feat(offline): add IndexedDB schema for queue + cache

src/lib/offline/db.ts

@@ -0,0 +1,50 @@
+import { openDB, type DBSchema, type IDBPDatabase } from "idb";
+
+export interface QueuedAction {
+  id: string;                  // clientActionId (uuid v4)
+  actionName: string;          // e.g. "markOrderReady"
+  payload: unknown;            // JSON-serializable args
+  createdAt: number;           // Date.now()
+  attempts: number;            // sync attempts
+  lastAttemptAt: number | null;
+  status: "pending" | "in-flight" | "synced" | "conflict" | "failed";
+  error?: string;
+}
+
+interface RouteCommerceOfflineDB extends DBSchema {
+  queue: {
+    key: string;
+    value: QueuedAction;
+    indexes: { "by-status": string; "by-created": number };
+  };
+  cache: {
+    key: string;               // e.g. "orders:brandId:abc"
+    value: { key: string; data: unknown; cachedAt: number };
+  };
+}
+
+const DB_NAME = "route-commerce-offline";
+const DB_VERSION = 1;
+
+let dbPromise: Promise<IDBPDatabase<RouteCommerceOfflineDB>> | null = null;
+
+export function getOfflineDB(): Promise<IDBPDatabase<RouteCommerceOfflineDB>> {
+  if (typeof window === "undefined") {
+    throw new Error("getOfflineDB called on the server");
+  }
+  if (!dbPromise) {
+    dbPromise = openDB<RouteCommerceOfflineDB>(DB_NAME, DB_VERSION, {
+      upgrade(db) {
+        if (!db.objectStoreNames.contains("queue")) {
+          const queue = db.createObjectStore("queue", { keyPath: "id" });
+          queue.createIndex("by-status", "status");
+          queue.createIndex("by-created", "createdAt");
+        }
+        if (!db.objectStoreNames.contains("cache")) {
+          db.createObjectStore("cache", { keyPath: "key" });
+        }
+      },
+    });
+  }
+  return dbPromise;
+}