fix: chat accepts posts

lib/chat.ts

@@ -188,6 +188,25 @@ export type Attachment = {
   description?: string | null;
   site_name?: string | null;
   image_url?: string | null;
+
+  /** Shared entity. `entity` is resolved per viewer on every read, so it can
+   *  be absent even though the message still references a post. */
+  entity_type?: "post" | null;
+  entity_id?: string | null;
+  entity?: SharedPost | null;
+  /** The post was deleted, hidden, or is no longer visible to this viewer. */
+  entity_unavailable?: boolean;
+};
+
+/** The post card the BFF resolves for a shared-post attachment. */
+export type SharedPost = {
+  id: string;
+  author_handle: string;
+  author_name: string;
+  author_avatar_url?: string | null;
+  caption: string;
+  image_url?: string | null;
+  source_title?: string;
 };
 
 /** How two people in a DM stand with each other. */
@@ -261,6 +280,8 @@ export const chat = {
       previewUrl?: string;
       attachments?: UploadedAttachment[];
       quote?: QuotePayload;
+      /** Share a post as a card. Only the reference — the BFF resolves it. */
+      entity?: { type: "post"; id: string };
     },
   ) =>
     call<ChatMessage>(`/chat/conversations/${conversationId}/messages`, {
@@ -273,6 +294,7 @@ export const chat = {
         preview_url: opts?.previewUrl ?? null,
         attachments: opts?.attachments ?? [],
         quote: opts?.quote ?? null,
+        entity: opts?.entity ?? null,
       }),
     }),