migration: establish exact preserved app baseline

app/static/shared/state.js

@@ -0,0 +1,44 @@
+(function exposeStateStore(global) {
+  "use strict";
+
+  function create(domains) {
+    const owners = new Map();
+    const stores = {};
+    Object.entries(domains).forEach(([domain, values]) => {
+      stores[domain] = { ...values };
+      Object.keys(values).forEach((key) => {
+        if (owners.has(key)) throw new Error(`Duplicate state field: ${key}`);
+        owners.set(key, domain);
+      });
+    });
+
+    const proxy = new Proxy({}, {
+      get(_target, key) {
+        if (key === "domain") return (name) => stores[name];
+        if (key === "domains") return Object.freeze({ ...stores });
+        if (typeof key !== "string" || !owners.has(key)) return undefined;
+        return stores[owners.get(key)][key];
+      },
+      set(_target, key, value) {
+        if (typeof key !== "string" || !owners.has(key)) {
+          throw new Error(`Unregistered application state field: ${String(key)}`);
+        }
+        stores[owners.get(key)][key] = value;
+        return true;
+      },
+      has(_target, key) {
+        return key === "domain" || key === "domains" || owners.has(key);
+      },
+      ownKeys() {
+        return [...owners.keys()];
+      },
+      getOwnPropertyDescriptor(_target, key) {
+        if (!owners.has(key)) return undefined;
+        return { enumerable: true, configurable: true };
+      },
+    });
+    return proxy;
+  }
+
+  global.XiaobaiState = Object.freeze({ create });
+})(window);