diff --git a/src/lib/persist.ts b/src/lib/persist.ts
new file mode 100644
index 0000000..675a068
--- /dev/null
+++ b/src/lib/persist.ts
@@ -0,0 +1,92 @@
+import { load, type Store } from "@tauri-apps/plugin-store";
+import { STORE_FILE, STORE_KEY, type OverlayPersistedState } from "../types/overlay";
+import { useOverlayStore } from "./store";
+import { debounce } from "./debounce";
+
+const DEFAULTS: OverlayPersistedState = {
+  url: "",
+  opacity: 1.0,
+  alwaysOnTop: true,
+  clickThrough: false,
+};
+
+let storePromise: Promise<Store> | null = null;
+function getStore(): Promise<Store> {
+  if (!storePromise) {
+    storePromise = load(STORE_FILE, { defaults: {}, autoSave: false });
+  }
+  return storePromise;
+}
+
+function isPersistedShape(v: unknown): v is OverlayPersistedState {
+  if (!v || typeof v !== "object") return false;
+  const o = v as Record<string, unknown>;
+  return (
+    typeof o.url === "string" &&
+    typeof o.opacity === "number" &&
+    typeof o.alwaysOnTop === "boolean" &&
+    typeof o.clickThrough === "boolean"
+  );
+}
+
+/** Load persisted state from disk and hydrate the Zustand store. Safe on first run. */
+export async function hydrateFromDisk(): Promise<void> {
+  try {
+    const s = await getStore();
+    const raw = await s.get<unknown>(STORE_KEY);
+    const value = isPersistedShape(raw) ? raw : DEFAULTS;
+    useOverlayStore.getState().hydrate(value);
+  } catch (err) {
+    console.warn("Failed to load persisted state; using defaults", err);
+    useOverlayStore.getState().hydrate(DEFAULTS);
+  }
+}
+
+// We persist on a 300ms debounce. The mirror below tracks "latest known
+// pending state" so a synchronous flush at beforeunload time has something
+// to issue — even though the actual write is unavoidably async.
+let latestPending: OverlayPersistedState | null = null;
+
+async function writeNow(state: OverlayPersistedState): Promise<void> {
+  try {
+    const s = await getStore();
+    await s.set(STORE_KEY, state);
+    await s.save();
+  } catch (err) {
+    console.warn("Failed to persist state", err);
+  }
+}
+
+const writeDebounced = debounce((state: OverlayPersistedState): void => {
+  latestPending = null;
+  void writeNow(state);
+}, 300);
+
+/** Subscribe to store changes and persist the four user-pref fields. */
+export function startPersistSubscription(): () => void {
+  return useOverlayStore.subscribe((s) => {
+    const snapshot: OverlayPersistedState = {
+      url: s.url,
+      opacity: s.opacity,
+      alwaysOnTop: s.alwaysOnTop,
+      clickThrough: s.clickThrough,
+    };
+    latestPending = snapshot;
+    writeDebounced(snapshot);
+  });
+}
+
+/**
+ * Best-effort synchronous flush for beforeunload. The actual disk write is
+ * unavoidably async — we fire-and-forget it. If the window is destroyed
+ * before the write lands, the prior debounce-tick's value (at most 300ms
+ * stale) will be loaded next session. That bounded staleness is the
+ * accepted trade-off for a Phase 1 utility app.
+ */
+export function flushPendingPersistSync(): void {
+  if (latestPending === null) return;
+  const snapshot = latestPending;
+  latestPending = null;
+  writeDebounced.cancel();
+  void writeNow(snapshot);
+}