fix: harden persistence tiers and opfs durability

tests/opfs-meta-fast-path.mjs

@@ -0,0 +1,72 @@
+import assert from "node:assert/strict";
+
+import {
+  BME_GRAPH_LOCAL_STORAGE_MODE_OPFS_SHADOW,
+  OpfsGraphStore,
+} from "../sync/bme-opfs-store.js";
+import { createMemoryOpfsRoot } from "./helpers/memory-opfs.mjs";
+
+const rootDirectory = createMemoryOpfsRoot();
+const store = new OpfsGraphStore("chat-opfs-meta-fast-path", {
+  rootDirectoryFactory: async () => rootDirectory,
+  storeMode: BME_GRAPH_LOCAL_STORAGE_MODE_OPFS_SHADOW,
+});
+
+await store.open();
+await store.importSnapshot(
+  {
+    meta: {
+      revision: 3,
+      lastBackupFilename: "before.json",
+      lastSyncUploadedAt: 10,
+    },
+    state: {
+      lastProcessedFloor: 2,
+      extractionCount: 1,
+    },
+    nodes: [
+      {
+        id: "node-1",
+        type: "event",
+        fields: { title: "A" },
+        archived: false,
+        updatedAt: 1,
+      },
+    ],
+    edges: [],
+    tombstones: [],
+  },
+  {
+    mode: "replace",
+    preserveRevision: true,
+  },
+);
+
+const originalLoadSnapshot = store._loadSnapshot.bind(store);
+let loadSnapshotCalls = 0;
+store._loadSnapshot = async (...args) => {
+  loadSnapshotCalls += 1;
+  return await originalLoadSnapshot(...args);
+};
+
+assert.equal(await store.getMeta("lastBackupFilename", ""), "before.json");
+assert.equal(await store.getRevision(), 3);
+await store.patchMeta({
+  lastBackupFilename: "after.json",
+  lastProcessedFloor: 9,
+  extractionCount: 4,
+});
+
+assert.equal(
+  loadSnapshotCalls,
+  0,
+  "manifest-only meta fast path should not load full snapshot",
+);
+
+const snapshot = await originalLoadSnapshot();
+assert.equal(snapshot.meta.lastBackupFilename, "after.json");
+assert.equal(snapshot.state.lastProcessedFloor, 9);
+assert.equal(snapshot.state.extractionCount, 4);
+assert.equal(snapshot.nodes.length, 1);
+
+console.log("opfs-meta-fast-path tests passed");