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diff --git a/src/ark/store.js b/src/ark/store.js
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+// Ark state storage: IndexedDB with the coins' signed bytes as raw
+// Uint8Arrays, fronted by an in-memory copy so every read and write the app
+// makes stays synchronous (the render path reads it, the manager saves it).
+//
+// Why not localStorage: a deep coin set is ~700KB of JSON, which localStorage
+// holds as UTF-16 and hands back as a string — every boot parsed it, every
+// save stringified it (several times, ~100ms each on a phone). IndexedDB
+// structured-clones the object as-is, bytes stay bytes, and the write is
+// write-behind: coalesced and asynchronous, flushed immediately when the page
+// hides so nothing is lost to a suspend.
+//
+// Records keep today's localStorage keys (`btc-wallet-cache:<id>:ark…`) so
+// the wallet-wipe prefix logic still applies. Existing localStorage copies
+// migrate on first open (newest `_rev` wins) and are removed only after the
+// IndexedDB write completed. If IndexedDB is unavailable the store falls
+// back to localStorage exactly as before.
+
+import { vtxoBytesToStr, vtxoBytesFromStr } from './proto.js';
+
+const DB = 'coinos-ark';
+const STORE = 'states';
+const VERSION = 1;
+export const ARK_KEY_RE = /^btc-wallet-cache:[0-9a-f]+:ark(:|$)/;
+const DEBOUNCE_MS = 200;
+
+// ---- backends ------------------------------------------------------------
+export function idbBackend() {
+  if (typeof indexedDB === 'undefined') return null;
+  let dbp = null;
+  const open = () => {
+    if (dbp) return dbp;
+    dbp = new Promise((resolve, reject) => {
+      const req = indexedDB.open(DB, VERSION);
+      req.onupgradeneeded = () => { const db = req.result; if (!db.objectStoreNames.contains(STORE)) db.createObjectStore(STORE); };
+      req.onsuccess = () => {
+        const db = req.result;
+        db.onversionchange = () => { try { db.close(); } catch {} dbp = null; };
+        db.onclose = () => { dbp = null; };
+        resolve(db);
+      };
+      req.onerror = () => { dbp = null; reject(req.error); };
+      req.onblocked = () => { dbp = null; reject(new Error('IndexedDB blocked')); };
+    });
+    return dbp;
+  };
+  const run = async (mode, fn) => {
+    const db = await open();
+    return new Promise((resolve, reject) => {
+      const t = db.transaction(STORE, mode);
+      let out;
+      try { out = fn(t.objectStore(STORE)); } catch (e) { reject(e); return; }
+      t.oncomplete = () => resolve(out && typeof out.then === 'function' ? undefined : out);
+      t.onerror = () => reject(t.error);
+      t.onabort = () => reject(t.error || new Error('aborted'));
+    });
+  };
+  return {
+    async list() {
+      const db = await open();
+      return new Promise((resolve, reject) => {
+        const t = db.transaction(STORE, 'readonly');
+        const s = t.objectStore(STORE);
+        const keys = s.getAllKeys(), vals = s.getAll();
+        t.oncomplete = () => resolve(keys.result.map((k, i) => [k, vals.result[i]]));
+        t.onerror = () => reject(t.error);
+      });
+    },
+    write(puts, dels) {
+      if (!puts.length && !dels.length) return Promise.resolve();
+      return run('readwrite', (s) => { for (const [k, v] of puts) s.put(v, k); for (const k of dels) s.delete(k); });
+    },
+  };
+}
+// For tests: the same contract over a Map.
+export function memoryBackend(initial = []) {
+  const m = new Map(initial);
+  return {
+    writes: 0,
+    async list() { return [...m]; },
+    async write(puts, dels) { this.writes++; for (const [k, v] of puts) m.set(k, structuredClone(v)); for (const k of dels) m.delete(k); },
+    dump() { return m; },
+  };
+}
+
+// ---- on-disk shape: coins' bytes as raw bytes -------------------------------
+function toDisk(v) {
+  if (!v || !Array.isArray(v.vtxos)) return v;
+  return { ...v, vtxos: v.vtxos.map((x) => (typeof x.bytes === 'string' ? { ...x, bytes: vtxoBytesFromStr(x.bytes) } : x)) };
+}
+function fromDisk(v) {
+  if (!v || !Array.isArray(v.vtxos)) return v;
+  return { ...v, vtxos: v.vtxos.map((x) => (x.bytes instanceof Uint8Array ? { ...x, bytes: vtxoBytesToStr(x.bytes) } : x)) };
+}
+const clone = (v) => (typeof structuredClone === 'function' ? structuredClone(v) : JSON.parse(JSON.stringify(v)));
+
+// ---- the store ---------------------------------------------------------------
+export class ArkStore {
+  constructor({ backend = idbBackend(), ls = () => globalThis.localStorage, now = Date.now } = {}) {
+    this.backend = backend;   // null → localStorage mode (today's behaviour)
+    this.ls = ls;
+    this.now = now;
+    this.mem = new Map();
+    this.dirty = new Set();
+    this.ready = !backend;    // localStorage mode needs no opening
+    this.timer = 0;
+    this.opening = null;
+    this._flushing = null;
+    if (typeof document !== 'undefined') {
+      document.addEventListener('visibilitychange', () => { if (document.visibilityState === 'hidden') this.flush(); });
+      addEventListener('pagehide', () => this.flush());
+    }
+  }
+  get lsMode() { return !this.backend; }
+
+  // Load everything into memory, then fold in (and later retire) any
+  // localStorage copies. The fold-in is synchronous after the async read, so
+  // no write can slip between "what localStorage held" and "ready".
+  open() {
+    if (this.ready) return Promise.resolve();
+    if (this.opening) return this.opening;
+    this.opening = (async () => {
+      let rows;
+      try { rows = await this.backend.list(); } catch (e) {
+        this.backend = null; this.ready = true; // IndexedDB refused: stay on localStorage
+        return;
+      }
+      for (const [k, v] of rows) this.mem.set(k, fromDisk(v));
+      const migrated = [];
+      const ls = this.ls();
+      if (ls) {
+        for (let i = 0; i < ls.length; i++) {
+          const k = ls.key(i);
+          if (!k || !ARK_KEY_RE.test(k)) continue;
+          let v; try { v = JSON.parse(ls.getItem(k)); } catch { continue; }
+          if (!v || typeof v !== 'object') continue;
+          const cur = this.mem.get(k);
+          if (!cur || (v._rev || 0) >= (cur._rev || 0)) { this.mem.set(k, v); this.dirty.add(k); }
+          migrated.push(k);
+        }
+      }
+      this.ready = true;
+      if (migrated.length) {
+        this.flush().then(() => { for (const k of migrated) { try { ls.removeItem(k); } catch {} } }).catch(() => {});
+      }
+    })();
+    return this.opening;
+  }
+
+  get(key) {
+    if (!this.ready || this.lsMode) {
+      try { const raw = this.ls().getItem(key); return raw ? JSON.parse(raw) : null; } catch { return null; }
+    }
+    const v = this.mem.get(key);
+    return v ? clone(v) : null;
+  }
+  set(key, obj) {
+    if (!this.ready || this.lsMode) { try { this.ls().setItem(key, JSON.stringify(obj)); } catch {} return; }
+    this.mem.set(key, obj);
+    this.dirty.add(key);
+    this._schedule();
+  }
+  remove(key) {
+    if (!this.ready || this.lsMode) { try { this.ls().removeItem(key); } catch {} return; }
+    this.mem.delete(key);
+    this.dirty.add(key);
+    this._schedule();
+  }
+  keys(prefix = '') {
+    if (!this.ready || this.lsMode) {
+      const out = []; const ls = this.ls();
+      try { for (let i = 0; i < ls.length; i++) { const k = ls.key(i); if (k && k.startsWith(prefix) && ARK_KEY_RE.test(k)) out.push(k); } } catch {}
+      return out;
+    }
+    return [...this.mem.keys()].filter((k) => k.startsWith(prefix));
+  }
+  // Wallet wipe: everything under the wallet's cache-key prefix, wherever it lives.
+  removePrefix(prefix) {
+    for (const k of this.keys(prefix)) this.remove(k);
+    const ls = this.ls();
+    try {
+      const gone = [];
+      for (let i = 0; i < ls.length; i++) { const k = ls.key(i); if (k && k.startsWith(prefix) && ARK_KEY_RE.test(k)) gone.push(k); }
+      for (const k of gone) ls.removeItem(k);
+    } catch {}
+  }
+
+  _schedule() {
+    const hidden = typeof document !== 'undefined' && document.visibilityState === 'hidden';
+    if (hidden) { this.flush(); return; }
+    if (this.timer) return;
+    this.timer = setTimeout(() => { this.timer = 0; this.flush(); }, DEBOUNCE_MS);
+  }
+  // Write every dirty key in one transaction. A failed write keeps the keys
+  // dirty for the next attempt; the in-memory copy is always authoritative.
+  flush() {
+    if (this.timer) { clearTimeout(this.timer); this.timer = 0; }
+    if (!this.ready || this.lsMode || !this.dirty.size) return this._flushing || Promise.resolve();
+    if (this._flushing) return this._flushing.then(() => this.flush());
+    const keys = [...this.dirty]; this.dirty.clear();
+    const puts = [], dels = [];
+    for (const k of keys) { if (this.mem.has(k)) puts.push([k, toDisk(this.mem.get(k))]); else dels.push(k); }
+    this._flushing = this.backend.write(puts, dels)
+      .catch(() => { for (const k of keys) this.dirty.add(k); })
+      .finally(() => { this._flushing = null; });
+    return this._flushing;
+  }
+}
+
+let shared = null;
+export function arkStore() {
+  if (!shared) { shared = new ArkStore(); shared.open().catch(() => {}); }
+  return shared;
+}