refactor(characters): drive shared UI from active character

src/app/splash/hooks/__tests__/use-splash-latest-message.test.tsx

@@ -26,6 +26,7 @@ import { useSplashLatestMessage } from "../use-splash-latest-message";
 
 function LatestMessageHarness() {
   const state = useSplashLatestMessage({
+    characterId: "character_maya",
     hasInitialized: true,
     isAuthLoading: false,
     loginStatus: "facebook",
@@ -64,5 +65,9 @@ describe("useSplashLatestMessage hydration", () => {
     expect(hydrationErrors).toEqual([]);
     expect(container.textContent).toBe("Loading");
     expect(mocks.loadLatestMessage).toHaveBeenCalledOnce();
+    expect(mocks.loadLatestMessage).toHaveBeenCalledWith({
+      cache: mocks.cache,
+      characterId: "character_maya",
+    });
   });
 });

src/app/splash/hooks/use-splash-latest-message.ts

@@ -3,7 +3,6 @@
 import { useEffect, useState } from "react";
 
 import type { LoginStatus } from "@/data/schemas/auth";
-import { DEFAULT_CHARACTER_ID } from "@/data/constants/character";
 import { useHasHydrated } from "@/hooks/use-has-hydrated";
 import { loadSplashLatestMessagePreview } from "@/lib/chat/splash_latest_message";
 import { useSplashLatestMessageCache } from "@/providers/splash-latest-message-provider";
@@ -13,7 +12,7 @@ import { Result } from "@/utils/result";
 const log = new Logger("SplashLatestMessage");
 
 export interface UseSplashLatestMessageInput {
-  characterId?: string;
+  characterId: string;
   hasInitialized: boolean;
   isAuthLoading: boolean;
   loginStatus: LoginStatus;
@@ -31,7 +30,7 @@ interface SplashLatestMessageState {
 }
 
 export function useSplashLatestMessage({
-  characterId = DEFAULT_CHARACTER_ID,
+  characterId,
   hasInitialized,
   isAuthLoading,
   loginStatus,