Prefetch all the things!

frontend/src/prefetch.ts

@@ -0,0 +1,26 @@
+/**
+ * Consume prefetched API promises started in index.html before React loaded.
+ *
+ * Each key is consumed at most once — the first caller gets the promise,
+ * subsequent callers get undefined and should fall back to a normal fetch.
+ */
+
+import type { AppSettings, Channel, Contact, RadioConfig, UnreadCounts } from './types';
+
+interface PrefetchMap {
+  config?: Promise<RadioConfig>;
+  settings?: Promise<AppSettings>;
+  channels?: Promise<Channel[]>;
+  contacts?: Promise<Contact[]>;
+  unreads?: Promise<UnreadCounts>;
+  undecryptedCount?: Promise<{ count: number }>;
+}
+
+const store: PrefetchMap = (window as unknown as { __prefetch?: PrefetchMap }).__prefetch ?? {};
+
+/** Take a prefetched promise (consumed once, then gone). */
+export function takePrefetch<K extends keyof PrefetchMap>(key: K): PrefetchMap[K] {
+  const p = store[key];
+  delete store[key];
+  return p;
+}