feat: chat reactions

lib/chat.ts

@@ -119,6 +119,8 @@ export type ChatMessage = {
   reply_to?: ReplyPreview | null;
   /** Always an array — media, link cards and shared entities. */
   attachments: Attachment[];
+  /** Emoji chips, grouped with counts. `mine` marks the viewer's own. */
+  reactions: Reaction[];
   /**
    * Client-only. Set on a message shown optimistically before the server has
    * acknowledged it; never sent by the BFF.
@@ -171,6 +173,21 @@ export type AttachmentKind =
   | "entity"
   | "quote";
 
+/** One emoji on a message, grouped across everyone who chose it. */
+export type Reaction = {
+  emoji: string;
+  count: number;
+  /** The viewer's own choice — highlight the chip, and tapping it removes. */
+  mine: boolean;
+};
+
+/** One person's reaction, for the "who reacted" list. */
+export type ReactionDetail = {
+  user: ChatPeer;
+  emoji: string;
+  created_at: string;
+};
+
 export type Attachment = {
   id: string;
   message_id: string;
@@ -411,6 +428,40 @@ export const chat = {
       body: JSON.stringify({ seq }),
     }),
 
+  /** One hydrated message — reaction counts are per viewer, so a client told
+   *  "message X changed" has to ask rather than compute. */
+  message: (conversationId: string, messageId: string) =>
+    call<ChatMessage>(
+      `/chat/conversations/${conversationId}/messages/${messageId}`,
+    ),
+
+  /** Tell the thread someone is composing. Ephemeral — nothing is stored. */
+  typing: (conversationId: string) =>
+    call<void>(`/chat/conversations/${conversationId}/typing`, {
+      method: "POST",
+    }),
+
+  /** Who reacted, and with what. Only fetched when the list is opened —
+   *  the thread renders from the grouped counts on each message. */
+  reactionDetails: (conversationId: string, messageId: string) =>
+    call<ReactionDetail[]>(
+      `/chat/conversations/${conversationId}/messages/${messageId}/reactions`,
+    ),
+
+  /** Set the caller's reaction, replacing any previous one. */
+  react: (conversationId: string, messageId: string, emoji: string) =>
+    call<void>(
+      `/chat/conversations/${conversationId}/messages/${messageId}/reaction`,
+      { method: "PUT", body: JSON.stringify({ emoji }) },
+    ),
+
+  /** Remove the caller's reaction. Idempotent. */
+  unreact: (conversationId: string, messageId: string) =>
+    call<void>(
+      `/chat/conversations/${conversationId}/messages/${messageId}/reaction`,
+      { method: "DELETE" },
+    ),
+
   markDelivered: (conversationId: string, seq: number) =>
     call<void>(`/chat/conversations/${conversationId}/delivered`, {
       method: "POST",