fix: harden mobile indexeddb persistence path

tests/dexie-loader.mjs

@@ -0,0 +1,37 @@
+import assert from "node:assert/strict";
+
+import { ensureDexieLoaded } from "../sync/bme-db.js";
+
+const previousDocument = globalThis.document;
+const previousDexie = globalThis.Dexie;
+const previousLoadPromise = globalThis.__stBmeDexieLoadPromise;
+
+try {
+  globalThis.document = {};
+  delete globalThis.Dexie;
+  delete globalThis.__stBmeDexieLoadPromise;
+
+  const DexieCtor = await ensureDexieLoaded();
+  assert.equal(typeof DexieCtor, "function");
+  assert.equal(globalThis.Dexie, DexieCtor);
+} finally {
+  if (previousDocument === undefined) {
+    delete globalThis.document;
+  } else {
+    globalThis.document = previousDocument;
+  }
+
+  if (previousDexie === undefined) {
+    delete globalThis.Dexie;
+  } else {
+    globalThis.Dexie = previousDexie;
+  }
+
+  if (previousLoadPromise === undefined) {
+    delete globalThis.__stBmeDexieLoadPromise;
+  } else {
+    globalThis.__stBmeDexieLoadPromise = previousLoadPromise;
+  }
+}
+
+console.log("dexie-loader tests passed");