feat(surfaces): todo task list sidebar view

Add a dedicated "Tasks" sidebar view for the per-conversation todo surface
(model-maintained via todo_write tool; read-only, conversation-scoped).

- parseTodoPayload: pure parser for the rendererId: "todo" custom field
  (TodoItem { content, status, priority } — types defined FE-side, not in wire)
- TodoList.svelte: renders the task list with status indicators (spinner for
  in_progress, checkmark for completed, X for cancelled, empty circle for
  pending) + priority dots (red/yellow/gray)
- SurfaceView dispatches rendererId: "todo" to TodoList
- App.svelte: "Tasks" view kind (always visible; "No tasks yet" empty state),
  todo surface pulled out of the generic Extensions list, re-mounts per
  conversation via {#key}

681 tests green.

2 files changed, 73 insertions, 0 deletions

diff --git a/src/features/surface-host/ui/SurfaceView.svelte b/src/features/surface-host/ui/SurfaceView.svelte
index e5f807a..3f92e3b 100644
--- a/src/features/surface-host/ui/SurfaceView.svelte
+++ b/src/features/surface-host/ui/SurfaceView.svelte
@@ -8,6 +8,7 @@
 	import Selector from "./Selector.svelte";
 	import StatTable from "./StatTable.svelte";
 	import SurfaceTable from "./SurfaceTable.svelte";
+	import TodoList from "./TodoList.svelte";
 	import Toggle from "./Toggle.svelte";
 
 	let {
@@ -43,6 +44,8 @@
 				<SurfaceTable payload={group.field.payload} />
 			{:else if group.field.rendererId === "message-queue"}
 				<MessageQueueList payload={group.field.payload} />
+			{:else if group.field.rendererId === "todo"}
+				<TodoList payload={group.field.payload} />
 			{/if}
 		{/if}
 	{/each}
diff --git a/src/features/surface-host/ui/TodoList.svelte b/src/features/surface-host/ui/TodoList.svelte
new file mode 100644
index 0000000..8dbd995
--- /dev/null
+++ b/src/features/surface-host/ui/TodoList.svelte
@@ -0,0 +1,70 @@
+<script lang="ts">
+	import { parseTodoPayload, type TodoPriority, type TodoStatus } from "../logic/todo";
+
+	let { payload }: { readonly payload: unknown } = $props();
+
+	const data = $derived(parseTodoPayload(payload));
+
+	const priorityDot: Record<TodoPriority, string> = {
+		high: "bg-error",
+		medium: "bg-warning",
+		low: "bg-base-content/30",
+	};
+</script>
+
+{#if data !== null && data.todos.length > 0}
+	<ul class="flex flex-col gap-1">
+		{#each data.todos as todo, i (i)}
+			<li class="flex items-start gap-2 rounded-box bg-base-200 px-3 py-2 text-sm">
+				<!-- Status indicator -->
+				<span class="mt-0.5 shrink-0">
+					{#if todo.status === "in_progress"}
+						<span class="loading loading-spinner loading-xs text-primary"></span>
+					{:else if todo.status === "completed"}
+						<svg
+							xmlns="http://www.w3.org/2000/svg"
+							viewBox="0 0 24 24"
+							fill="none"
+							stroke="currentColor"
+							stroke-width="3"
+							stroke-linecap="round"
+							stroke-linejoin="round"
+							class="h-4 w-4 text-success"
+						>
+							<polyline points="20 6 9 17 4 12"></polyline>
+						</svg>
+					{:else if todo.status === "cancelled"}
+						<svg
+							xmlns="http://www.w3.org/2000/svg"
+							viewBox="0 0 24 24"
+							fill="none"
+							stroke="currentColor"
+							stroke-width="3"
+							stroke-linecap="round"
+							stroke-linejoin="round"
+							class="h-4 w-4 text-base-content/40"
+						>
+							<line x1="18" y1="6" x2="6" y2="18"></line>
+							<line x1="6" y1="6" x2="18" y2="18"></line>
+						</svg>
+					{:else}
+						<!-- pending: empty circle -->
+						<span class="block h-4 w-4 rounded-full border-2 border-base-content/30"></span>
+					{/if}
+				</span>
+
+				<!-- Content -->
+				<span
+					class:flex-1={true}
+					class:line-through={todo.status === "completed" || todo.status === "cancelled"}
+					class:opacity-50={todo.status === "completed" || todo.status === "cancelled"}
+				>
+					{todo.content}
+				</span>
+
+				<!-- Priority dot -->
+				<span class="mt-1 h-2 w-2 shrink-0 rounded-full {priorityDot[todo.priority]}"></span>
+			</li>
+		{/each}
+	</ul>
+{/if}