Gateway: show subagent requests on the parent's card, and settle threads

gateway/src/contract.ts

@@ -105,6 +105,11 @@ export interface FeedItem {
   /** The agent's latest message, trimmed for the watch. Null until the gateway has read it. */
   lastMessage: string | null;
   request: PendingRequest | null;
+  /**
+   * Set when `request` comes from a subagent this thread delegated to, rather than the thread
+   * itself. Answer the request on that thread. `phase` is then the subagent's.
+   */
+  via: { hostId: string; threadId: string; title: string } | null;
 }
 
 /** Counts for the watch face complication. Cheap: no thread pages are read. */