feat(client): device pairing flow (v2.2.0-alpha3)

Completes PR #3 of the multi-device roadmap. Two devices of the same
identity can now be linked via a six-digit code + relay envelope
handshake. Chain-level fan-out (alpha2) and self-wipe on revoke (this
release, earlier commit) already work end-to-end.

New device — app/(auth)/pair.tsx:
  * Generates fresh X25519 keypair + six-digit code locally.
  * Displays them for transcription on the primary device.
  * Polls /relay/inbox on its own x25519 pub every 2.5s.
  * Decrypts each envelope with the session priv + sender_pub.
  * Accepts only payloads where {v=1, type=pair-handshake, code matches}.
  * On success, assembles a KeyFile (master Ed25519 from envelope,
    x25519 from session) and redirects into (app).

Primary device — app/(app)/devices.tsx:
  * "Link new device" opens a modal asking for {code, device key, name}.
  * On submit: builds+submits LINK_DEVICE tx for the new pub, then
    sends a one-shot relay envelope carrying {master_pub, master_priv,
    master_x25519_pub, code} encrypted for the new device's x25519 pub.
  * Optimistic local insert so the new row appears immediately.

Entry point — app/index.tsx:
  * Third button on welcome slide 3: "Pair". Routes to /auth/pair.
    Create / Import remain unchanged for fresh identities.

Security:
  * Master Ed25519 priv leaves the source device ONLY inside an envelope
    sealed with NaCl box for the new device's X25519 pub. The relay node
    sees only ciphertext.
  * Six-digit code (~20 bits) gates acceptance — an attacker who guesses
    both a session pub AND the code is still filtered by the X25519
    decryption itself (code match is belt-and-suspenders).
  * Envelope stays in relay mailbox until TTL — no DELETE call yet;
    idempotent on our side (saveKeyFile overwrites, session pub
    never polled after redirect).

Known trade-offs:
  * Manual transcription of a 64-char hex key is ugly. Alpha4 will
    offer a QR fallback on phones with cameras; desktop keeps typing.
  * No rate limit on the polling. Fine for a 1-minute handshake, needs
    cap-on-stale if a user leaves the screen open.

blockchain/chain.go

@@ -54,6 +54,9 @@ const (
 	prefixRelay         = "relay:"         // relay:<node_pubkey> → RegisterRelayPayload JSON
 	prefixRelayHB       = "relayhb:"       // relayhb:<node_pubkey> → unix seconds (int64) of last HB
 	prefixRelayProof    = "relayproof:"    // relayproof:<envelopeID> → claimant node_pubkey (1 claim per envelope)
+	// Multi-device registry (v2.2.0)
+	prefixDevice          = "device:"        // device:<x25519_pub> → DeviceRecord JSON
+	prefixDevicesByOwner  = "devicesbyowner:" // devicesbyowner:<master_pub>:<x25519_pub> → "" (reverse index for O(k) listing)
 	prefixContactIn     = "contact_in:"    // contact_in:<targetPub>:<requesterPub> → contactRecord JSON
 	prefixValidator     = "validator:"     // validator:<pubkey> → "" (presence = active)
 	prefixContract      = "contract:"      // contract:<contractID> → ContractRecord JSON
@@ -771,6 +774,99 @@ func PayChanCloseSigPayload(channelID string, balanceA, balanceB, nonce uint64)
 	return payChanCloseSigPayload(channelID, balanceA, balanceB, nonce)
 }
 
+// DevicesOf returns the active (non-revoked) device records for a master
+// identity. Sender fan-out reads this to decide how many envelopes to
+// produce per outgoing message. Empty slice (not error) for identities
+// with no registry entries yet — caller should fall back to the legacy
+// single-X25519 path via IdentityInfo.
+func (c *Chain) DevicesOf(masterPub string) ([]DeviceRecord, error) {
+	var out []DeviceRecord
+	err := c.db.View(func(txn *badger.Txn) error {
+		prefix := []byte(prefixDevicesByOwner + masterPub + ":")
+		it := txn.NewIterator(badger.IteratorOptions{Prefix: prefix, PrefetchValues: false})
+		defer it.Close()
+		for it.Rewind(); it.Valid(); it.Next() {
+			key := it.Item().KeyCopy(nil)
+			// key layout: devicesbyowner:<master>:<x25519> — take the suffix
+			x25519Pub := string(key[len(prefix):])
+			recItem, err := txn.Get([]byte(prefixDevice + x25519Pub))
+			if err != nil {
+				// Reverse index points to a missing record — stale entry,
+				// skip silently (shouldn't happen unless the DB was tampered
+				// with, but we don't want to fail the whole call).
+				continue
+			}
+			var rec DeviceRecord
+			if verr := recItem.Value(func(v []byte) error {
+				return json.Unmarshal(v, &rec)
+			}); verr != nil {
+				continue
+			}
+			if rec.RevokedAt != 0 {
+				continue
+			}
+			out = append(out, rec)
+		}
+		return nil
+	})
+	return out, err
+}
+
+// countActiveDevicesForOwner walks the reverse index (entries there are,
+// by construction, non-revoked — UNLINK_DEVICE deletes the index row).
+// O(k) where k = active device count, bounded by MaxDevicesPerOwner.
+func (c *Chain) countActiveDevicesForOwner(txn *badger.Txn, masterPub string) (int, error) {
+	prefix := []byte(prefixDevicesByOwner + masterPub + ":")
+	it := txn.NewIterator(badger.IteratorOptions{Prefix: prefix, PrefetchValues: false})
+	defer it.Close()
+	n := 0
+	for it.Rewind(); it.Valid(); it.Next() {
+		n++
+	}
+	return n, nil
+}
+
+// validateDevicePubKey checks the wire-level format of a device X25519
+// public key: 64 hex characters (32 bytes). Does NOT check that the key
+// is a valid curve point — senders learn that at encrypt time, and an
+// invalid point there just yields garbage ciphertext which the device
+// can't decrypt (self-punishing).
+func validateDevicePubKey(hexPub string) error {
+	if len(hexPub) != 64 {
+		return fmt.Errorf("x25519_pub_key must be 64 hex chars (got %d)", len(hexPub))
+	}
+	// Enforce strict lowercase-hex to keep keys canonical across clients —
+	// two clients hashing the same bytes with different letter cases would
+	// produce different registry lookups, which breaks sender fan-out.
+	for _, r := range hexPub {
+		switch {
+		case r >= '0' && r <= '9':
+		case r >= 'a' && r <= 'f':
+		default:
+			return fmt.Errorf("x25519_pub_key must be lowercase hex")
+		}
+	}
+	return nil
+}
+
+// validateDeviceName enforces the UX constraint that device labels stay
+// short and printable — this field gets displayed in Settings → Devices
+// and has no business carrying newlines, control chars, or 2KB blobs.
+func validateDeviceName(name string) error {
+	if name == "" {
+		return fmt.Errorf("device_name is required")
+	}
+	if len(name) > MaxDeviceNameLen {
+		return fmt.Errorf("device_name %d bytes > max %d", len(name), MaxDeviceNameLen)
+	}
+	for _, r := range name {
+		if r < 0x20 || r == 0x7f {
+			return fmt.Errorf("device_name contains a control character")
+		}
+	}
+	return nil
+}
+
 // Reputation returns the reputation stats for a public key.
 func (c *Chain) Reputation(pubKeyHex string) (RepStats, error) {
 	var r RepStats
@@ -1261,6 +1357,127 @@ func (c *Chain) applyTx(txn *badger.Txn, tx *Transaction) (uint64, error) {
 			return 0, err
 		}
 
+	case EventLinkDevice:
+		// Master Ed25519 (= tx.From) publishes a per-device X25519 pub.
+		// Validation:
+		//   1. Payload well-formed, X25519 pub is hex(32 bytes).
+		//   2. Device name is short + printable.
+		//   3. X25519 pub isn't already registered to a DIFFERENT owner.
+		//   4. Same owner re-linking the same pub is a no-op refresh
+		//      (updates device_name / added_at — useful for rename).
+		//   5. Owner has < MaxDevicesPerOwner active (non-revoked) devices.
+		//
+		// Fee: standard tx.Fee is debited from master's balance — cheap
+		// anti-spam. Block validation already enforced `tx.Fee >= MinFee`.
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("LINK_DEVICE debit: %w", err)
+		}
+		var p LinkDevicePayload
+		if err := json.Unmarshal(tx.Payload, &p); err != nil {
+			return 0, fmt.Errorf("%w: LINK_DEVICE bad payload: %v", ErrTxFailed, err)
+		}
+		if err := validateDevicePubKey(p.X25519PubKey); err != nil {
+			return 0, fmt.Errorf("%w: LINK_DEVICE: %v", ErrTxFailed, err)
+		}
+		if err := validateDeviceName(p.DeviceName); err != nil {
+			return 0, fmt.Errorf("%w: LINK_DEVICE: %v", ErrTxFailed, err)
+		}
+		devKey := []byte(prefixDevice + p.X25519PubKey)
+		if item, err := txn.Get(devKey); err == nil {
+			var existing DeviceRecord
+			if verr := item.Value(func(v []byte) error {
+				return json.Unmarshal(v, &existing)
+			}); verr == nil {
+				if existing.Owner != tx.From {
+					return 0, fmt.Errorf("%w: LINK_DEVICE: x25519 pub already linked to a different owner",
+						ErrTxFailed)
+				}
+				// Same owner — rename/refresh path. Keep AddedAt.
+				existing.DeviceName = p.DeviceName
+				existing.RevokedAt = 0 // re-link cancels a previous revoke
+				refreshed, _ := json.Marshal(existing)
+				if err := txn.Set(devKey, refreshed); err != nil {
+					return 0, err
+				}
+				// Restore reverse index too — UNLINK_DEVICE deletes it, so
+				// a re-link after revoke must recreate it or DevicesOf
+				// will skip the record.
+				idxKey := []byte(prefixDevicesByOwner + tx.From + ":" + p.X25519PubKey)
+				if err := txn.Set(idxKey, []byte{}); err != nil {
+					return 0, err
+				}
+				break
+			}
+		}
+		// Count owner's active devices.
+		active, err := c.countActiveDevicesForOwner(txn, tx.From)
+		if err != nil {
+			return 0, fmt.Errorf("LINK_DEVICE count devices: %w", err)
+		}
+		if active >= MaxDevicesPerOwner {
+			return 0, fmt.Errorf("%w: LINK_DEVICE: owner already has %d devices (max %d)",
+				ErrTxFailed, active, MaxDevicesPerOwner)
+		}
+		rec := DeviceRecord{
+			Owner:        tx.From,
+			X25519PubKey: p.X25519PubKey,
+			DeviceName:   p.DeviceName,
+			AddedAt:      tx.Timestamp.Unix(),
+		}
+		val, _ := json.Marshal(rec)
+		if err := txn.Set(devKey, val); err != nil {
+			return 0, err
+		}
+		idxKey := []byte(prefixDevicesByOwner + tx.From + ":" + p.X25519PubKey)
+		if err := txn.Set(idxKey, []byte{}); err != nil {
+			return 0, err
+		}
+
+	case EventUnlinkDevice:
+		// Revoke (soft-delete) a device record. Mark RevokedAt and keep
+		// the row — clients wake up, notice their own pub is revoked, and
+		// wipe local state. A permanent delete would let a sender that
+		// missed the revoke keep encrypting for the old pub silently.
+		if err := c.debitBalance(txn, tx.From, tx.Fee); err != nil {
+			return 0, fmt.Errorf("UNLINK_DEVICE debit: %w", err)
+		}
+		var p UnlinkDevicePayload
+		if err := json.Unmarshal(tx.Payload, &p); err != nil {
+			return 0, fmt.Errorf("%w: UNLINK_DEVICE bad payload: %v", ErrTxFailed, err)
+		}
+		if err := validateDevicePubKey(p.X25519PubKey); err != nil {
+			return 0, fmt.Errorf("%w: UNLINK_DEVICE: %v", ErrTxFailed, err)
+		}
+		devKey := []byte(prefixDevice + p.X25519PubKey)
+		item, err := txn.Get(devKey)
+		if err != nil {
+			return 0, fmt.Errorf("%w: UNLINK_DEVICE: device not found", ErrTxFailed)
+		}
+		var existing DeviceRecord
+		if verr := item.Value(func(v []byte) error {
+			return json.Unmarshal(v, &existing)
+		}); verr != nil {
+			return 0, fmt.Errorf("UNLINK_DEVICE decode: %w", verr)
+		}
+		if existing.Owner != tx.From {
+			return 0, fmt.Errorf("%w: UNLINK_DEVICE: signer is not the owner of this device",
+				ErrTxFailed)
+		}
+		if existing.RevokedAt != 0 {
+			// Already revoked — idempotent success, don't error.
+			break
+		}
+		existing.RevokedAt = tx.Timestamp.Unix()
+		updated, _ := json.Marshal(existing)
+		if err := txn.Set(devKey, updated); err != nil {
+			return 0, err
+		}
+		// Drop reverse index so countActiveDevicesForOwner is O(k_active).
+		idxKey := []byte(prefixDevicesByOwner + tx.From + ":" + p.X25519PubKey)
+		if err := txn.Delete(idxKey); err != nil {
+			return 0, err
+		}
+
 	case EventContactRequest:
 		var p ContactRequestPayload
 		if err := json.Unmarshal(tx.Payload, &p); err != nil {

blockchain/devices_test.go

@@ -0,0 +1,413 @@
+package blockchain_test
+
+// Multi-device registry tests (v2.2.0). Cover happy-path link + list,
+// unlink idempotency, ownership validation, max-devices guard, and
+// backward-compat sender fall-back semantics (empty list for unknown
+// master). HTTP-layer tests live in the node package; these stay at
+// chain level — applyTx + state-shape only.
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"go-blockchain/blockchain"
+	"go-blockchain/identity"
+)
+
+// uniqueTxID sidesteps the `chain_test.go:txID` race where two helper
+// calls in the same nanosecond produce identical tx IDs → chain.AddBlock
+// dedupes the second as "already committed". We add a strictly-monotonic
+// counter so every tx built in the same test gets a fresh ID even on
+// fast machines.
+var devicesTxIDCounter atomic.Uint64
+
+func uniqueTxID() string {
+	n := devicesTxIDCounter.Add(1)
+	h := make([]byte, 16)
+	_, _ = rand.Read(h)
+	return hex.EncodeToString(h) + ":" + time.Now().Format("150405.000000000") + ":" + itoa(n)
+}
+
+func itoa(n uint64) string {
+	// tiny local conversion to avoid importing strconv just for tests.
+	if n == 0 {
+		return "0"
+	}
+	var buf [20]byte
+	i := len(buf)
+	for n > 0 {
+		i--
+		buf[i] = byte('0' + n%10)
+		n /= 10
+	}
+	return string(buf[i:])
+}
+
+// linkDeviceRawTx / unlinkDeviceRawTx build txs with guaranteed-unique
+// IDs so we can stuff many of them into a single block during tests.
+func linkDeviceRawTx(master *identity.Identity, x25519Pub, name string) *blockchain.Transaction {
+	payload := mustJSON(blockchain.LinkDevicePayload{
+		X25519PubKey: x25519Pub,
+		DeviceName:   name,
+	})
+	return &blockchain.Transaction{
+		ID:        uniqueTxID(),
+		Type:      blockchain.EventLinkDevice,
+		From:      master.PubKeyHex(),
+		Fee:       blockchain.MinFee,
+		Payload:   payload,
+		Timestamp: time.Now().UTC(),
+	}
+}
+
+func unlinkDeviceRawTx(master *identity.Identity, x25519Pub string) *blockchain.Transaction {
+	payload := mustJSON(blockchain.UnlinkDevicePayload{X25519PubKey: x25519Pub})
+	return &blockchain.Transaction{
+		ID:        uniqueTxID(),
+		Type:      blockchain.EventUnlinkDevice,
+		From:      master.PubKeyHex(),
+		Fee:       blockchain.MinFee,
+		Payload:   payload,
+		Timestamp: time.Now().UTC(),
+	}
+}
+
+// randX25519Pub returns a throw-away 32-byte hex string suitable for the
+// x25519_pub_key field. We don't need the matching private key — the
+// chain only stores the pub and doesn't verify it's a valid curve point.
+func randX25519Pub(t *testing.T) string {
+	t.Helper()
+	var b [32]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		t.Fatalf("rand: %v", err)
+	}
+	return hex.EncodeToString(b[:])
+}
+
+// fundIdentity credits enough balance to cover `nFees` worth of MinFee
+// payments. Every test needs this because LINK_DEVICE and UNLINK_DEVICE
+// debit tx.Fee from the master's balance — without funding the first tx
+// errors with "insufficient funds" and no state changes.
+func fundIdentity(t *testing.T, c *blockchain.Chain, val, recipient *identity.Identity, nFees int) {
+	t.Helper()
+	amount := uint64(nFees+2) * blockchain.MinFee
+	tx := makeTx(blockchain.EventTransfer, val.PubKeyHex(), recipient.PubKeyHex(),
+		amount, blockchain.MinFee, mustJSON(blockchain.TransferPayload{}))
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{tx}))
+}
+
+// TestLinkDeviceHappyPath: after a single LINK_DEVICE, DevicesOf returns
+// exactly one record with the right owner/name/pub.
+func TestLinkDeviceHappyPath(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 1)
+	dev1 := randX25519Pub(t)
+	tx := linkDeviceRawTx(alice, dev1, "Alice's iPhone")
+	b := buildBlock(t, c.Tip(), val, []*blockchain.Transaction{tx})
+	mustAddBlock(t, c, b)
+
+	devs, err := c.DevicesOf(alice.PubKeyHex())
+	if err != nil {
+		t.Fatalf("DevicesOf: %v", err)
+	}
+	if len(devs) != 1 {
+		t.Fatalf("expected 1 device, got %d", len(devs))
+	}
+	got := devs[0]
+	if got.Owner != alice.PubKeyHex() {
+		t.Errorf("owner: got %s, want %s", got.Owner, alice.PubKeyHex())
+	}
+	if got.X25519PubKey != dev1 {
+		t.Errorf("x25519: got %s, want %s", got.X25519PubKey, dev1)
+	}
+	if got.DeviceName != "Alice's iPhone" {
+		t.Errorf("name: got %q, want %q", got.DeviceName, "Alice's iPhone")
+	}
+	if got.RevokedAt != 0 {
+		t.Errorf("freshly linked device should have RevokedAt=0, got %d", got.RevokedAt)
+	}
+}
+
+// TestLinkDeviceMultiple: multiple devices for the same owner all show up
+// in DevicesOf, and the count matches.
+func TestLinkDeviceMultiple(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 3)
+	pubs := []string{randX25519Pub(t), randX25519Pub(t), randX25519Pub(t)}
+	var txs []*blockchain.Transaction
+	for i, p := range pubs {
+		txs = append(txs, linkDeviceRawTx(alice, p, "device-"+string(rune('A'+i))))
+	}
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val, txs))
+
+	devs, err := c.DevicesOf(alice.PubKeyHex())
+	if err != nil {
+		t.Fatalf("DevicesOf: %v", err)
+	}
+	if len(devs) != 3 {
+		t.Fatalf("expected 3 devices, got %d", len(devs))
+	}
+}
+
+// TestLinkDeviceRejectsForeignOwner: if Alice already linked a X25519 pub
+// and Bob tries to link the SAME pub to himself, the tx is rejected.
+// This protects against a malicious actor hijacking someone else's
+// device-pub and trying to claim it.
+func TestLinkDeviceRejectsForeignOwner(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	bob := newIdentity(t)
+	fundIdentity(t, c, val, alice, 1)
+	fundIdentity(t, c, val, bob, 1)
+	dev := randX25519Pub(t)
+
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, dev, "alice phone")}))
+
+	// Bob tries to claim the same pub. The chain silently drops invalid
+	// txs (they're non-fatal for block commit), so we verify the *state*:
+	// Alice still owns the pub, Bob has zero devices.
+	bobTx := linkDeviceRawTx(bob, dev, "bob phone")
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{bobTx}))
+
+	aliceDevs, _ := c.DevicesOf(alice.PubKeyHex())
+	if len(aliceDevs) != 1 || aliceDevs[0].DeviceName != "alice phone" {
+		t.Fatalf("Alice should still own the device, got %+v", aliceDevs)
+	}
+	bobDevs, _ := c.DevicesOf(bob.PubKeyHex())
+	if len(bobDevs) != 0 {
+		t.Fatalf("Bob's hijack should have been rejected, got %+v", bobDevs)
+	}
+}
+
+// TestLinkDeviceSameOwnerRefresh: the same owner re-linking the same
+// x25519_pub is a rename/refresh (not an error), and the revoked flag
+// gets cleared if it was set.
+func TestLinkDeviceSameOwnerRefresh(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 3)
+	dev := randX25519Pub(t)
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, dev, "old name")}))
+
+	// Unlink then re-link — should restore the record.
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(alice, dev)}))
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, dev, "new name")}))
+
+	devs, err := c.DevicesOf(alice.PubKeyHex())
+	if err != nil {
+		t.Fatalf("DevicesOf: %v", err)
+	}
+	if len(devs) != 1 {
+		t.Fatalf("expected 1 active device after re-link, got %d", len(devs))
+	}
+	if devs[0].DeviceName != "new name" {
+		t.Errorf("expected refreshed name 'new name', got %q", devs[0].DeviceName)
+	}
+}
+
+// TestUnlinkDeviceRemovesFromActive: after UNLINK_DEVICE, DevicesOf no
+// longer returns that record — senders stop fanning out to it.
+func TestUnlinkDeviceRemovesFromActive(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 3)
+	keep := randX25519Pub(t)
+	revoke := randX25519Pub(t)
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{
+		linkDeviceRawTx(alice, keep, "kept"),
+		linkDeviceRawTx(alice, revoke, "revoked"),
+	}))
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(alice, revoke)}))
+
+	devs, err := c.DevicesOf(alice.PubKeyHex())
+	if err != nil {
+		t.Fatalf("DevicesOf: %v", err)
+	}
+	if len(devs) != 1 || devs[0].X25519PubKey != keep {
+		t.Fatalf("expected only the kept device, got %+v", devs)
+	}
+}
+
+// TestUnlinkDeviceRejectsForeignSigner: Bob can't unlink Alice's device
+// even if he knows the X25519 pub — only the owner's signature (= tx.From)
+// authorises revoke.
+func TestUnlinkDeviceRejectsForeignSigner(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	bob := newIdentity(t)
+	fundIdentity(t, c, val, alice, 1)
+	fundIdentity(t, c, val, bob, 1)
+	dev := randX25519Pub(t)
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, dev, "alice phone")}))
+
+	// Bob tries to unlink Alice's device — tx is silently dropped, Alice
+	// still has it in her active list.
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(bob, dev)}))
+
+	aliceDevs, _ := c.DevicesOf(alice.PubKeyHex())
+	if len(aliceDevs) != 1 || aliceDevs[0].X25519PubKey != dev {
+		t.Fatalf("Alice's device should still be active, got %+v", aliceDevs)
+	}
+}
+
+// TestUnlinkDeviceIdempotent: unlinking a device that's already revoked
+// does NOT error — this is needed for recovery scenarios where a client
+// retries the tx after a spotty connection.
+func TestUnlinkDeviceIdempotent(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 3)
+	dev := randX25519Pub(t)
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, dev, "phone")}))
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(alice, dev)}))
+	// Second unlink of the same device must apply cleanly.
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(alice, dev)}))
+}
+
+// TestLinkDeviceRejectsMalformedPub: payload.X25519PubKey must be 64-char
+// lowercase hex. Garbage / short / uppercase values are rejected at
+// applyTx time before any state change.
+func TestLinkDeviceRejectsMalformedPub(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 5)
+
+	bad := []string{
+		"",                      // empty
+		"abc",                   // too short
+		strings.Repeat("x", 64), // non-hex
+		strings.Repeat("A", 64), // uppercase
+	}
+	for _, p := range bad {
+		tx := linkDeviceRawTx(alice, p, "dev")
+		mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{tx}))
+	}
+
+	devs, _ := c.DevicesOf(alice.PubKeyHex())
+	if len(devs) != 0 {
+		t.Fatalf("expected 0 devices after %d malformed link attempts, got %d",
+			len(bad), len(devs))
+	}
+}
+
+// TestLinkDeviceRejectsBadDeviceName: empty, too long, or control-char
+// names are refused — this field is rendered verbatim in clients.
+func TestLinkDeviceRejectsBadDeviceName(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	fundIdentity(t, c, val, alice, 5)
+	cases := map[string]string{
+		"empty":        "",
+		"too long":     strings.Repeat("a", blockchain.MaxDeviceNameLen+1),
+		"control char": "device\x01name",
+	}
+	for name, devName := range cases {
+		t.Run(name, func(t *testing.T) {
+			before, _ := c.DevicesOf(alice.PubKeyHex())
+			tx := linkDeviceRawTx(alice, randX25519Pub(t), devName)
+			mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{tx}))
+			after, _ := c.DevicesOf(alice.PubKeyHex())
+			if len(after) != len(before) {
+				t.Fatalf("bad %s name should not have been linked (before=%d, after=%d)",
+					name, len(before), len(after))
+			}
+		})
+	}
+}
+
+// TestLinkDeviceMaxDevices: after MaxDevicesPerOwner active devices, any
+// further LINK_DEVICE is rejected. Revoking one frees a slot.
+func TestLinkDeviceMaxDevices(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	// Enough for cap + one overflow attempt + one unlink + one replacement.
+	fundIdentity(t, c, val, alice, blockchain.MaxDevicesPerOwner+4)
+
+	// Fill to the cap — each in its own block so timestamps differ.
+	pubs := make([]string, blockchain.MaxDevicesPerOwner)
+	for i := 0; i < blockchain.MaxDevicesPerOwner; i++ {
+		pubs[i] = randX25519Pub(t)
+		mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+			[]*blockchain.Transaction{linkDeviceRawTx(alice, pubs[i], "d")}))
+	}
+	// One more — the tx is dropped, cap stays exact.
+	over := linkDeviceRawTx(alice, randX25519Pub(t), "overflow")
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val, []*blockchain.Transaction{over}))
+	if devs, _ := c.DevicesOf(alice.PubKeyHex()); len(devs) != blockchain.MaxDevicesPerOwner {
+		t.Fatalf("overflow link should have been rejected, count=%d", len(devs))
+	}
+
+	// Revoke one, then a fresh link succeeds.
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{unlinkDeviceRawTx(alice, pubs[0])}))
+	mustAddBlock(t, c, buildBlock(t, c.Tip(), val,
+		[]*blockchain.Transaction{linkDeviceRawTx(alice, randX25519Pub(t), "replacement")}))
+	if devs, _ := c.DevicesOf(alice.PubKeyHex()); len(devs) != blockchain.MaxDevicesPerOwner {
+		t.Fatalf("after unlink+relink, should be %d active, got %d",
+			blockchain.MaxDevicesPerOwner, len(devs))
+	}
+}
+
+// TestDevicesOfEmptyForUnknown: unknown master pubs return an empty list
+// (not an error) — this preserves the sender's ability to fall back to
+// IdentityInfo.X25519Pub for legacy identities.
+func TestDevicesOfEmptyForUnknown(t *testing.T) {
+	c := newChain(t)
+	val := newIdentity(t)
+	addGenesis(t, c, val)
+
+	alice := newIdentity(t)
+	devs, err := c.DevicesOf(alice.PubKeyHex())
+	if err != nil {
+		t.Fatalf("DevicesOf: %v", err)
+	}
+	if len(devs) != 0 {
+		t.Fatalf("expected 0 devices for unknown master, got %d", len(devs))
+	}
+}

blockchain/types.go

@@ -46,6 +46,14 @@ const (
 	EventUnfollow        EventType = "UNFOLLOW"          // unfollow an author
 	EventLikePost        EventType = "LIKE_POST"         // like a post
 	EventUnlikePost      EventType = "UNLIKE_POST"       // remove a previous like
+
+	// Multi-device support (v2.2.0): each physical device of an identity gets
+	// its own X25519 keypair for the messenger mailbox. LINK/UNLINK_DEVICE
+	// publish/revoke those pubs on-chain so senders can fan-out envelopes
+	// across the recipient's active devices. Signed by the identity's
+	// master Ed25519 key.
+	EventLinkDevice   EventType = "LINK_DEVICE"
+	EventUnlinkDevice EventType = "UNLINK_DEVICE"
 )
 
 // Token amounts are stored in micro-tokens (µT).
@@ -554,7 +562,71 @@ type IdentityInfo struct {
 	Address    string `json:"address"`
 	X25519Pub  string `json:"x25519_pub"`  // hex Curve25519 key; empty if not published
 	Nickname   string `json:"nickname"`
-	Registered bool   `json:"registered"`  // true if REGISTER_KEY tx was committed
+	Registered bool   `json:"registered"`   // true if REGISTER_KEY tx was committed
+	// DeviceCount is the number of currently-linked (non-revoked) devices in
+	// this identity's multi-device registry. `0` for legacy identities that
+	// only published a single X25519 via REGISTER_KEY — senders fall back
+	// to IdentityInfo.X25519Pub in that case.
+	DeviceCount int `json:"device_count"`
+}
+
+// ── Multi-device registry (v2.2.0) ───────────────────────────────────────
+
+// MaxDevicesPerOwner caps how many devices a single identity can have
+// linked concurrently. A sender must encrypt + relay one envelope per
+// device, so the multiplier bounds the per-message cost. Ten covers
+// typical users (phone + tablet + laptop + desktop + work phone + …)
+// without letting an abuse case blow up mailbox traffic. Revoked devices
+// don't count.
+const MaxDevicesPerOwner = 10
+
+// MaxDeviceNameLen caps the length of a human-friendly device label
+// ("Alice's iPhone 14", "Work MacBook Pro"). Longer names get rejected
+// at validation. Kept short to discourage using this field as a free-form
+// comment/profile channel.
+const MaxDeviceNameLen = 64
+
+// LinkDevicePayload is embedded in EventLinkDevice transactions. Master
+// Ed25519 (= tx.From) asserts that the given X25519 pub belongs to one
+// of its physical devices, publishing it so senders can fan out envelopes.
+type LinkDevicePayload struct {
+	// X25519PubKey is the hex-encoded Curve25519 pub the device generated
+	// locally. Must be unique in the device registry — senders index
+	// envelopes by this key in the relay mailbox.
+	X25519PubKey string `json:"x25519_pub_key"`
+	// DeviceName is a short human label shown in Settings → Devices.
+	// Purely informational; not used for routing.
+	DeviceName string `json:"device_name"`
+}
+
+// UnlinkDevicePayload is embedded in EventUnlinkDevice transactions. Signed
+// by master Ed25519; marks the referenced device as revoked so senders
+// stop shipping envelopes to its X25519 pub. The revoked device itself,
+// once it sees its pub in the revoked list, is expected to wipe its
+// local state (master Ed25519 priv + chat cache).
+type UnlinkDevicePayload struct {
+	X25519PubKey string `json:"x25519_pub_key"`
+}
+
+// DeviceRecord is the on-chain persisted state for one device link.
+// Stored at key `prefixDevice + x25519_pub`; the reverse index
+// `prefixDevicesByOwner + master_pub` keeps a slice of x25519 pubs per
+// owner for efficient listing.
+type DeviceRecord struct {
+	Owner        string `json:"owner"`          // master Ed25519 pub hex
+	X25519PubKey string `json:"x25519_pub_key"` // device X25519 pub hex
+	DeviceName   string `json:"device_name"`
+	AddedAt      int64  `json:"added_at"`           // unix seconds, from tx timestamp
+	RevokedAt    int64  `json:"revoked_at,omitempty"` // 0 = active; >0 = revoked
+}
+
+// DeviceInfo is the public view of a DeviceRecord served by
+// GET /api/devices/{master_pub}. Revoked records are not included
+// in the response (intentionally — sender only needs the active set).
+type DeviceInfo struct {
+	X25519PubKey string `json:"x25519_pub_key"`
+	DeviceName   string `json:"device_name"`
+	AddedAt      int64  `json:"added_at"`
 }
 
 // ConsensusMessage types used by the PBFT engine over the P2P layer.

client-app/app.json

@@ -12,12 +12,14 @@
       "infoPlist": {
         "NSMicrophoneUsageDescription": "Allow DChain to record voice messages and video.",
         "NSCameraUsageDescription": "Allow DChain to record video messages and scan QR codes.",
-        "NSPhotoLibraryUsageDescription": "Allow DChain to attach photos and videos from your library."
+        "NSPhotoLibraryUsageDescription": "Allow DChain to attach photos and videos from your library.",
+        "ITSAppUsesNonExemptEncryption": false
       }
     },
     "android": {
       "package": "com.dchain.messenger",
       "softwareKeyboardLayoutMode": "pan",
+      "usesCleartextTraffic": true,
       "permissions": [
         "android.permission.RECORD_AUDIO",
         "android.permission.CAMERA",

client-app/app/(app)/_layout.tsx

@@ -13,7 +13,7 @@
  * один раз; переходы между tab'ами их не перезапускают.
  */
 import React, { useEffect } from 'react';
-import { View } from 'react-native';
+import { View, Platform } from 'react-native';
 import { router, usePathname } from 'expo-router';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
 import { useStore } from '@/lib/store';
@@ -25,7 +25,13 @@ import { useGlobalInbox } from '@/hooks/useGlobalInbox';
 import { getWSClient } from '@/lib/ws';
 import { NavBar } from '@/components/NavBar';
 import { AnimatedSlot } from '@/components/AnimatedSlot';
-import { saveContact } from '@/lib/storage';
+import {
+  saveContact,
+  isDeviceRegistered, markDeviceRegistered, wipeAllLocalState,
+} from '@/lib/storage';
+import {
+  fetchDevices, buildLinkDeviceTx, submitTx,
+} from '@/lib/api';
 
 export default function AppLayout() {
   const keyFile  = useStore(s => s.keyFile);
@@ -73,6 +79,79 @@ export default function AppLayout() {
     else ws.setAuthCreds(null);
   }, [keyFile]);
 
+  // Multi-device registry bootstrap + revoke-detection (v2.2.0).
+  //
+  // Three branches, by (chain list × local "was registered" flag):
+  //
+  //   1. Our pub is in the chain's active list →
+  //      mark us registered locally (idempotent), done.
+  //
+  //   2. Our pub is NOT in the active list, AND we've registered before →
+  //      another device issued UNLINK_DEVICE against us. Wipe ALL local
+  //      state (master priv, contacts, chats, marker) and redirect to
+  //      the auth screen. This is the security-critical path: without
+  //      the wipe, a stolen phone after revoke would still decrypt
+  //      historical messages.
+  //
+  //   3. Our pub is NOT in the active list, AND we've NEVER registered →
+  //      first boot on this chain; submit LINK_DEVICE so senders can
+  //      target us. Failures (fee, offline) are swallowed; next launch
+  //      retries.
+  useEffect(() => {
+    if (!keyFile) return;
+    let cancelled = false;
+    (async () => {
+      let chainList;
+      try {
+        chainList = await fetchDevices(keyFile.pub_key);
+      } catch {
+        // Network unavailable — leave state unchanged; we'll resync on
+        // the next launch. Do NOT wipe on network error.
+        return;
+      }
+      if (cancelled) return;
+
+      const inActive = chainList.some(d => d.x25519_pub_key === keyFile.x25519_pub);
+      const previouslyRegistered = await isDeviceRegistered();
+      if (cancelled) return;
+
+      if (inActive) {
+        // Branch #1 — ensure the local marker is set.
+        if (!previouslyRegistered) await markDeviceRegistered();
+        return;
+      }
+
+      if (previouslyRegistered) {
+        // Branch #2 — REVOKED. Self-wipe.
+        await wipeAllLocalState();
+        useStore.getState().setKeyFile(null);
+        // The redirect-on-null-keyFile effect below will push the user
+        // back to the welcome screen automatically.
+        return;
+      }
+
+      // Branch #3 — first-boot link. Best-effort.
+      try {
+        const deviceName = Platform.select({
+          ios:     'iPhone',
+          android: 'Android phone',
+          default: 'Device',
+        }) ?? 'Device';
+        const tx = buildLinkDeviceTx({
+          from:       keyFile.pub_key,
+          x25519Pub:  keyFile.x25519_pub,
+          deviceName,
+          privKey:    keyFile.priv_key,
+        });
+        await submitTx(tx);
+        await markDeviceRegistered();
+      } catch {
+        /* next launch retries */
+      }
+    })();
+    return () => { cancelled = true; };
+  }, [keyFile]);
+
   useEffect(() => {
     if (keyFile === null) {
       const t = setTimeout(() => {

client-app/app/(app)/chats/[id].tsx

@@ -23,7 +23,7 @@ import * as Clipboard from 'expo-clipboard';
 import { useStore } from '@/lib/store';
 import { useMessages } from '@/hooks/useMessages';
 import { encryptMessage } from '@/lib/crypto';
-import { sendEnvelope } from '@/lib/api';
+import { sendEnvelope, resolveRecipientKeys } from '@/lib/api';
 import { getWSClient } from '@/lib/ws';
 import { appendMessage, loadMessages } from '@/lib/storage';
 import { randomId, safeBack } from '@/lib/utils';
@@ -212,15 +212,34 @@ export default function ChatScreen() {
       // leaves the device, so no encryption/fee/network round-trip is needed.
       // Regular chats still go through the NaCl + relay pipeline below.
       if (hasText && !isSavedMessages) {
-        const { nonce, ciphertext } = encryptMessage(
+        // Multi-device fan-out (v2.2.0): resolve the recipient's active
-          actualText.trim(), keyFile.x25519_priv, contact.x25519Pub,
+        // device X25519 pubs via /api/devices. Legacy identities (no
-        );
+        // devices registered) fall back to their published identity
-        await sendEnvelope({
+        // x25519 pub, preserving the pre-v2.2.0 single-device path.
-          senderPub:    keyFile.x25519_pub,
+        // `contact.x25519Pub` stays the floor — if both network calls
-          recipientPub: contact.x25519Pub,
+        // fail we still attempt delivery to the cached pub so a flaky
-          senderEd25519Pub: keyFile.pub_key,
+        // connection doesn't block outgoing messages.
-          nonce, ciphertext,
+        let recipientPubs = await resolveRecipientKeys(contact.address);
-        });
+        if (recipientPubs.length === 0 && contact.x25519Pub) {
+          recipientPubs = [contact.x25519Pub];
+        }
+        if (recipientPubs.length === 0) {
+          throw new Error('recipient has no encryption key published');
+        }
+        // One sealed envelope per recipient device. Parallel — slow
+        // relays don't block each other; any individual failure
+        // rejects the whole send (user retries).
+        await Promise.all(recipientPubs.map(async (rpub) => {
+          const { nonce, ciphertext } = encryptMessage(
+            actualText.trim(), keyFile.x25519_priv, rpub,
+          );
+          await sendEnvelope({
+            senderPub:    keyFile.x25519_pub,
+            recipientPub: rpub,
+            senderEd25519Pub: keyFile.pub_key,
+            nonce, ciphertext,
+          });
+        }));
       }
 
       const msg: Message = {

client-app/app/(app)/devices.tsx

@@ -0,0 +1,490 @@
+/**
+ * Devices screen — Settings → Linked devices.
+ *
+ * Multi-device registry (v2.2.0). Lists every X25519 device published
+ * on-chain under this identity's master Ed25519 key. Operators can:
+ *   - see added-at timestamps
+ *   - rename this device (local alias for now; rename via LINK_DEVICE
+ *     with same pub + new name is a v2.3 polish)
+ *   - revoke a remote device via UNLINK_DEVICE (requires fee)
+ *   - pair a new device (Phase 3 — separate modal, stub for now)
+ *
+ * This device is NEVER listed with an Unlink button — revoking yourself
+ * is a footgun (you'd wipe your own state on next launch). Export/import
+ * your key first, then revoke from the new device.
+ */
+import React, { useCallback, useEffect, useState } from 'react';
+import {
+  View, Text, ScrollView, Pressable, ActivityIndicator, Alert, RefreshControl,
+  TextInput, KeyboardAvoidingView, Platform, Modal,
+} from 'react-native';
+import { Ionicons } from '@expo/vector-icons';
+import { useSafeAreaInsets } from 'react-native-safe-area-context';
+
+import { useStore } from '@/lib/store';
+import {
+  fetchDevices, buildLinkDeviceTx, buildUnlinkDeviceTx, submitTx,
+  sendEnvelope, humanizeTxError,
+  type DeviceInfo,
+} from '@/lib/api';
+import { encryptMessage } from '@/lib/crypto';
+import { Header } from '@/components/Header';
+import { IconButton } from '@/components/IconButton';
+import { safeBack } from '@/lib/utils';
+
+function shortPub(p: string, n = 8): string {
+  if (!p) return '—';
+  return p.length <= n * 2 + 1 ? p : `${p.slice(0, n)}…${p.slice(-n)}`;
+}
+
+function formatDate(unixSec: number): string {
+  return new Date(unixSec * 1000).toLocaleString();
+}
+
+export default function DevicesScreen() {
+  const insets  = useSafeAreaInsets();
+  const keyFile = useStore(s => s.keyFile);
+
+  const [devices, setDevices]       = useState<DeviceInfo[]>([]);
+  const [loading, setLoading]       = useState(true);
+  const [refreshing, setRefreshing] = useState(false);
+  const [unlinking, setUnlinking]   = useState<string | null>(null); // pub being revoked
+
+  const load = useCallback(async (isRefresh = false) => {
+    if (!keyFile) return;
+    if (isRefresh) setRefreshing(true);
+    else setLoading(true);
+    try {
+      const list = await fetchDevices(keyFile.pub_key);
+      setDevices(list);
+    } finally {
+      setLoading(false);
+      setRefreshing(false);
+    }
+  }, [keyFile]);
+
+  useEffect(() => { load(false); }, [load]);
+
+  const onUnlink = useCallback((dev: DeviceInfo) => {
+    if (!keyFile) return;
+    Alert.alert(
+      'Unlink device?',
+      `"${dev.device_name}" will stop receiving messages sent to you. ` +
+      `This costs a small network fee. The revoked device wipes its ` +
+      `local state the next time it checks in.`,
+      [
+        { text: 'Cancel', style: 'cancel' },
+        {
+          text: 'Unlink',
+          style: 'destructive',
+          onPress: async () => {
+            setUnlinking(dev.x25519_pub_key);
+            try {
+              const tx = buildUnlinkDeviceTx({
+                from:      keyFile.pub_key,
+                x25519Pub: dev.x25519_pub_key,
+                privKey:   keyFile.priv_key,
+              });
+              await submitTx(tx);
+              // Optimistic — drop from local list immediately; next load
+              // reconciles. Chain tx takes ~1 block to commit.
+              setDevices(prev => prev.filter(d => d.x25519_pub_key !== dev.x25519_pub_key));
+            } catch (e: any) {
+              Alert.alert('Unlink failed', humanizeTxError(e));
+            } finally {
+              setUnlinking(null);
+            }
+          },
+        },
+      ],
+    );
+  }, [keyFile]);
+
+  const meX25519 = keyFile?.x25519_pub ?? '';
+
+  // Pairing modal state — filled by the operator reading values off the
+  // new device's /auth/pair screen.
+  const [pairOpen, setPairOpen]             = useState(false);
+  const [pairCode, setPairCode]             = useState('');
+  const [pairKey,  setPairKey]              = useState('');
+  const [pairName, setPairName]             = useState('');
+  const [pairBusy, setPairBusy]             = useState(false);
+
+  const submitPair = useCallback(async () => {
+    if (!keyFile) return;
+    const code = pairCode.replace(/\s+/g, '').trim();
+    const key  = pairKey.replace(/\s+/g, '').trim().toLowerCase();
+    if (!/^\d{6}$/.test(code)) {
+      Alert.alert('Invalid code', 'The pairing code is 6 digits.');
+      return;
+    }
+    if (!/^[0-9a-f]{64}$/.test(key)) {
+      Alert.alert('Invalid key', 'The device key must be 64 hex characters.');
+      return;
+    }
+    const name = pairName.trim() || 'New device';
+    setPairBusy(true);
+    try {
+      // 1. LINK_DEVICE on-chain so senders learn the new pub.
+      const tx = buildLinkDeviceTx({
+        from:       keyFile.pub_key,
+        x25519Pub:  key,
+        deviceName: name,
+        privKey:    keyFile.priv_key,
+      });
+      await submitTx(tx);
+      // 2. Ship the handshake payload to the new device. Encrypted for
+      //    its x25519 pub so only it can read — master priv in plaintext
+      //    would be catastrophic, E2E is the whole point.
+      const payload = JSON.stringify({
+        v: 1,
+        type: 'pair-handshake',
+        code,
+        master_pub:        keyFile.pub_key,
+        master_priv:       keyFile.priv_key,
+        master_x25519_pub: keyFile.x25519_pub,
+      });
+      const { nonce, ciphertext } = encryptMessage(
+        payload, keyFile.x25519_priv, key,
+      );
+      await sendEnvelope({
+        senderPub:    keyFile.x25519_pub,
+        recipientPub: key,
+        senderEd25519Pub: keyFile.pub_key,
+        nonce, ciphertext,
+      });
+      // 3. Optimistic local insert so the row shows up without waiting
+      //    for the next pull/refresh round-trip.
+      setDevices(prev => {
+        if (prev.some(d => d.x25519_pub_key === key)) return prev;
+        return [...prev, {
+          x25519_pub_key: key,
+          device_name:    name,
+          added_at:       Math.floor(Date.now() / 1000),
+        }];
+      });
+      setPairOpen(false);
+      setPairCode(''); setPairKey(''); setPairName('');
+      Alert.alert(
+        'Pairing sent',
+        'The new device should finish pairing in a few seconds.',
+      );
+    } catch (e: any) {
+      Alert.alert('Pairing failed', humanizeTxError(e));
+    } finally {
+      setPairBusy(false);
+    }
+  }, [keyFile, pairCode, pairKey, pairName]);
+
+  return (
+    <View style={{ flex: 1, backgroundColor: '#000000', paddingTop: insets.top }}>
+      <Header
+        title="Devices"
+        divider
+        left={<IconButton icon="chevron-back" size={36} onPress={() => safeBack()} />}
+      />
+
+      <ScrollView
+        contentContainerStyle={{ padding: 14, paddingBottom: insets.bottom + 30 }}
+        refreshControl={
+          <RefreshControl
+            refreshing={refreshing}
+            onRefresh={() => load(true)}
+            tintColor="#1d9bf0"
+          />
+        }
+      >
+        <Text style={{ color: '#8b8b8b', fontSize: 12, lineHeight: 17, marginBottom: 14 }}>
+          Every linked device has its own encryption key. Messages sent to you
+          are delivered to all active devices.
+        </Text>
+
+        {loading ? (
+          <View style={{ paddingTop: 60, alignItems: 'center' }}>
+            <ActivityIndicator color="#1d9bf0" />
+          </View>
+        ) : devices.length === 0 ? (
+          <View style={{
+            paddingTop: 60, alignItems: 'center', paddingHorizontal: 24,
+          }}>
+            <Ionicons name="phone-portrait-outline" size={36} color="#3a3a3a" />
+            <Text style={{
+              color: '#ffffff', fontSize: 15, fontWeight: '700',
+              marginTop: 10,
+            }}>
+              No devices registered yet
+            </Text>
+            <Text style={{
+              color: '#8b8b8b', fontSize: 13, textAlign: 'center',
+              marginTop: 6, lineHeight: 19,
+            }}>
+              This device auto-registers when the next network-fee is available.
+              Top up your balance and pull to refresh.
+            </Text>
+          </View>
+        ) : (
+          <View style={{
+            borderRadius: 14,
+            backgroundColor: '#0a0a0a',
+            borderWidth: 1, borderColor: '#1f1f1f',
+            overflow: 'hidden',
+          }}>
+            {devices.map((d, i) => {
+              const isMe = d.x25519_pub_key === meX25519;
+              const busy = unlinking === d.x25519_pub_key;
+              return (
+                <View key={d.x25519_pub_key}>
+                  {i > 0 && <View style={{ height: 1, backgroundColor: '#1f1f1f' }} />}
+                  <View style={{
+                    flexDirection: 'row', alignItems: 'center',
+                    paddingHorizontal: 14, paddingVertical: 14, gap: 12,
+                  }}>
+                    <Ionicons
+                      name={isMe ? 'phone-portrait' : 'phone-portrait-outline'}
+                      size={22}
+                      color={isMe ? '#1d9bf0' : '#d0d0d0'}
+                    />
+                    <View style={{ flex: 1, minWidth: 0 }}>
+                      <View style={{ flexDirection: 'row', alignItems: 'center', gap: 6 }}>
+                        <Text
+                          style={{ color: '#ffffff', fontSize: 15, fontWeight: '700' }}
+                          numberOfLines={1}
+                        >
+                          {d.device_name || 'Unnamed device'}
+                        </Text>
+                        {isMe && (
+                          <View style={{
+                            paddingHorizontal: 6, paddingVertical: 1,
+                            borderRadius: 6, backgroundColor: '#0d2540',
+                          }}>
+                            <Text style={{ color: '#1d9bf0', fontSize: 10, fontWeight: '700' }}>
+                              THIS DEVICE
+                            </Text>
+                          </View>
+                        )}
+                      </View>
+                      <Text
+                        style={{
+                          color: '#8b8b8b', fontSize: 11, fontFamily: 'monospace',
+                          marginTop: 3,
+                        }}
+                        numberOfLines={1}
+                      >
+                        {shortPub(d.x25519_pub_key)}
+                      </Text>
+                      <Text style={{ color: '#6a6a6a', fontSize: 11, marginTop: 2 }}>
+                        Linked {formatDate(d.added_at)}
+                      </Text>
+                    </View>
+                    {!isMe && (
+                      <Pressable
+                        onPress={() => onUnlink(d)}
+                        disabled={busy}
+                        style={({ pressed }) => ({
+                          paddingHorizontal: 12, paddingVertical: 7,
+                          borderRadius: 999,
+                          borderWidth: 1, borderColor: '#3a2020',
+                          backgroundColor: pressed ? '#2a1414' : 'transparent',
+                          opacity: busy ? 0.5 : 1,
+                        })}
+                      >
+                        {busy ? (
+                          <ActivityIndicator size="small" color="#ff6b6b" />
+                        ) : (
+                          <Text style={{ color: '#ff6b6b', fontSize: 12, fontWeight: '700' }}>
+                            Unlink
+                          </Text>
+                        )}
+                      </Pressable>
+                    )}
+                  </View>
+                </View>
+              );
+            })}
+          </View>
+        )}
+
+        {/* Link new device — opens a modal with Code + DeviceKey inputs
+            that the operator transcribes from the new device's
+            /auth/pair screen. */}
+        <View style={{ marginTop: 18 }}>
+          <Pressable
+            onPress={() => setPairOpen(true)}
+            style={({ pressed }) => ({
+              paddingVertical: 13, paddingHorizontal: 16,
+              borderRadius: 14,
+              backgroundColor: pressed ? '#1a1a1a' : '#0a0a0a',
+              borderWidth: 1, borderColor: '#1f1f1f',
+              flexDirection: 'row', alignItems: 'center', gap: 10,
+            })}
+          >
+            <Ionicons name="link-outline" size={18} color="#1d9bf0" />
+            <View style={{ flex: 1 }}>
+              <Text style={{ color: '#ffffff', fontSize: 14, fontWeight: '700' }}>
+                Link new device
+              </Text>
+              <Text style={{ color: '#8b8b8b', fontSize: 12, marginTop: 2 }}>
+                Enter the 6-digit code from the new device
+              </Text>
+            </View>
+            <Ionicons name="chevron-forward" size={18} color="#6a6a6a" />
+          </Pressable>
+        </View>
+      </ScrollView>
+
+      {/* ── Pair new device modal ───────────────────────────────────── */}
+      <Modal
+        visible={pairOpen}
+        animationType="fade"
+        transparent
+        onRequestClose={() => !pairBusy && setPairOpen(false)}
+      >
+        <KeyboardAvoidingView
+          behavior={Platform.OS === 'ios' ? 'padding' : undefined}
+          style={{
+            flex: 1,
+            backgroundColor: 'rgba(0,0,0,0.7)',
+            justifyContent: 'center', alignItems: 'center',
+            paddingHorizontal: 20,
+          }}
+        >
+          <View style={{
+            width: '100%', maxWidth: 420,
+            backgroundColor: '#0a0a0a',
+            borderRadius: 18,
+            borderWidth: 1, borderColor: '#1f1f1f',
+            padding: 20, gap: 12,
+          }}>
+            <View style={{
+              flexDirection: 'row', alignItems: 'center',
+              justifyContent: 'space-between', marginBottom: 4,
+            }}>
+              <Text style={{ color: '#ffffff', fontSize: 18, fontWeight: '800' }}>
+                Link new device
+              </Text>
+              <Pressable
+                onPress={() => !pairBusy && setPairOpen(false)}
+                hitSlop={8}
+              >
+                <Ionicons name="close" size={22} color="#8b8b8b" />
+              </Pressable>
+            </View>
+
+            <Text style={{ color: '#8b8b8b', fontSize: 12, lineHeight: 18 }}>
+              Open the new device, tap <Text style={{ color: '#ffffff' }}>Pair</Text> on
+              the welcome screen, then transcribe the code + device key shown there.
+            </Text>
+
+            <PairInput
+              label="6-digit code"
+              value={pairCode}
+              onChangeText={setPairCode}
+              placeholder="000000"
+              keyboardType="number-pad"
+              maxLength={6}
+              monospace
+            />
+            <PairInput
+              label="Device key"
+              value={pairKey}
+              onChangeText={setPairKey}
+              placeholder="64 hex chars"
+              autoCapitalize="none"
+              maxLength={64}
+              monospace
+            />
+            <PairInput
+              label="Name for this device (optional)"
+              value={pairName}
+              onChangeText={setPairName}
+              placeholder="e.g. Alice's laptop"
+              maxLength={64}
+            />
+
+            <View style={{
+              flexDirection: 'row', justifyContent: 'flex-end',
+              gap: 10, marginTop: 8,
+            }}>
+              <Pressable
+                onPress={() => setPairOpen(false)}
+                disabled={pairBusy}
+                style={({ pressed }) => ({
+                  paddingHorizontal: 16, paddingVertical: 10,
+                  borderRadius: 999,
+                  backgroundColor: pressed ? '#1a1a1a' : 'transparent',
+                  opacity: pairBusy ? 0.5 : 1,
+                })}
+              >
+                <Text style={{ color: '#8b8b8b', fontSize: 14, fontWeight: '700' }}>
+                  Cancel
+                </Text>
+              </Pressable>
+              <Pressable
+                onPress={submitPair}
+                disabled={pairBusy}
+                style={({ pressed }) => ({
+                  paddingHorizontal: 18, paddingVertical: 10,
+                  borderRadius: 999,
+                  backgroundColor: pressed ? '#1580c8' : '#1d9bf0',
+                  opacity: pairBusy ? 0.7 : 1,
+                  minWidth: 90, alignItems: 'center',
+                })}
+              >
+                {pairBusy ? (
+                  <ActivityIndicator size="small" color="#ffffff" />
+                ) : (
+                  <Text style={{ color: '#ffffff', fontSize: 14, fontWeight: '700' }}>
+                    Link
+                  </Text>
+                )}
+              </Pressable>
+            </View>
+          </View>
+        </KeyboardAvoidingView>
+      </Modal>
+    </View>
+  );
+}
+
+function PairInput({
+  label, value, onChangeText, placeholder, keyboardType, autoCapitalize,
+  maxLength, monospace,
+}: {
+  label: string;
+  value: string;
+  onChangeText: (v: string) => void;
+  placeholder?: string;
+  keyboardType?: 'default' | 'number-pad';
+  autoCapitalize?: 'none' | 'sentences';
+  maxLength?: number;
+  monospace?: boolean;
+}) {
+  return (
+    <View>
+      <Text style={{
+        color: '#8b8b8b', fontSize: 11, fontWeight: '700',
+        textTransform: 'uppercase', letterSpacing: 1, marginBottom: 6,
+      }}>
+        {label}
+      </Text>
+      <TextInput
+        value={value}
+        onChangeText={onChangeText}
+        placeholder={placeholder}
+        placeholderTextColor="#3a3a3a"
+        keyboardType={keyboardType}
+        autoCapitalize={autoCapitalize ?? 'sentences'}
+        autoCorrect={false}
+        maxLength={maxLength}
+        style={{
+          color: '#ffffff', fontSize: monospace ? 13 : 14,
+          fontFamily: monospace ? 'monospace' : undefined,
+          backgroundColor: '#000000',
+          borderRadius: 10,
+          paddingHorizontal: 12, paddingVertical: 10,
+          borderWidth: 1, borderColor: '#1f1f1f',
+        }}
+      />
+    </View>
+  );
+}

client-app/app/(app)/settings.tsx

@@ -492,6 +492,18 @@ export default function SettingsScreen() {
           />
         </Card>
 
+        {/* ── Devices — multi-device registry (v2.2.0) ── */}
+        <SectionLabel>Devices</SectionLabel>
+        <Card>
+          <Row
+            icon="phone-portrait-outline"
+            label="Linked devices"
+            value="Manage the devices that receive your messages"
+            onPress={() => router.push('/(app)/devices' as never)}
+            first
+          />
+        </Card>
+
         {/* ── Account ── */}
         <SectionLabel>Account</SectionLabel>
         <Card>

client-app/app/(auth)/pair.tsx

@@ -0,0 +1,300 @@
+/**
+ * Pair — secondary-device onboarding.
+ *
+ * Flow (new device, this screen):
+ *   1. Generate a fresh X25519 keypair locally + random 6-digit code.
+ *   2. Display { code, device x25519 pub }. User enters both on their
+ *      primary device (Settings → Devices → Link new device).
+ *   3. Primary device:
+ *        - submits LINK_DEVICE tx to publish our pub under its master,
+ *        - sends a relay envelope to our x25519 pub, encrypted with its
+ *          own x25519 priv, containing { code, master_pub, master_priv,
+ *          master_x25519_pub }.
+ *   4. We poll /relay/inbox every few seconds; when a decryptable
+ *      envelope arrives whose payload.code matches our displayed code,
+ *      we treat it as the handshake, assemble a KeyFile, save it, and
+ *      redirect into (app).
+ *
+ * Security notes:
+ *   - Master Ed25519 priv travels only via this envelope, encrypted for
+ *     this device's X25519 pub (which only this device holds the priv
+ *     for). Exposure is limited to one successful decrypt; we DELETE
+ *     the envelope from the mailbox immediately.
+ *   - The 6-digit code defends against a confused primary device paired
+ *     with a different victim, or a race with an attacker who guesses
+ *     our X25519 pub. Envelope without matching code → ignored.
+ *   - Envelope is short-lived in the mailbox: we DELETE on first decrypt
+ *     and the relay node has its own TTL.
+ */
+import React, { useCallback, useEffect, useRef, useState } from 'react';
+import {
+  View, Text, Pressable, ActivityIndicator, ScrollView,
+} from 'react-native';
+import { router } from 'expo-router';
+import { Ionicons } from '@expo/vector-icons';
+import * as Clipboard from 'expo-clipboard';
+import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import nacl from 'tweetnacl';
+
+import { useStore } from '@/lib/store';
+import { bytesToHex, decryptMessage } from '@/lib/crypto';
+import { fetchInbox } from '@/lib/api';
+import { saveKeyFile, markDeviceRegistered } from '@/lib/storage';
+import { safeBack } from '@/lib/utils';
+import type { KeyFile } from '@/lib/types';
+
+// Protocol constant — bump if payload shape changes.
+const PAIR_ENVELOPE_VERSION = 1;
+
+interface PairEnvelopePayload {
+  v:             number;
+  type:          'pair-handshake';
+  code:          string;
+  master_pub:    string;   // Ed25519 pub, hex
+  master_priv:   string;   // Ed25519 priv, hex
+  master_x25519_pub: string;  // primary device's x25519 pub, hex (for nothing special — just FYI)
+}
+
+function randomCode(): string {
+  // Six decimal digits. Entropy ~20 bits. Good enough for a one-shot
+  // rendezvous code gated by an out-of-band delivery channel (envelope
+  // targeted at a freshly-generated X25519 pub that only this device
+  // holds the priv for).
+  const n = Math.floor(Math.random() * 1_000_000);
+  return n.toString().padStart(6, '0');
+}
+
+export default function PairScreen() {
+  const insets       = useSafeAreaInsets();
+  const setKeyFile   = useStore(s => s.setKeyFile);
+
+  // One-shot keypair + code for this pairing session. Regenerate only on
+  // manual Retry (unmount+remount).
+  const session = useRef(genSession()).current;
+
+  const [status, setStatus] = useState<'waiting' | 'success' | 'error'>('waiting');
+  const [err,    setErr]    = useState<string | null>(null);
+
+  const copyCode = useCallback(async () => {
+    await Clipboard.setStringAsync(session.code);
+  }, [session.code]);
+
+  const copyPub = useCallback(async () => {
+    await Clipboard.setStringAsync(session.x25519Pub);
+  }, [session.x25519Pub]);
+
+  // Poll mailbox until a matching handshake envelope arrives, or user
+  // backs out. Interval 2.5s — conservative on battery, fine for a
+  // flow the user is staring at for a minute.
+  useEffect(() => {
+    let cancelled = false;
+    let timer: ReturnType<typeof setTimeout> | null = null;
+
+    const tick = async () => {
+      if (cancelled) return;
+      try {
+        const envs = await fetchInbox(session.x25519Pub);
+        for (const env of envs) {
+          // Decrypt each envelope with our session priv. We don't know
+          // the primary's x25519 pub up front — it's inside the envelope
+          // metadata. decryptMessage needs both pubs, so we pass the
+          // envelope's sender_pub directly.
+          const plain = decryptMessage(
+            env.ciphertext, env.nonce, env.sender_pub, session.x25519Priv,
+          );
+          if (!plain) continue;
+          let payload: PairEnvelopePayload;
+          try {
+            payload = JSON.parse(plain);
+          } catch { continue; }
+          if (
+            payload.v !== PAIR_ENVELOPE_VERSION ||
+            payload.type !== 'pair-handshake' ||
+            payload.code !== session.code ||
+            !payload.master_pub || !payload.master_priv
+          ) continue;
+
+          // Success — materialise a KeyFile and redirect.
+          const kf: KeyFile = {
+            pub_key:     payload.master_pub,
+            priv_key:    payload.master_priv,
+            x25519_pub:  session.x25519Pub,
+            x25519_priv: session.x25519Priv,
+          };
+          await saveKeyFile(kf);
+          // The root layout auto-links us on first boot if needed, but
+          // the primary device already submitted LINK_DEVICE for our
+          // pub as part of the pairing, so the registry is already
+          // correct. Mark ourselves registered so the revoke-detection
+          // branch doesn't spuriously wipe on next launch.
+          await markDeviceRegistered();
+          setKeyFile(kf);
+
+          // Envelope stays in mailbox until relay TTL eviction; the
+          // single-shot handshake is idempotent (saveKeyFile overwrites)
+          // and our session pub won't be polled again after redirect.
+          setStatus('success');
+          setTimeout(() => {
+            if (!cancelled) router.replace('/(app)/chats' as never);
+          }, 600);
+          return;
+        }
+      } catch {
+        /* transient — retry */
+      }
+      if (!cancelled) timer = setTimeout(tick, 2_500);
+    };
+
+    tick();
+    return () => {
+      cancelled = true;
+      if (timer) clearTimeout(timer);
+    };
+  }, [session, setKeyFile]);
+
+  return (
+    <View style={{
+      flex: 1, backgroundColor: '#000000',
+      paddingTop: insets.top + 12,
+      paddingBottom: Math.max(insets.bottom, 20),
+    }}>
+      <ScrollView
+        contentContainerStyle={{ padding: 24 }}
+        showsVerticalScrollIndicator={false}
+      >
+        {/* Header */}
+        <Pressable
+          onPress={() => safeBack('/')}
+          hitSlop={8}
+          style={{ alignSelf: 'flex-start', marginBottom: 20 }}
+        >
+          <Ionicons name="chevron-back" size={28} color="#ffffff" />
+        </Pressable>
+
+        <View style={{ alignItems: 'center', marginBottom: 28 }}>
+          <View style={{
+            width: 80, height: 80, borderRadius: 22,
+            backgroundColor: '#0a0a0a',
+            borderWidth: 1, borderColor: '#1f1f1f',
+            alignItems: 'center', justifyContent: 'center',
+          }}>
+            <Ionicons name="link" size={40} color="#1d9bf0" />
+          </View>
+          <Text style={{
+            color: '#ffffff', fontSize: 22, fontWeight: '800',
+            marginTop: 14, textAlign: 'center',
+          }}>
+            Pair with your other device
+          </Text>
+          <Text style={{
+            color: '#8b8b8b', fontSize: 13, lineHeight: 19,
+            marginTop: 8, textAlign: 'center', maxWidth: 300,
+          }}>
+            On a device where you're already signed in,
+            open Settings → Devices → Link new device,
+            and enter these values.
+          </Text>
+        </View>
+
+        {/* Code */}
+        <View style={{
+          borderRadius: 14,
+          backgroundColor: '#0a0a0a',
+          borderWidth: 1, borderColor: '#1f1f1f',
+          paddingVertical: 18, paddingHorizontal: 16,
+          marginBottom: 14, alignItems: 'center',
+        }}>
+          <Text style={{
+            color: '#5a5a5a', fontSize: 11, fontWeight: '700',
+            textTransform: 'uppercase', letterSpacing: 1.2,
+          }}>
+            1. Code
+          </Text>
+          <Text style={{
+            color: '#ffffff', fontSize: 38, fontWeight: '800',
+            letterSpacing: 6, marginTop: 4, fontFamily: 'monospace',
+          }}>
+            {session.code.slice(0, 3)} {session.code.slice(3)}
+          </Text>
+          <Pressable onPress={copyCode} hitSlop={6} style={{ marginTop: 6 }}>
+            <Text style={{ color: '#1d9bf0', fontSize: 12, fontWeight: '600' }}>
+              Copy code
+            </Text>
+          </Pressable>
+        </View>
+
+        {/* Device key */}
+        <View style={{
+          borderRadius: 14,
+          backgroundColor: '#0a0a0a',
+          borderWidth: 1, borderColor: '#1f1f1f',
+          paddingVertical: 16, paddingHorizontal: 16,
+          marginBottom: 20,
+        }}>
+          <Text style={{
+            color: '#5a5a5a', fontSize: 11, fontWeight: '700',
+            textTransform: 'uppercase', letterSpacing: 1.2,
+          }}>
+            2. Device key
+          </Text>
+          <Text
+            selectable
+            style={{
+              color: '#ffffff', fontSize: 12, fontFamily: 'monospace',
+              marginTop: 6, lineHeight: 17,
+            }}
+          >
+            {session.x25519Pub}
+          </Text>
+          <Pressable onPress={copyPub} hitSlop={6} style={{ marginTop: 8 }}>
+            <Text style={{ color: '#1d9bf0', fontSize: 12, fontWeight: '600' }}>
+              Copy key
+            </Text>
+          </Pressable>
+        </View>
+
+        {/* Status */}
+        <View style={{ alignItems: 'center', minHeight: 56 }}>
+          {status === 'waiting' && (
+            <View style={{ flexDirection: 'row', alignItems: 'center', gap: 10 }}>
+              <ActivityIndicator size="small" color="#1d9bf0" />
+              <Text style={{ color: '#8b8b8b', fontSize: 13 }}>
+                Waiting for your other device…
+              </Text>
+            </View>
+          )}
+          {status === 'success' && (
+            <View style={{ flexDirection: 'row', alignItems: 'center', gap: 10 }}>
+              <Ionicons name="checkmark-circle" size={20} color="#3ba55d" />
+              <Text style={{ color: '#3ba55d', fontSize: 13, fontWeight: '700' }}>
+                Paired. Opening your chats…
+              </Text>
+            </View>
+          )}
+          {status === 'error' && (
+            <Text style={{ color: '#f4212e', fontSize: 13, textAlign: 'center' }}>
+              {err ?? 'Something went wrong. Please retry.'}
+            </Text>
+          )}
+        </View>
+      </ScrollView>
+    </View>
+  );
+}
+
+// ─── session helper ──────────────────────────────────────────────────────
+
+interface PairSession {
+  x25519Pub:  string;  // hex
+  x25519Priv: string;  // hex
+  code:       string;
+}
+
+function genSession(): PairSession {
+  const kp = nacl.box.keyPair();
+  return {
+    x25519Pub:  bytesToHex(kp.publicKey),
+    x25519Priv: bytesToHex(kp.secretKey),
+    code:       randomCode(),
+  };
+}

client-app/app/index.tsx

@@ -346,8 +346,13 @@ export default function WelcomeScreen() {
           {/* CTA — прижата к правому нижнему краю. */}
           <View style={{
             flexDirection: 'row', justifyContent: 'flex-end', gap: 10,
-            paddingHorizontal: 24, paddingBottom: 8,
+            paddingHorizontal: 24, paddingBottom: 8, flexWrap: 'wrap',
           }}>
+            <CTASecondary
+              label="Pair"
+              icon="link"
+              onPress={() => router.push('/(auth)/pair' as never)}
+            />
             <CTASecondary
               label="Import"
               onPress={() => router.push('/(auth)/import' as never)}

client-app/lib/api.ts

@@ -365,6 +365,25 @@ export interface IdentityInfo {
   x25519_pub: string;   // hex Curve25519 key; empty string if not published
   nickname:   string;
   registered: boolean;
+  /**
+   * Number of active (non-revoked) devices linked to this master identity
+   * via LINK_DEVICE (v2.2.0). 0 for legacy identities that only published
+   * a single X25519 via REGISTER_KEY — senders should fall back to
+   * `x25519_pub` above and skip the device fan-out path.
+   */
+  device_count?: number;
+}
+
+/**
+ * One active device in an identity's multi-device registry. Returned by
+ * GET /api/devices/{master_pub} as part of `devices[]`. Senders use the
+ * list to fan out one sealed envelope per X25519 pub so all of the
+ * recipient's devices receive the message.
+ */
+export interface DeviceInfo {
+  x25519_pub_key: string;
+  device_name:    string;
+  added_at:       number;  // unix seconds
 }
 
 /**
@@ -409,6 +428,56 @@ export async function getIdentity(pubkeyOrAddr: string): Promise<IdentityInfo |
   }
 }
 
+// ─── Multi-device registry (v2.2.0) ───────────────────────────────────────
+
+interface DevicesResponse {
+  master_pub: string;
+  count:      number;
+  devices:    DeviceInfo[];
+}
+
+/**
+ * GET /api/devices/{master_pub} — all active (non-revoked) device records
+ * for the given master identity. Returns an empty array for a legacy
+ * identity (device_count == 0) or a network error — callers should treat
+ * both the same way and fall back to IdentityInfo.x25519_pub so the
+ * pre-v2.2.0 single-device path keeps working.
+ */
+export async function fetchDevices(masterPub: string): Promise<DeviceInfo[]> {
+  try {
+    const resp = await get<DevicesResponse>(`/api/devices/${masterPub}`);
+    return resp.devices ?? [];
+  } catch {
+    return [];
+  }
+}
+
+/**
+ * Pick the right set of recipient X25519 pubs for a sender's fan-out.
+ * Two paths, in priority order:
+ *
+ *   1. New path — /api/devices returns ≥1 entry. Send to each device.
+ *   2. Legacy path — identity published an X25519 via REGISTER_KEY
+ *      (pre-v2.2.0 clients). Send to just that one.
+ *
+ * Returns an empty array only when the recipient has published nothing
+ * at all — caller must surface "no encryption key" to the user rather
+ * than drop the message on the floor.
+ */
+export async function resolveRecipientKeys(
+  recipientMasterPub: string,
+): Promise<string[]> {
+  const devs = await fetchDevices(recipientMasterPub);
+  if (devs.length > 0) {
+    return devs.map(d => d.x25519_pub_key);
+  }
+  const identity = await getIdentity(recipientMasterPub);
+  if (identity?.x25519_pub) {
+    return [identity.x25519_pub];
+  }
+  return [];
+}
+
 // ─── Contract API ─────────────────────────────────────────────────────────────
 
 /**
@@ -712,6 +781,68 @@ export function buildTransferTx(params: {
   };
 }
 
+/**
+ * LINK_DEVICE transaction — publish a per-device X25519 pub in the
+ * identity's device registry so senders can fan out envelopes across
+ * every active device. Signed by the master Ed25519 (= `from`).
+ *
+ * `deviceName` is a short human label shown in Settings → Devices
+ * (≤ 64 bytes, printable ASCII/UTF-8, no control chars).
+ */
+export function buildLinkDeviceTx(params: {
+  from:        string;  // master Ed25519 pubkey
+  x25519Pub:   string;  // per-device X25519 pubkey (64 hex chars, lowercase)
+  deviceName:  string;
+  privKey:     string;
+}): RawTx {
+  const id        = newTxID();
+  const timestamp = rfc3339Now();
+  const payloadObj = {
+    x25519_pub_key: params.x25519Pub,
+    device_name:    params.deviceName,
+  };
+  const payload = strToBase64(JSON.stringify(payloadObj));
+
+  const canonical = txCanonicalBytes({
+    id, type: 'LINK_DEVICE', from: params.from, to: '',
+    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
+  });
+
+  return {
+    id, type: 'LINK_DEVICE', from: params.from, to: '',
+    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
+    signature: signBase64(canonical, params.privKey),
+  };
+}
+
+/**
+ * UNLINK_DEVICE transaction — revoke a previously-linked device so senders
+ * stop shipping envelopes to its X25519 pub. The revoked device itself,
+ * when it next comes online and sees its own pub in the revoked list,
+ * is expected to wipe local state (master priv + cached chats).
+ */
+export function buildUnlinkDeviceTx(params: {
+  from:       string;   // master Ed25519 pubkey
+  x25519Pub:  string;   // pub to revoke
+  privKey:    string;
+}): RawTx {
+  const id        = newTxID();
+  const timestamp = rfc3339Now();
+  const payloadObj = { x25519_pub_key: params.x25519Pub };
+  const payload = strToBase64(JSON.stringify(payloadObj));
+
+  const canonical = txCanonicalBytes({
+    id, type: 'UNLINK_DEVICE', from: params.from, to: '',
+    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
+  });
+
+  return {
+    id, type: 'UNLINK_DEVICE', from: params.from, to: '',
+    amount: 0, fee: MIN_TX_FEE, payload, timestamp,
+    signature: signBase64(canonical, params.privKey),
+  };
+}
+
 /**
  * CONTACT_REQUEST transaction.
  *

client-app/lib/storage.ts

@@ -14,6 +14,12 @@ const KEYFILE_KEY = 'dchain_keyfile';
 const CONTACTS_KEY = 'dchain_contacts';
 const SETTINGS_KEY = 'dchain_settings';
 const CHATS_KEY = 'dchain_chats';
+// Remembers (locally, per install) that this device's X25519 pub has been
+// successfully linked on-chain at least once. Distinguishes "first boot,
+// not registered yet" from "we were registered and then revoked by another
+// device". The second case triggers self-wipe. Stored in AsyncStorage —
+// if it's missing, we simply re-link.
+const DEVICE_REGISTERED_KEY = 'dchain_device_registered';
 
 /** Save the key file in secure storage (encrypted on device). */
 export async function saveKeyFile(kf: KeyFile): Promise<void> {
@@ -99,3 +105,57 @@ export async function appendMessage(chatId: string, msg: CachedMessage): Promise
   const trimmed = msgs.slice(-500);
   await AsyncStorage.setItem(`${CHATS_KEY}_${chatId}`, JSON.stringify(trimmed));
 }
+
+// ─── Multi-device bookkeeping (v2.2.0) ────────────────────────────────────
+
+/**
+ * isDeviceRegistered returns true if this device has ever successfully
+ * linked its X25519 pub on-chain under the current master identity.
+ * A true-then-absent transition (registered → not in chain's active list)
+ * is interpreted as a remote revoke and triggers self-wipe.
+ */
+export async function isDeviceRegistered(): Promise<boolean> {
+  return (await AsyncStorage.getItem(DEVICE_REGISTERED_KEY)) === '1';
+}
+
+/** markDeviceRegistered is called after a LINK_DEVICE commits or is
+    observed in the registry on startup. */
+export async function markDeviceRegistered(): Promise<void> {
+  await AsyncStorage.setItem(DEVICE_REGISTERED_KEY, '1');
+}
+
+/** clearDeviceRegistered is part of wipeAllLocalState; also called on
+    explicit logout. */
+export async function clearDeviceRegistered(): Promise<void> {
+  await AsyncStorage.removeItem(DEVICE_REGISTERED_KEY);
+}
+
+/**
+ * wipeAllLocalState zeroes out every on-device artifact tied to the
+ * current identity: secure-store key, settings, contacts, chats cache,
+ * registered-device marker. Safe to call multiple times.
+ *
+ * Called in two scenarios:
+ *   1. Explicit "Delete account" in Settings.
+ *   2. Self-detected revoke — the chain says our X25519 pub is no longer
+ *      in the active registry but we previously marked it registered,
+ *      so another device issued UNLINK_DEVICE against us. We must not
+ *      keep using the master priv any more — it still works at the
+ *      crypto level, but the social contract is that we're revoked.
+ */
+export async function wipeAllLocalState(): Promise<void> {
+  // Secure store (key).
+  await SecureStore.deleteItemAsync(KEYFILE_KEY).catch(() => {});
+  // AsyncStorage — enumerate our known keys. We don't clear() the whole
+  // store because a share-provider or other app shard could live there.
+  const ks = await AsyncStorage.getAllKeys();
+  const ours = ks.filter(k =>
+    k === CONTACTS_KEY ||
+    k === SETTINGS_KEY ||
+    k === DEVICE_REGISTERED_KEY ||
+    k.startsWith(`${CHATS_KEY}_`),
+  );
+  if (ours.length > 0) {
+    await AsyncStorage.multiRemove(ours);
+  }
+}

cmd/node/main.go

@@ -878,6 +878,7 @@ func main() {
 		IdentityInfo: func(pubKeyOrAddr string) (*blockchain.IdentityInfo, error) {
 			return chain.IdentityInfo(pubKeyOrAddr)
 		},
+		DevicesOf:    chain.DevicesOf,
 		ValidatorSet: chain.ValidatorSet,
 		SubmitTx: func(tx *blockchain.Transaction) error {
 			if err := engine.AddTransaction(tx); err != nil {

deploy/single/join.sh

@@ -0,0 +1,202 @@
+#!/usr/bin/env bash
+# rejoin.sh — полная переустановка dchain joiner-ноды с нуля.
+# Публичный доступ без Caddy/TLS, без API-токена (на свой страх и риск).
+# Запускать БЕЗ sudo.
+
+set -euo pipefail
+
+# ── КОНФИГ ─────────────────────────────────────────────────────────────
+SEED_HTTP="${SEED_HTTP:-http://62.171.151.182:8082}"
+SEED_P2P_IP="${SEED_P2P_IP:-62.171.151.182}"
+SEED_P2P_PORT="${SEED_P2P_PORT:-4005}"
+REPO_URL="${REPO_URL:-https://git.vsecoder.vodka/vsecoder/dchain.git}"
+WORKDIR="${WORKDIR:-$HOME/dchain}"
+LOCAL_P2P_PORT="${LOCAL_P2P_PORT:-4001}"
+LOCAL_HTTP_PORT="${LOCAL_HTTP_PORT:-8082}"
+# ───────────────────────────────────────────────────────────────────────
+
+log()  { printf '\033[1;34m==>\033[0m %s\n' "$*"; }
+warn() { printf '\033[1;33m!!\033[0m  %s\n' "$*" >&2; }
+die()  { printf '\033[1;31mXX\033[0m  %s\n' "$*" >&2; exit 1; }
+need() { command -v "$1" >/dev/null || die "need $1 installed"; }
+
+# ── 0. Требования ──────────────────────────────────────────────────────
+[[ $EUID -eq 0 ]] && die "don't run as root — use your user account, sudo is used per-command"
+need docker; need git; need curl; need jq
+sudo -v
+
+# ── 1. Снести предыдущее состояние ─────────────────────────────────────
+log "stopping any existing dchain stack & purging volumes"
+if [[ -d "$WORKDIR/deploy/single" ]]; then
+  (cd "$WORKDIR/deploy/single" && sudo docker compose down -v 2>/dev/null) || true
+fi
+sudo docker rm -f dchain_node dchain_caddy dchain 2>/dev/null || true
+mapfile -t stale_vols < <(sudo docker volume ls -q | grep -E '^(dchain|dchain-single)' || true)
+(( ${#stale_vols[@]} > 0 )) && sudo docker volume rm "${stale_vols[@]}" 2>/dev/null || true
+
+# ── 2. Свежий репозиторий ──────────────────────────────────────────────
+log "fetching repo → $WORKDIR"
+if [[ -d "$WORKDIR/.git" ]]; then
+  git -C "$WORKDIR" fetch --all --tags --prune
+  git -C "$WORKDIR" reset --hard origin/main
+else
+  rm -rf "$WORKDIR"
+  git clone "$REPO_URL" "$WORKDIR"
+fi
+cd "$WORKDIR/deploy/single"
+
+# ── 3. keys/ под UID 100 ───────────────────────────────────────────────
+log "preparing keys/ for container UID 100:101"
+mkdir -p keys
+sudo chown 100:101 keys
+sudo chmod 755 keys
+[[ -f keys/node.json ]] && { sudo chown 100:101 keys/node.json; sudo chmod 600 keys/node.json; }
+
+# ── 4. Slim-образ ──────────────────────────────────────────────────────
+log "building dchain image (slim)"
+IMAGE=$(sudo docker build -q -f ../prod/Dockerfile.slim ../..)
+[[ -z "$IMAGE" ]] && die "docker build failed"
+
+# ── 5. Ключ ноды ───────────────────────────────────────────────────────
+if [[ ! -f keys/node.json ]]; then
+  log "generating node identity"
+  sudo docker run --rm --entrypoint /usr/local/bin/client \
+    --user 100:101 \
+    -v "$PWD/keys:/out" \
+    "$IMAGE" \
+    keygen --out /out/node.json
+else
+  log "reusing existing keys/node.json"
+fi
+sudo chown 100:101 keys/node.json
+sudo chmod 600 keys/node.json
+
+# ── 6. peer_id seed'a ──────────────────────────────────────────────────
+log "fetching seed peer_id from $SEED_HTTP/stats"
+SEED_PEER_ID=$(curl -sfL "$SEED_HTTP/stats" | jq -r '.node.peer_id // empty')
+[[ -z "$SEED_PEER_ID" ]] && die "can't reach seed at $SEED_HTTP or peer_id missing"
+log "seed peer_id = $SEED_PEER_ID"
+
+# ── 7. Публичный IP ────────────────────────────────────────────────────
+PUBLIC_IP="${PUBLIC_IP:-$(curl -sfL https://api.ipify.org || true)}"
+[[ -z "$PUBLIC_IP" ]] && die "can't detect public IP; export PUBLIC_IP=x.x.x.x и перезапусти"
+log "public IP = $PUBLIC_IP"
+
+# ── 8. node.env (без токена, без genesis) ──────────────────────────────
+log "writing node.env"
+cp -f node.env.example node.env
+
+# удалить из example'а значения, которые мы хотим держать под своим контролем,
+# чтобы они не перекрыли наши append'ы снизу
+sudo sed -i -E '/^(#\s*)?DCHAIN_(GENESIS|API_TOKEN|API_PRIVATE|JOIN|PEERS|ANNOUNCE|DB|MAILBOX_DB|FEED_DB|REGISTER_RELAY|RELAY_FEE|FEED_DISK_LIMIT_MB|CHAIN_DISK_LIMIT_MB|UPDATE_SOURCE_URL)=/d' node.env
+
+sudo tee -a node.env > /dev/null <<EOF
+
+# ── AUTO-GENERATED BY rejoin.sh ─────────────────────────────────────
+# joiner → seed $SEED_HTTP  (public node, no token)
+DCHAIN_JOIN=$SEED_HTTP
+DCHAIN_PEERS=/ip4/$SEED_P2P_IP/tcp/$SEED_P2P_PORT/p2p/$SEED_PEER_ID
+DCHAIN_ANNOUNCE=/ip4/$PUBLIC_IP/tcp/$LOCAL_P2P_PORT
+
+DCHAIN_DB=/data/chain
+DCHAIN_MAILBOX_DB=/data/mailbox
+DCHAIN_FEED_DB=/data/feed
+
+DCHAIN_REGISTER_RELAY=true
+DCHAIN_RELAY_FEE=1000
+
+DCHAIN_FEED_DISK_LIMIT_MB=4096
+DCHAIN_CHAIN_DISK_LIMIT_MB=20480
+
+DCHAIN_UPDATE_SOURCE_URL=https://git.vsecoder.vodka/api/v1/repos/vsecoder/dchain/releases/latest
+EOF
+
+# ── 9. Compose: прямой проброс 4001+8080 наружу, Caddy снести навсегда ─
+log "patching docker-compose.yml: direct ports, caddy removed"
+python3 - <<PY
+import re, pathlib
+p = pathlib.Path('docker-compose.yml')
+src = p.read_text()
+
+# 9a. Вырезать весь сервис caddy (от "  caddy:" до следующего сервиса
+# того же уровня или конца блока services).
+src = re.sub(
+    r'(?ms)^  caddy:\n(?:(?:    .*\n)|\n)+?(?=^  [A-Za-z_-]+:|\Z)',
+    '', src,
+)
+
+# 9b. Убрать зависимости от caddy, если где-то остались.
+src = re.sub(r'(?m)^\s*-\s*caddy\s*$\n', '', src)
+src = re.sub(r'(?m)^\s*depends_on:\s*\n(\s*-\s*caddy\s*\n)+', '', src)
+
+# 9c. Заставить node светить наружу 4001 (libp2p) и 8080 (HTTP).
+# Ищем первый ports: в сервисе node; если его нет — инжектим.
+m = re.search(r'(?ms)^  node:\n(.*?)(?=^  [A-Za-z_-]+:|\Z)', src)
+if not m:
+    raise SystemExit('no `node:` service in compose')
+node_block = m.group(1)
+
+wanted = f'    ports:\n      - "$LOCAL_P2P_PORT:4001"\n      - "$LOCAL_HTTP_PORT:8080"\n'
+
+if re.search(r'(?m)^    ports:', node_block):
+    # Заменить существующий блок ports целиком
+    node_block_new = re.sub(
+        r'(?ms)^    ports:\n(?:      -.*\n)+',
+        wanted, node_block,
+    )
+else:
+    # Добавить сразу после строки "container_name:" (или restart:)
+    node_block_new = re.sub(
+        r'(?m)^(    (?:container_name|restart):.*\n)',
+        r'\\1' + wanted, node_block, count=1,
+    )
+    if node_block_new == node_block:  # fallback — в начало блока
+        node_block_new = wanted + node_block
+
+src = src[:m.start(1)] + node_block_new + src[m.end(1):]
+
+# 9d. Убрать блок expose у node — не нужен, раз ports наружу.
+src = re.sub(
+    r'(?ms)^    expose:\n(?:      -.*\n)+', '', src,
+)
+
+p.write_text(src)
+PY
+
+# ── 10. Подъём ─────────────────────────────────────────────────────────
+log "docker compose up -d"
+sudo docker compose up -d --build
+
+# ── 11. Sanity checks ──────────────────────────────────────────────────
+sleep 3
+log "sanity checks (дай ~30 сек чтобы healthcheck подхватился):"
+set +e
+echo "──── docker compose ps ────"
+sudo docker compose ps
+echo "──── docker logs dchain_node | tail ────"
+sudo docker logs --tail 30 dchain_node 2>&1
+echo "──── /api/netstats ────"
+curl -s "http://localhost:$LOCAL_HTTP_PORT/api/netstats" | jq '.'
+echo "──── seed height (для сверки) ────"
+curl -s "$SEED_HTTP/api/netstats" | jq '.total_blocks'
+
+cat <<EOM
+
+======================================================================
+✓ Готово. Нода публичная, без токена и без TLS.
+
+  API:
+    http://$PUBLIC_IP:$LOCAL_HTTP_PORT/api/netstats
+    http://$PUBLIC_IP:$LOCAL_HTTP_PORT/swagger
+
+  Следи за sync'ом:
+    sudo docker logs -f dchain_node | grep -E 'applied|height|peer'
+
+  Повторный полный сброс:
+    ./rejoin.sh
+
+  Открой в firewall/security-group на этом VPS:
+    - $LOCAL_P2P_PORT/tcp (libp2p)
+    - $LOCAL_HTTP_PORT/tcp (HTTP API)
+======================================================================
+EOM

docs/ROADMAP.md

@@ -0,0 +1,219 @@
+# Roadmap
+
+Living doc — «куда идём дальше». Два активных вектора: **v2.2.0 multi-device**
+и **desktop Electron client**. Всё что tentative — помечено `?`; всё что
+решено и принято к работе — без знаков.
+
+---
+
+## v2.2.0 — Multi-device (per-device X25519, on-chain device registry)
+
+### Проблема
+
+Сейчас у пользователя одна пара X25519 (хранится в `keyFile`), и relay-mailbox —
+queue с DELETE-после-чтения. При двух устройствах:
+
+- Конверт забирает то устройство, что первое дёрнуло `/relay/inbox` — второе
+  теряет сообщение навсегда.
+- История чатов per-device, не синхронизируется (`AsyncStorage` на каждом
+  устройстве свой).
+
+On-chain часть (posts, follows, tx, wallet) работает нормально — оба устройства
+читают один чейн и видят одно и то же. Чинить надо только мессенджер.
+
+### Решение — путь А (Signal-style): X25519 на устройство + device registry
+
+1. **Master identity = Ed25519** (как сейчас). Подписывает tx, владеет
+   балансом, — один на всю identity.
+2. **X25519 — per-device**. Каждое устройство при первом старте генерит
+   свою пару. Relay-mailbox остаётся queue'ом, но адресуется по
+   **устройству**, не по identity.
+3. **Device registry on-chain**: новые tx-типы `LINK_DEVICE` / `UNLINK_DEVICE`,
+   подписываются master Ed25519, публикуют/отзывают связку
+   `(master_pub → device_x25519_pub, device_name)`.
+4. **Sender-side fan-out**: при отправке — один envelope на каждое
+   активное устройство получателя. Мессадж → N конвертов.
+5. **Revoke**: master подписывает `UNLINK_DEVICE`, клиент, обнаруживший
+   свой `x25519_pub` в revoked — wipe'ит локальную БД (zeroize master
+   Ed25519 + delete chats).
+
+### План работ (PR-by-PR)
+
+#### PR #1 — Chain-side (backend) — _v2.2.0-alpha1_
+
+- [ ] `blockchain/types.go`: `EventLinkDevice`, `EventUnlinkDevice`
+  + payload structs `LinkDevicePayload`, `UnlinkDevicePayload`.
+- [ ] `blockchain/chain.go`: applyTx-ветки, state persistence:
+  - `prefixDevice + x25519_pub → DeviceRecord{owner, name, added_at, revoked_at?}`.
+  - Обратный индекс `prefixDevicesByOwner + master_pub → [x25519_pub, …]`.
+- [ ] Константа `MaxDevicesPerOwner = 10`.
+- [ ] Validation:
+  - Tx подписана master'ом; подпись matches `payload.Owner`.
+  - `x25519_pub` уникален в registry (не занят другим master'ом).
+  - `device_name` ≤ 64 символов; printable.
+  - При `UNLINK_DEVICE`: запись существует, owner совпадает с signer'ом.
+- [ ] HTTP: `GET /api/devices/{master_pub}` → `[{x25519_pub, device_name, added_at}, …]`,
+  фильтрует revoked.
+- [ ] В `/api/identity/{pub}` добавить поле `device_count`.
+- [ ] Unit-тесты:
+  - Happy path link + list.
+  - Unlink → list сократился.
+  - Лимит `MaxDevicesPerOwner`.
+  - Чужая подпись → reject.
+  - Duplicate x25519_pub → reject.
+- [ ] Swagger + `docs/api/devices.md`.
+
+Совместимость: старые клиенты, которые не обновили identity, продолжают
+работать по old-schema (envelope на published X25519 из identity). Sender
+fall-back'ит на identity.x25519, если `device_count == 0`.
+
+#### PR #2 — Client fan-out (mobile) — _v2.2.0-alpha2_
+
+- [ ] `lib/api.ts`: `fetchDevices(masterPub): Promise<DeviceRecord[]>`,
+  с кэшем в zustand store + инвалидацией по WS-ивенту `tx:LINK_DEVICE|UNLINK_DEVICE`.
+- [ ] `chats/[id].tsx` → `sendCore`: `Promise.all` по `devices[]`;
+  если `devices.length == 0` — fall-back на identity.x25519 (legacy path).
+- [ ] При первом старте (онбординг): если identity ещё не зарегистрирована —
+  `PUBLISH_KEY` tx + `LINK_DEVICE` tx (**этот** девайс как первый в списке).
+- [ ] UI: в chat-list tile бейдж `2/2` на своих сообщениях (доставлено
+  на N устройств получателя).
+- [ ] Тест: два клиента на одну identity, отправляем на contact — оба
+  получают.
+
+#### PR #3 — Devices screen + pairing flow (mobile + desktop) — _v2.2.0-alpha3_
+
+- [ ] Settings → **Devices**: список активных, unlink-кнопка у каждого
+  (кроме `this device`).
+- [ ] «Link new device» flow:
+  - Новое устройство генерит свой X25519, показывает QR
+    `{x25519_pub, device_name, nonce, rendezvous_id}`.
+  - Старое сканирует → Confirm → подписывает `LINK_DEVICE` tx +
+    шлёт через relay envelope `{master_ed25519_priv, recent_history}` —
+    encrypted for new device's X25519, TTL ≤ 60 сек.
+  - Новое читает envelope, сохраняет master + history, готово.
+- [ ] Self-wipe при обнаружении своего `x25519_pub` в revoked:
+  zeroize master, clear AsyncStorage/keychain, redirect на onboarding.
+
+#### PR #4 — Desktop Electron shell — _v2.2.0-rc1_
+
+См. отдельный раздел ниже.
+
+### Нерешённые вопросы
+
+- **QR-pairing UX на desktop'е**: у ноутбука камеры часто нет. Вариант:
+  master на phone шлёт invite-envelope по pre-shared secret (6-digit code,
+  вводится в обе стороны), без QR. Подумать после PR #2.
+- **History-sync backup формат**: JSON export всей ChatStorage shreds'ов?
+  Ограничение по размеру? TTL у backup-конверта? — в PR #3.
+- **Revoked-device-wipe race**: если устройство оффлайн 6 месяцев, потом
+  поднимается — первое что видит это свой revoked. Должен успеть wipe'нуться
+  **до** попытки послать tx с master-ключом. Продумать порядок bootstrap'а.
+
+---
+
+## Desktop client (Electron)
+
+Цель: 1:1 функциональный паритет с мобильным, десктопная эргономика, keyboard-first.
+
+### Архитектура
+
+- **Electron** + **React (Vite)** + **TypeScript**.
+- 80% `lib/` переиспользуется из `client-app/lib/` (api, feed, crypto, store, types).
+- Нативные модули: `electron-store` (+ `safeStorage`) для keys, `clipboard`,
+  `Notification`, `dialog.showOpenDialog`.
+- Custom title bar (frame-less), 3-panel layout.
+
+### Экраны
+
+Full design — `docs/desktop-design.md` (TODO). Sections:
+
+- **Messages** — список чатов + conversation panel. Saved Messages pinned top.
+- **Feed** — tabs (For You / Following / Trending 24h / 7d / Hashtag) +
+  post list + thread panel.
+- **Wallet** — account overview + tx history + tx detail.
+- **Contacts** — grouped list (All / Online / Blocked / Requests) + contact profile.
+- **Settings** — grouped: Node, Identity, **Devices**, Privacy, Feed, Notifications,
+  Advanced, About.
+- **Profile** (внизу nav) — self profile; чужой — в detail pane.
+- **Auth/Onboarding** — Welcome / Create / Import / Pair-with-phone (QR/code).
+
+### Стилистика (переносим)
+
+Чёрный `#000`, карточки `#0a0a0a`, бордеры `#1f1f1f`, текст `#fff`/`#8b8b8b`.
+Синий accent `#1d9bf0`, оранж warning `#f0b35a`. Синий bookmark-avatar для Saved Messages.
+
+### Не переносим
+
+Все React-Native-анимации (Pressable-animations, `scaleY: -1`, gesture-handler
+long-press). На десктопе — правый клик, hover-states, keyboard shortcuts,
+обычный scroll вместо inverted FlatList.
+
+### Global keybinds
+
+| Key | Action |
+|---|---|
+| `Ctrl/Cmd+1..5` | Переключение секций |
+| `Ctrl/Cmd+N` | Новый пост / новый контакт (контекстно) |
+| `Ctrl/Cmd+K` | Global search |
+| `Ctrl/Cmd+F` | Search в текущей list pane |
+| `Ctrl/Cmd+,` | Settings |
+| `Ctrl/Cmd+Enter` | Send (chat / publish post) |
+| `Esc` | Close modal / cancel selection |
+
+### Структура папок
+
+```
+desktop/
+├── electron/
+│   ├── main.ts          # BrowserWindow, IPC, auto-update
+│   ├── preload.ts       # contextBridge — safe API
+│   ├── menu.ts          # native menu bar
+│   └── deep-link.ts     # dchain:// protocol handler
+├── src/                 # renderer
+│   ├── App.tsx
+│   ├── shell/           # nav, status bar, title bar
+│   ├── sections/
+│   │   ├── messages/
+│   │   ├── feed/
+│   │   ├── wallet/
+│   │   ├── contacts/
+│   │   ├── settings/
+│   │   └── profile/
+│   ├── modals/
+│   ├── auth/
+│   ├── lib/             # reuse из client-app/lib
+│   └── styles/
+└── package.json
+```
+
+### План работ (отдельно, после v2.2.0-alpha3)
+
+- [ ] Boilerplate: Electron + Vite + React + TS, frame-less window, 3-panel shell.
+- [ ] Сопрягание `lib/` из client-app (заменить expo-* на Electron-эквиваленты).
+- [ ] Sections по порядку: Messages → Feed → Wallet → Contacts → Settings → Profile.
+- [ ] Multi-device pairing flow (использует v2.2.0 registry).
+- [ ] Auto-update через electron-updater или через тот же `/api/update-check`.
+- [ ] Packaging: `electron-builder` → `.dmg`, `.exe`, `.AppImage`, `.deb`.
+
+### Открытые вопросы (desktop)
+
+- **Auto-update channel**: гнать через Gitea releases (как node) или отдельный S3/Gitea-attachments?
+- **Sandbox**: desktop хранит master Ed25519 — обязательно `safeStorage` (macOS Keychain, Windows DPAPI, libsecret на Linux). На Linux без libsecret — fallback на plaintext + warning.
+- **Deep-link**: `dchain://chat/<pub>` для шаринга профилей/постов из браузера.
+
+---
+
+## Меньшие хвосты (неприоритетно)
+
+- `prev_hash mismatch` при двойной gossip-доставке — понизить до Debug уровня,
+  не пугать операторов (см. history с joiner-node bring-up).
+- `/api/network-info.peers` у seed'а возвращает `[]` если
+  `DCHAIN_ANNOUNCE` не задан — добавить fallback:
+  если announce пустой, публиковать *первый listen-addr + свой peer_id*
+  (не `127.0.0.1`), чтобы joiner'ы не упирались в `peers:[]`.
+- **Groups (3+ участников)** в чатах — тип `Contact.kind == 'group'`
+  в клиенте есть, а на backend'е не реализован. После v2.2.0, потому что
+  pairwise messaging ↔ group messaging на multi-device — это другой
+  математический слой (MLS или Sender Keys).
+- Repa как weight в selection-lider PBFT — сейчас только scoring; для
+  настоящего proof-of-reputation нужно переписать leader-rotation.

node/api_explorer.go

@@ -510,10 +510,63 @@ func apiIdentity(q ExplorerQuery) http.HandlerFunc {
 			jsonErr(w, err, 500)
 			return
 		}
+		// Multi-device (v2.2.0): stuff the active device count into the
+		// identity payload so a sender can decide upfront whether to
+		// fan out envelopes or fall back to the legacy single-X25519
+		// path (device_count == 0).
+		if q.DevicesOf != nil {
+			if devs, derr := q.DevicesOf(pubKey); derr == nil {
+				info.DeviceCount = len(devs)
+			}
+		}
 		jsonOK(w, info)
 	}
 }
 
+// apiDevices — GET /api/devices/{master_pub_or_addr}
+//
+// Returns the active (non-revoked) devices linked to a master Ed25519
+// identity. Used by senders to fan out one envelope per device. Legacy
+// identities (count=0) should be handled by the caller by falling back
+// to IdentityInfo.X25519Pub — this endpoint is strictly the new registry.
+func apiDevices(q ExplorerQuery) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		input := strings.TrimPrefix(r.URL.Path, "/api/devices/")
+		input = strings.Trim(input, "/")
+		if input == "" {
+			jsonErr(w, fmt.Errorf("master pubkey or address required"), 400)
+			return
+		}
+		if q.DevicesOf == nil {
+			jsonErr(w, fmt.Errorf("device registry not available"), 503)
+			return
+		}
+		pubKey, err := resolveAccountID(q, input)
+		if err != nil {
+			jsonErr(w, err, 404)
+			return
+		}
+		recs, err := q.DevicesOf(pubKey)
+		if err != nil {
+			jsonErr(w, err, 500)
+			return
+		}
+		out := make([]blockchain.DeviceInfo, 0, len(recs))
+		for _, rec := range recs {
+			out = append(out, blockchain.DeviceInfo{
+				X25519PubKey: rec.X25519PubKey,
+				DeviceName:   rec.DeviceName,
+				AddedAt:      rec.AddedAt,
+			})
+		}
+		jsonOK(w, map[string]any{
+			"master_pub": pubKey,
+			"count":      len(out),
+			"devices":    out,
+		})
+	}
+}
+
 func apiSubmitTx(q ExplorerQuery) http.HandlerFunc {
 	// The returned handler is wrapped in withSubmitTxGuards() by the caller:
 	// body size is capped at MaxTxRequestBytes and per-IP rate limiting is

node/api_routes.go

@@ -53,6 +53,10 @@ type ExplorerQuery struct {
 	NetStats         func() (blockchain.NetStats, error)
 	RegisteredRelays func() ([]blockchain.RegisteredRelayInfo, error)
 	IdentityInfo     func(pubKeyOrAddr string) (*blockchain.IdentityInfo, error)
+	// DevicesOf (multi-device v2.2.0) returns the identity's non-revoked
+	// device records. Empty slice if the identity hasn't linked any yet
+	// — senders fall back to IdentityInfo.X25519Pub for legacy clients.
+	DevicesOf        func(masterPub string) ([]blockchain.DeviceRecord, error)
 	ValidatorSet     func() ([]string, error)
 	SubmitTx         func(tx *blockchain.Transaction) error
 	// ConnectedPeers (optional) returns the local libp2p view of currently
@@ -222,6 +226,7 @@ func registerExplorerAPI(mux *http.ServeMux, q ExplorerQuery) {
 	mux.HandleFunc("/api/node/", apiNode(q))           // GET /api/node/{pubkey|DC...}
 	mux.HandleFunc("/api/relays", apiRelays(q))        // GET /api/relays
 	mux.HandleFunc("/api/identity/", apiIdentity(q))   // GET /api/identity/{pubkey|addr}
+	mux.HandleFunc("/api/devices/", apiDevices(q))     // GET /api/devices/{master_pub} — multi-device registry (v2.2.0)
 	mux.HandleFunc("/api/validators", apiValidators(q))// GET /api/validators
 	mux.HandleFunc("/api/tx", withWriteTokenGuard(withSubmitTxGuards(apiSubmitTx(q)))) // POST /api/tx (body size + per-IP rate limit + optional token gate)
 	// Live event stream (SSE) — GET /api/events