fix: harden persistence tiers and opfs durability

tests/native-persist-delta-failopen.mjs

@@ -0,0 +1,53 @@
+import assert from "node:assert/strict";
+
+function moduleUrl(tag) {
+  return `../vendor/wasm/stbme_core.js?test=${Date.now()}-${tag}`;
+}
+
+globalThis.__stBmeDisableWasmPackArtifacts = true;
+delete globalThis.__stBmeLoadRustWasmLayout;
+
+const firstLoad = await import(moduleUrl("native-persist-first"));
+let firstError = "";
+try {
+  await firstLoad.installNativePersistDeltaHook();
+} catch (error) {
+  firstError = error?.message || String(error);
+}
+
+assert.match(
+  firstError,
+  /native module unavailable|native persist delta builder unavailable|global-loader|Rust\/WASM artifact is not initialized/i,
+);
+
+globalThis.__stBmeLoadRustWasmLayout = async () => ({
+  solve_layout() {
+    return {
+      ok: true,
+      positions: [],
+      diagnostics: {
+        solver: "mock-rust-wasm",
+      },
+    };
+  },
+  build_persist_delta() {
+    return {
+      upsertNodes: [],
+      upsertEdges: [],
+      deleteNodeIds: [],
+      deleteEdgeIds: [],
+      tombstones: [],
+      runtimeMetaPatch: {},
+    };
+  },
+});
+
+const retryStatus = await firstLoad.installNativePersistDeltaHook();
+assert.equal(retryStatus.loaded, true);
+assert.equal(typeof globalThis.__stBmeNativeBuildPersistDelta, "function");
+
+delete globalThis.__stBmeNativeBuildPersistDelta;
+delete globalThis.__stBmeLoadRustWasmLayout;
+delete globalThis.__stBmeDisableWasmPackArtifacts;
+
+console.log("native-persist-delta-failopen tests passed");