboxToggle(idx);
+              }
+            } else if (e.detail === 2) {
+              // Double click anywhere to quickly switch to edit mode
+              setMode("edit");
+            }
+          }}
+        />
+      )}
+    </div>
+  );
+}

src/components/tasks/TaskDetail.tsx

@@ -2,6 +2,7 @@
 import React, { useState, useEffect, useCallback, useRef } from "react";
 import { useI18n } from "@/lib/i18n";
 import { Task } from "./TaskList";
+import { MarkdownNoteEditor } from "./MarkdownNoteEditor";
 
 interface Props {
   task: Task;
@@ -32,11 +33,11 @@ export function TaskDetail({
   const [priority, setPriority] = useState(task.priority);
   const [newSubtitle, setNewSubtitle] = useState("");
   const [subtasks, setSubtasks] = useState(task.children || []);
+  const [showSubtasks, setShowSubtasks] = useState(true);
   const [saving, setSaving] = useState(false);
 
   const saveTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
   const currentTaskId = useRef(task.id);
-  const noteRef = useRef<HTMLTextAreaElement>(null);
 
   const priorityMap = [
     { label: t("priorityNone"), color: "var(--text-tertiary)", icon: "" },
@@ -113,32 +114,10 @@ export function TaskDetail({
     [save]
   );
 
-  // Insert markdown at cursor position
+  const handleNoteChange = (newNote: string) => {
-  const insertAtCursor = useCallback(
+    setNote(newNote);
-    (before: string, after = "", placeholder = "") => {
+    debounceSave({ note: newNote });
-      const ta = noteRef.current;
+  };
-      if (!ta) {
-        setNote((n) => {
-          const v = n + before + placeholder + after;
-          debounceSave({ note: v });
-          return v;
-        });
-        return;
-      }
-      const start = ta.selectionStart ?? ta.value.length;
-      const end = ta.selectionEnd ?? ta.value.length;
-      const selected = ta.value.slice(start, end) || placeholder;
-      const newVal = ta.value.slice(0, start) + before + selected + after + ta.value.slice(end);
-      setNote(newVal);
-      debounceSave({ note: newVal });
-      requestAnimationFrame(() => {
-        ta.focus();
-        ta.selectionStart = start + before.length;
-        ta.selectionEnd = start + before.length + selected.length;
-      });
-    },
-    [debounceSave]
-  );
 
   const handleToggleCompleted = useCallback(
     async (newCompleted: boolean) => {
@@ -306,7 +285,7 @@ export function TaskDetail({
 
   return (
     <aside className="detail-panel">
-      {/* Header */}
+      {/* Header Bar */}
       <div className="detail-header">
         <button
           className={`task-check-btn${task.completed ? " checked" : ""}`}
@@ -329,8 +308,8 @@ export function TaskDetail({
         </button>
       </div>
 
-      {/* Body */}
+      {/* Main Body - Centered on Wide Memo Experience */}
-      <div className="detail-body">
+      <div className="detail-body" style={{ display: "flex", flexDirection: "column", height: "100%", gap: 14 }}>
         {/* Title */}
         <textarea
           id="detail-title"
@@ -341,27 +320,32 @@ export function TaskDetail({
             debounceSave({ title: e.target.value });
           }}
           placeholder={t("taskTitlePlaceholder")}
-          rows={2}
+          rows={1}
           style={{
             textDecoration: task.completed ? "line-through" : "none",
             color: task.completed ? "var(--text-tertiary)" : "var(--text-primary)",
+            fontSize: 20,
+            fontWeight: 700,
           }}
         />
 
+        {/* Compact Metadata Strip (Priority & Due Date in a single line) */}
+        <div style={{ display: "flex", alignItems: "center", gap: 12, flexWrap: "wrap", paddingBottom: 4, borderBottom: "1px solid var(--border)" }}>
           {/* Priority */}
-        <div className="detail-section">
+          <div style={{ display: "flex", alignItems: "center", gap: 4 }}>
-          <div className="detail-section-label">{t("priority")}</div>
+            <span style={{ fontSize: 11, fontWeight: 600, color: "var(--text-tertiary)", textTransform: "uppercase" }}>{t("priority")}:</span>
-          <div className="priority-selector">
+            <div className="priority-selector" style={{ gap: 4 }}>
               {priorityMap.map((p, i) => (
                 <button
                   key={i}
                   id={`priority-${i}`}
                   className={`priority-btn${priority === i ? ` active-${["none", "low", "medium", "high"][i]}` : ""}`}
-                style={{ color: priority === i ? p.color : undefined }}
+                  style={{ color: priority === i ? p.color : undefined, padding: "3px 8px", fontSize: 11 }}
                   onClick={() => {
                     setPriority(i);
                     debounceSave({ priority: i });
                   }}
+                  type="button"
                 >
                   {p.icon && <span style={{ color: p.color }}>{p.icon}</span>}
                   {p.label}
@@ -370,10 +354,8 @@ export function TaskDetail({
             </div>
           </div>
 
-        {/* Due date */}
+          {/* Due Date */}
-        <div className="detail-section">
+          <div style={{ display: "flex", alignItems: "center", gap: 6, marginLeft: "auto" }}>
-          <div className="detail-section-label">{t("dueDate")}</div>
-          <div style={{ display: "flex", gap: 8, alignItems: "center" }}>
             <input
               id="due-date-input"
               type="date"
@@ -383,15 +365,17 @@ export function TaskDetail({
                 setDueDate(e.target.value);
                 debounceSave({ dueDate: e.target.value || null });
               }}
-              style={{ width: "auto" }}
+              style={{ width: "auto", padding: "3px 8px", fontSize: 12 }}
             />
             {dueDate && (
               <button
                 className="btn btn-ghost btn-sm"
+                style={{ padding: "2px 6px", fontSize: 11 }}
                 onClick={() => {
                   setDueDate("");
                   debounceSave({ dueDate: null });
                 }}
+                type="button"
               >
                 {t("clear")}
               </button>
@@ -399,51 +383,59 @@ export function TaskDetail({
           </div>
         </div>
 
-        {/* Notes — wide memo area */}
+        {/* The Wide Adaptive Markdown Note Editor (Takes ALL Remaining Space) */}
-        <div className="detail-section" style={{ flex: 1 }}>
+        <div style={{ flex: 1, display: "flex", flexDirection: "column", minHeight: 0 }}>
-          <div className="detail-section-label">{t("notes")}</div>
+          <MarkdownNoteEditor
-          <div className="note-editor-wrap">
-            <div className="note-editor-toolbar">
-              <button className="note-toolbar-btn" title={t("bold")} onClick={() => insertAtCursor("**", "**", "bold")}>B</button>
-              <button className="note-toolbar-btn" title={t("italic")} style={{ fontStyle: "italic" }} onClick={() => insertAtCursor("*", "*", "italic")}>I</button>
-              <button className="note-toolbar-btn" title={t("heading")} onClick={() => insertAtCursor("## ", "", "Heading")}>H</button>
-              <button className="note-toolbar-btn" title={t("bulletList")} onClick={() => insertAtCursor("\n- ", "", "item")}>•</button>
-              <button className="note-toolbar-btn" title={t("numberedList")} onClick={() => insertAtCursor("\n1. ", "", "item")}>1.</button>
-              <button className="note-toolbar-btn" title={t("checkbox")} onClick={() => insertAtCursor("\n- [ ] ", "", "task")}>☐</button>
-              <button className="note-toolbar-btn" title={t("code")} style={{ fontFamily: "monospace", fontSize: 11 }} onClick={() => insertAtCursor("`", "`", "code")}>{"`"}</button>
-            </div>
-            <textarea
-              ref={noteRef}
-              id="note-textarea"
-              className="note-textarea"
-              placeholder={t("notesPlaceholder")}
             value={note}
-              onChange={(e) => {
+            onChange={handleNoteChange}
-                setNote(e.target.value);
+            onSave={() => save(task.id, { note })}
-                debounceSave({ note: e.target.value });
-              }}
           />
         </div>
+
+        {/* Sub-tasks Section (Collapsible Accordion at Bottom) */}
+        <div style={{ borderTop: "1px solid var(--border)", paddingTop: 10 }}>
+          <div
+            style={{
+              display: "flex",
+              alignItems: "center",
+              justifyContent: "space-between",
+              cursor: "pointer",
+              userSelect: "none",
+              marginBottom: showSubtasks ? 8 : 0,
+            }}
+            onClick={() => setShowSubtasks((p) => !p)}
+          >
+            <div style={{ display: "flex", alignItems: "center", gap: 6 }}>
+              <svg
+                width="12"
+                height="12"
+                viewBox="0 0 24 24"
+                fill="none"
+                stroke="currentColor"
+                strokeWidth="2.5"
+                style={{ transform: showSubtasks ? "rotate(90deg)" : "rotate(0deg)", transition: "transform 0.15s" }}
+              >
+                <polyline points="9 18 15 12 9 6" />
+              </svg>
+              <span className="detail-section-label" style={{ marginBottom: 0 }}>{t("subtasks")}</span>
             </div>
 
-        {/* Sub-tasks */}
-        <div className="detail-section">
-          <div style={{ display: "flex", alignItems: "center", justifyContent: "space-between", marginBottom: 8 }}>
-            <div className="detail-section-label">{t("subtasks")}</div>
             {subtasks.length > 0 && (
-              <span style={{ fontSize: 11, color: "var(--text-tertiary)" }}>
+              <span style={{ fontSize: 11, color: "var(--text-tertiary)", fontWeight: 600 }}>
                 {completedCount}/{subtasks.length}
               </span>
             )}
           </div>
 
+          {showSubtasks && (
+            <div>
               {subtasks.length > 0 && (
-            <div className="progress-bar" style={{ marginBottom: 10 }}>
+                <div className="progress-bar" style={{ marginBottom: 8, height: 3 }}>
                   <div className="progress-bar-fill" style={{ width: `${progressPct}%` }} />
                 </div>
               )}
 
-          <div className="detail-subtasks">
+              <div className="detail-subtasks" style={{ maxHeight: 160, overflowY: "auto" }}>
                 {subtasks.map((sub) => (
                   <div
                     key={sub.id}
@@ -454,6 +446,7 @@ export function TaskDetail({
                       className={`subtask-check-btn${sub.completed ? " checked" : ""}`}
                       onClick={() => toggleSubtask(sub)}
                       aria-label="Toggle subtask"
+                      type="button"
                     />
                     <span className="detail-subtask-title">{sub.title}</span>
                     <button
@@ -461,6 +454,7 @@ export function TaskDetail({
                       style={{ width: 20, height: 20, opacity: 0.4 }}
                       onClick={() => deleteSubtask(sub.id)}
                       aria-label="Delete subtask"
+                      type="button"
                     >
                       <svg width="10" height="10" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
                         <line x1="18" y1="6" x2="6" y2="18" /><line x1="6" y1="6" x2="18" y2="18" />
@@ -468,12 +462,12 @@ export function TaskDetail({
                     </button>
                   </div>
                 ))}
-            <div className="add-subtask-row">
+                <div className="add-subtask-row" style={{ padding: "4px 8px" }}>
-              <span style={{ fontSize: 16, lineHeight: 1, color: "var(--accent)" }}>+</span>
+                  <span style={{ fontSize: 15, lineHeight: 1, color: "var(--accent)" }}>+</span>
                   <input
                     id="add-subtask-input"
                     placeholder={t("addSubtaskPlaceholder")}
-                style={{ flex: 1, background: "none", fontSize: 13, color: "var(--text-primary)" }}
+                    style={{ flex: 1, background: "none", fontSize: 12.5, color: "var(--text-primary)" }}
                     value={newSubtitle}
                     onChange={(e) => setNewSubtitle(e.target.value)}
                     onKeyDown={(e) => {
@@ -484,22 +478,26 @@ export function TaskDetail({
                     }}
                   />
                   {newSubtitle.trim() && (
-                <button className="btn btn-primary btn-sm" id="add-subtask-btn" onClick={addSubtask}>
+                    <button className="btn btn-primary btn-sm" id="add-subtask-btn" onClick={addSubtask} type="button">
                       {t("add")}
                     </button>
                   )}
                 </div>
               </div>
             </div>
+          )}
+        </div>
 
-        {/* Metadata */}
+        {/* Footer Timestamp */}
-        <div style={{ fontSize: 11, color: "var(--text-tertiary)", paddingTop: 8, borderTop: "1px solid var(--border)" }}>
+        <div style={{ fontSize: 11, color: "var(--text-tertiary)", display: "flex", justifyContent: "space-between" }}>
-          {t("created")}{" "}
+          <span>
+            {t("created")}:{" "}
             {new Date(task.createdAt).toLocaleDateString(lang === "ko" ? "ko-KR" : lang === "ja" ? "ja-JP" : "en-US", {
               year: "numeric",
               month: "short",
               day: "numeric",
             })}
+          </span>
         </div>
       </div>
     </aside>

src/components/ui/LanguageSelector.tsx

@@ -0,0 +1,77 @@
+"use client";
+import React, { useState, useRef, useEffect } from "react";
+import { useI18n, Language } from "@/lib/i18n";
+
+const LANGUAGES: { code: Language; label: string; flag: string }[] = [
+  { code: "en", label: "English", flag: "🇺🇸" },
+  { code: "ko", label: "한국어", flag: "🇰🇷" },
+  { code: "ja", label: "日本語", flag: "🇯🇵" },
+];
+
+export function LanguageSelector() {
+  const { lang, setLang } = useI18n();
+  const [open, setOpen] = useState(false);
+  const wrapRef = useRef<HTMLDivElement>(null);
+
+  const current = LANGUAGES.find((l) => l.code === lang) || LANGUAGES[0];
+
+  useEffect(() => {
+    const handleClickOutside = (e: MouseEvent) => {
+      if (wrapRef.current && !wrapRef.current.contains(e.target as Node)) {
+        setOpen(false);
+      }
+    };
+    if (open) document.addEventListener("mousedown", handleClickOutside);
+    return () => document.removeEventListener("mousedown", handleClickOutside);
+  }, [open]);
+
+  return (
+    <div className="lang-selector-wrap" ref={wrapRef}>
+      <button
+        className="lang-btn"
+        onClick={() => setOpen((p) => !p)}
+        aria-label="Select Language"
+        type="button"
+      >
+        <span style={{ fontSize: 13, lineHeight: 1 }}>🌐</span>
+        <span>{current.code.toUpperCase()}</span>
+        <svg
+          width="10"
+          height="10"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          strokeWidth="2.5"
+          style={{ transform: open ? "rotate(180deg)" : "rotate(0deg)", transition: "transform 0.15s" }}
+        >
+          <polyline points="6 9 12 15 18 9" />
+        </svg>
+      </button>
+
+      {open && (
+        <div className="lang-dropdown">
+          {LANGUAGES.map((item) => (
+            <div
+              key={item.code}
+              className={`lang-option${lang === item.code ? " selected" : ""}`}
+              onClick={() => {
+                setLang(item.code);
+                setOpen(false);
+              }}
+            >
+              <div style={{ display: "flex", alignItems: "center", gap: 6 }}>
+                <span>{item.flag}</span>
+                <span>{item.label}</span>
+              </div>
+              {lang === item.code && (
+                <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="3">
+                  <polyline points="20 6 9 17 4 12" />
+                </svg>
+              )}
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  );
+}