1 files changed, 49 insertions, 0 deletions
diff --git a/src/features/surface-host/logic/todo.ts b/src/features/surface-host/logic/todo.ts
new file mode 100644
index 0000000..8b8a5ef
--- /dev/null
+++ b/src/features/surface-host/logic/todo.ts
@@ -0,0 +1,49 @@
+/**
+ * Pure parser for the `rendererId: "todo"` custom-field payload.
+ *
+ * The `todo` backend extension maintains a per-conversation task list (written
+ * by the model via a `todo_write` tool) and exposes it as a read-only
+ * conversation-scoped surface with one `custom` field
+ * (`rendererId: "todo"`, `payload: TodoPayload`). This parser validates the
+ * untyped `payload: unknown` at the network seam so a hostile/partial payload
+ * can never crash the renderer (graceful skip → null).
+ *
+ * The `TodoItem` type is NOT in `@dispatch/wire` — it is defined by the `todo`
+ * extension and carried in the surface payload, so we define it here (the FE's
+ * rendering contract for the shape). Empty `todos` is a valid, parseable state
+ * (the model hasn't created a list / cleared it); the caller hides the panel.
+ */
+export type TodoStatus = "pending" | "in_progress" | "completed" | "cancelled";
+
+export interface TodoItem {
+  readonly content: string;
+  readonly status: TodoStatus;
+}
+
+export interface TodoData {
+  readonly todos: readonly TodoItem[];
+}
+
+const STATUSES = new Set<string>(["pending", "in_progress", "completed", "cancelled"]);
+
+function isTodoItem(v: unknown): v is TodoItem {
+  if (typeof v !== "object" || v === null) return false;
+  const o = v as Record<string, unknown>;
+  return typeof o.content === "string" && typeof o.status === "string" && STATUSES.has(o.status);
+}
+
+export function parseTodoPayload(payload: unknown): TodoData | null {
+  if (typeof payload !== "object" || payload === null) return null;
+  const obj = payload as Record<string, unknown>;
+  const raw = obj.todos;
+  if (!Array.isArray(raw)) return null;
+  const todos: TodoItem[] = [];
+  for (const entry of raw) {
+    if (!isTodoItem(entry)) return null;
+    todos.push(entry);
+  }
+  return { todos };
+}
+
+/** The `rendererId` the `todo` extension's `custom` surface field uses. */
+export const TODO_RENDERER_ID = "todo";