The stub path checks the room id, as the ledger path does

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

packages/server/src/store.ts

@@ -150,7 +150,10 @@ export function ledgerStat(roomId: string): { bytes: number; mtimeMs: number } |
 // the room's whole truth and the room stays asleep, unreplayed.
 
 const stubDir = () => join(DATA_DIR, "..", "stubs");
-const stubFor = (roomId: string) => join(stubDir(), `${roomId}.json`);
+function stubFor(roomId: string): string {
+  if (!safeRoomId(roomId)) throw new Error(`unsafe room id: ${JSON.stringify(roomId)}`);
+  return join(stubDir(), `${roomId}.json`);
+}
 
 export function readStubFile<T>(roomId: string): { bytes: number; stub: T } | null {
   if (!safeRoomId(roomId)) return null;