feat: add reading settings sync

lib/reading-prefs.ts

@@ -0,0 +1,53 @@
+/**
+ * Browser-side client for the user's roaming reading preferences.
+ *
+ * The BFF stores prefs as opaque JSONB keyed off the user. This module
+ * just round-trips that blob — it makes no claim about its shape (that
+ * contract is owned by components/reading-settings.tsx). All calls run
+ * with `credentials: "include"` so the auth cookie comes along.
+ */
+
+const BFF_BASE =
+  process.env.NEXT_PUBLIC_BFF_URL || "http://localhost:8080";
+
+type Envelope<T> = {
+  success?: boolean;
+  data?: T;
+  error?: { code: number; message: string };
+};
+
+async function call<T>(path: string, init?: RequestInit): Promise<T | null> {
+  const res = await fetch(`${BFF_BASE}/api/v1${path}`, {
+    credentials: "include",
+    headers: { "Content-Type": "application/json", ...(init?.headers ?? {}) },
+    ...init,
+  });
+  if (res.status === 401 || res.status === 403) return null;
+  if (!res.ok) {
+    throw new Error(`reading-prefs ${path}: ${res.status}`);
+  }
+  const body = (await res.json().catch(() => ({}))) as Envelope<T>;
+  return (body.data ?? null) as T | null;
+}
+
+export const readingPrefsApi = {
+  /** Fetches the caller's reading prefs blob. Returns `null` if the
+   *  request is unauthenticated (treat as "no remote prefs"). The blob
+   *  is the raw JSON object the frontend wrote last; an empty object
+   *  on first load. */
+  async get(): Promise<Record<string, unknown> | null> {
+    const data = await call<Record<string, unknown>>("/users/me/reading-prefs");
+    return data ?? null;
+  },
+
+  /** Overwrites the caller's reading prefs blob. The server stores the
+   *  payload verbatim (after canonicalising via re-marshal) — schema is
+   *  client-owned. Errors are swallowed by the caller; reading prefs
+   *  should never block a UI interaction. */
+  async put(prefs: Record<string, unknown>): Promise<void> {
+    await call<Record<string, unknown>>("/users/me/reading-prefs", {
+      method: "PUT",
+      body: JSON.stringify(prefs),
+    });
+  },
+};