diff --git a/CLAUDE.md b/CLAUDE.md
index 9370c09..ed82000 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -109,10 +109,14 @@ for the React-side bridge code.
 - **`SessionDataManager.getUserData(id)` does NOT exist.** Some legacy
   code in the React client used it under a `getUserData ?` truthy guard;
   the branch was always dead. Only `getUserDataSnapshot()` exists.
-- `IRoomSession.sendChatMessage` / `sendShoutMessage` require **3 args**
-  (text, styleId, chatColour). The React client's chat-input legacy
-  passes 2 — known pre-existing gap, do not "fix" the client without
-  also threading chatColour through the chat composer pipeline.
+- `IRoomSession.sendChatMessage` / `sendShoutMessage` accept an optional
+  `chatColour` 3rd arg (was required pre-2.1.1, now optional to match
+  the historical call sites in the React client). The implementation
+  forwards `undefined` to the composer just fine; pass a value only when
+  you need a specific bubble colour.
+- `IRoomSession.password` and `IRoomSession.sendBackgroundMessage` are
+  now part of the public interface (they always existed on the
+  implementation class — interface caught up).
 - The renderer is **synchronous**: `EventDispatcher.dispatchEvent` is a
   synchronous loop over listeners. Don't add `await` inside the
   `processEvent` loop — it would change ordering guarantees that
diff --git a/packages/api/src/nitro/session/IRoomSession.ts b/packages/api/src/nitro/session/IRoomSession.ts
index 02a905e..d12ad5a 100644
--- a/packages/api/src/nitro/session/IRoomSession.ts
+++ b/packages/api/src/nitro/session/IRoomSession.ts
@@ -9,10 +9,11 @@ export interface IRoomSession
     setRoomOwner(): void;
     start(): boolean;
     reset(roomId: number): void;
-    sendChatMessage(text: string, styleId: number, chatColour: string): void;
-    sendShoutMessage(text: string, styleId: number, chatColour: string): void;
+    sendChatMessage(text: string, styleId: number, chatColour?: string): void;
+    sendShoutMessage(text: string, styleId: number, chatColour?: string): void;
     sendWhisperMessage(recipientName: string, text: string, styleId: number): void;
     sendChatTypingMessage(isTyping: boolean): void;
+    sendBackgroundMessage(backgroundImage: number, backgroundStand: number, backgroundOverlay: number, backgroundCard?: number): void;
     sendMottoMessage(motto: string): void;
     sendDanceMessage(danceId: number): void;
     sendExpressionMessage(expression: number): void;
@@ -50,6 +51,7 @@ export interface IRoomSession
     sendScriptProceed(): void;
     userDataManager: IUserDataManager;
     roomId: number;
+    password: string;
     state: string;
     tradeMode: number;
     isPrivateRoom: boolean;