feat: add task list button to rich text editor toolbar

Register TaskList and TaskItem TipTap extensions, add "Task list" option
to the List dropdown in the formatting toolbar, and consolidate task list
CSS between the editor and markdown-it preview into shared styles in
app.css.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.css

@@ -102,3 +102,77 @@ body::before {
 .tiptap .selectedCell {
 	background-color: color-mix(in srgb, var(--primary) 12%, transparent);
 }
+
+/* Task list styles — shared between TipTap editor and markdown-it preview */
+
+/* TipTap: ul[data-type="taskList"]  |  markdown-it: ul.task-list */
+.tiptap ul[data-type="taskList"],
+.prose ul.task-list {
+	list-style: none;
+	padding-left: 0;
+	margin: 0.25rem 0;
+}
+
+.tiptap ul[data-type="taskList"] li,
+.prose ul.task-list li {
+	display: flex;
+	align-items: center;
+	gap: 0.375rem;
+	margin: 0;
+	padding: 0;
+}
+
+.tiptap ul[data-type="taskList"] li::marker,
+.prose ul.task-list li::marker {
+	content: none;
+}
+
+/* TipTap: checkbox is inside a label */
+.tiptap ul[data-type="taskList"] li label {
+	display: flex;
+	align-items: center;
+	flex-shrink: 0;
+}
+
+/* Shared checkbox styles */
+.tiptap ul[data-type="taskList"] li label input[type="checkbox"],
+.prose ul.task-list .task-checkbox {
+	cursor: pointer;
+	margin: 0;
+	flex-shrink: 0;
+}
+
+/* TipTap: text content is in a div>p */
+.tiptap ul[data-type="taskList"] li > div {
+	flex: 1;
+	min-width: 0;
+}
+
+.tiptap ul[data-type="taskList"] li > div p {
+	margin: 0;
+}
+
+/* Checked item styling */
+.tiptap ul[data-type="taskList"] li[data-checked="true"] > div {
+	text-decoration: line-through;
+	color: var(--text-muted);
+}
+
+/* Override prose spacing for task lists */
+.prose ul[data-type="taskList"],
+.prose ul.task-list {
+	padding-left: 0;
+	margin-top: 0.25rem;
+	margin-bottom: 0.25rem;
+}
+
+.prose ul[data-type="taskList"] li,
+.prose ul.task-list li {
+	padding-left: 0;
+	margin-top: 0;
+	margin-bottom: 0;
+}
+
+.prose ul.task-list li p {
+	margin: 0;
+}

src/lib/components/FormattingToolbar.svelte

@@ -6,6 +6,7 @@
 		Heading,
 		List,
 		ListOrdered,
+		ListChecks,
 		TextQuote,
 		CodeXml,
 		Bold,
@@ -222,7 +223,7 @@
 	<div class="relative" data-dropdown="list">
 		<button
 			onclick={() => toggleDropdown('list')}
-			class={dropdownBtnClass(isActive('bulletList') || isActive('orderedList'))}
+			class={dropdownBtnClass(isActive('bulletList') || isActive('orderedList') || isActive('taskList'))}
 			title="Lists"
 			data-testid="format-list"
 		>
@@ -247,6 +248,14 @@
 					<ListOrdered size={iconSize} />
 					<span>Ordered list</span>
 				</button>
+				<button
+					onclick={() => { editor?.chain().focus().toggleTaskList().run(); closeDropdowns(); }}
+					class={dropdownItemClass(isActive('taskList'))}
+					data-testid="format-task-list"
+				>
+					<ListChecks size={iconSize} />
+					<span>Task list</span>
+				</button>
 			</div>
 		{/if}
 	</div>

src/lib/components/NoteCard.svelte

@@ -237,24 +237,3 @@
 	{/if}
 </article>
 
-<style>
-	article :global(.prose li:has(.task-checkbox)) {
-		list-style: none;
-		display: flex;
-		align-items: flex-start;
-		gap: 0.25rem;
-	}
-
-	article :global(.prose li:has(.task-checkbox))::before {
-		display: none;
-	}
-
-	article :global(.prose li:has(.task-checkbox))::marker {
-		content: none;
-	}
-
-	article :global(.task-checkbox) {
-		margin-top: 0.15rem;
-		flex-shrink: 0;
-	}
-</style>

src/lib/components/TiptapEditor.svelte

@@ -10,6 +10,8 @@
 	import { TableRow } from '@tiptap/extension-table-row';
 	import { TableHeader } from '@tiptap/extension-table-header';
 	import { TableCell } from '@tiptap/extension-table-cell';
+	import TaskList from '@tiptap/extension-task-list';
+	import TaskItem from '@tiptap/extension-task-item';
 	import { Markdown } from 'tiptap-markdown';
 
 	interface Props {
@@ -38,6 +40,8 @@
 				TableRow,
 				TableHeader,
 				TableCell,
+					TaskList,
+				TaskItem.configure({ nested: true }),
 				Markdown
 			],
 			content,

src/lib/utils/markdown.ts

@@ -24,6 +24,17 @@ md.core.ruler.after('inline', 'task-lists', (state) => {
 			const token = new state.Token('html_inline', '', 0);
 			token.content = checkbox;
 			tokens[i].children!.unshift(token);
+
+			// Add task-list class to parent <ul> (once)
+			for (let j = i - 1; j >= 0; j--) {
+				if (tokens[j].type === 'bullet_list_open') {
+					const cls = tokens[j].attrGet('class') ?? '';
+					if (!cls.includes('task-list')) {
+						tokens[j].attrJoin('class', 'task-list');
+					}
+					break;
+				}
+			}
 		}
 	}
 });