push updated state to clients over SSE (ISS-129)

lib/db/client.ts

@@ -211,12 +211,14 @@ export async function persist(instance: GameDb): Promise<void> {
   await fs.rename(tmp, instance.file);
 }
 
-// Singleton for the app process; openGameDb() is the uncached variant (tests).
-let ready: Promise<GameDb> | null = null;
+// Singleton for the app process; openGameDb() is the uncached variant (tests). ISS-129 (v0.57.0):
+// lives on globalThis because Next.js can load this module more than once per process —
+// instrumentation.ts and route handlers get separate module instances, so a plain `let` would give
+// each its own in-memory sql.js DB (both persisting to the same file). One world per process.
+const g = globalThis as unknown as { __flightGameDb?: Promise<GameDb> };
 
 export function getGameDb(): Promise<GameDb> {
-  if (!ready) ready = open(defaultDbPath());
-  return ready;
+  return (g.__flightGameDb ??= open(defaultDbPath()));
 }
 
 export async function openGameDb(file: string): Promise<GameDb> {