fix: thread accountId through subagent announce delivery

Co-authored-by: Adam Holt <adam91holt@users.noreply.github.com>

src/utils/account-id.ts

@@ -0,0 +1,5 @@
+export function normalizeAccountId(value?: string): string | undefined {
+  if (typeof value !== "string") return undefined;
+  const trimmed = value.trim();
+  return trimmed || undefined;
+}

src/utils/delivery-context.ts

@@ -0,0 +1,21 @@
+import { normalizeAccountId } from "./account-id.js";
+
+export type DeliveryContext = {
+  channel?: string;
+  to?: string;
+  accountId?: string;
+};
+
+export function normalizeDeliveryContext(context?: DeliveryContext): DeliveryContext | undefined {
+  if (!context) return undefined;
+  const channel =
+    typeof context.channel === "string" ? context.channel.trim() : undefined;
+  const to = typeof context.to === "string" ? context.to.trim() : undefined;
+  const accountId = normalizeAccountId(context.accountId);
+  if (!channel && !to && !accountId) return undefined;
+  return {
+    channel: channel || undefined,
+    to: to || undefined,
+    accountId,
+  };
+}