fix: chain sync batch — testnet xpub collisions, decline/invalid handling

- Drop the cross-chain duplicate-xpub rejection: all testnets share slip 1,
  so Sepolia and Amoy (both evm/p2sh with default bip32 bytes) derive
  byte-identical wallet xpubs — as do Testnet and Signet Bitcoin. Any batch
  containing such a pair was rejected wholesale as 'duplicate_xpub'.
  Duplicate CHAIN entries remain invalid.
- Post chainsyncrejected('invalid') for malformed requests instead of
  silently dropping them — the wallet otherwise waits the full 30s fallback
  timeout before offering per-chain QR sync. This wires up the previously
  dead 'invalid' rejection-reason arm.
- Declining a batch left batchStartedRef stuck true for the session
  (suppressing every later verification code) and, on a fresh pairing,
  dropped the identity verification code entirely while the wallet shows
  one. Decline now shows the identity code and resets the flag.
- CHAIN_SYNC_POST_SPACING_MS 1500 → 3000: the relay sync doc is
  last-write-wins per walletIdentity and the wallet polls at 1s — 1.5s left
  almost no margin for network jitter on already-derived chains, and a
  missed doc is never re-posted. 3s gives the poll 2-3 chances per doc and
  stays far inside the wallet's 60s stall window.

Author: TheTrunk

src/lib/chainSyncRequest.ts

@@ -26,9 +26,12 @@ export const CHAIN_SYNC_MAX_CHAINS = 20;
 /**
  * Spacing between per-chain POST /v1/sync calls. The relay sync document is
  * last-write-wins keyed on walletIdentity and the wallet polls it every 1s —
- * posting faster than the poll interval could make the wallet miss a chain.
+ * posting faster than the poll interval makes the wallet miss a chain. 3s
+ * gives the poll 2-3 chances per document (1.5s left almost no margin for
+ * network jitter on already-derived chains, and a missed doc is never
+ * re-posted); still far inside the wallet's 60s per-chain stall window.
  */
-export const CHAIN_SYNC_POST_SPACING_MS = 1500;
+export const CHAIN_SYNC_POST_SPACING_MS = 3000;
 
 const MAX_XPUB_LENGTH = 3000; // solana pubkey arrays are ~950 chars; xpubs ~112
 
@@ -114,7 +117,6 @@ export function parseChainSyncRequest(
     return { status: 'invalid', reason: 'too_many_chains' };
   }
   const seen = new Set<string>();
-  const seenXpubs = new Set<string>();
   const entries: ChainSyncRequestEntry[] = [];
   for (const item of chains) {
     if (!item || typeof item !== 'object' || Array.isArray(item)) {
@@ -148,12 +150,10 @@ export function parseChainSyncRequest(
     if (!xpubValid) {
       return { status: 'invalid', reason: 'bad_xpub' };
     }
-    // Each chain derives a distinct extended key; the same xpub on two
-    // chains is never produced by a well-formed wallet.
-    if (seenXpubs.has(xpubWallet)) {
-      return { status: 'invalid', reason: 'duplicate_xpub' };
-    }
-    seenXpubs.add(xpubWallet);
+    // NOTE: the same xpub CAN legitimately appear on two different chains —
+    // all testnets share slip 1, so e.g. Sepolia and Amoy (both p2sh/evm,
+    // default bip32 bytes) derive byte-identical xpubs. Only duplicate CHAIN
+    // entries are invalid (checked above).
     entries.push({
       chain: chain as keyof cryptos,
       xpubWallet,

src/screens/Home/Home.tsx

@@ -489,6 +489,15 @@ function Home({ navigation }: Props) {
     }
     console.log('[Chain Sync] Invalid request:', parsed.reason);
     displayMessage('error', t('home:err_invalid_request'));
+    // Tell the wallet immediately — without this it waits out the full 30s
+    // fallback timeout before offering per-chain QR sync.
+    postAction(
+      'chainsyncrejected',
+      buildChainSyncRejectionPayload('invalid'),
+      identityChain,
+      '',
+      sspWalletKeyInternalIdentity,
+    ).catch((error) => console.log(error));
   };
 
   const handleChainSyncRequestAction = (status: boolean) => {
@@ -497,6 +506,16 @@ function Home({ navigation }: Props) {
     } else {
       // reject — notify wallet so it can offer per-chain QR sync right away
       setChainSyncData(null);
+      // The declined batch will never drive the code screen. If identity was
+      // paired this session, show its code now (the wallet shows one), and
+      // clear the batch flag so a later pairing starts clean — leaving it set
+      // would suppress every future identity code this session.
+      batchStartedRef.current = false;
+      if (identityVerifyEntryRef.current) {
+        setBatchVerifyWords(
+          sessionVerificationWords([identityVerifyEntryRef.current]),
+        );
+      }
       postAction(
         'chainsyncrejected',
         buildChainSyncRejectionPayload('declined'),

tests/lib/chainSyncRequest.test.ts

@@ -185,17 +185,23 @@ describe('parseChainSyncRequest', () => {
     expect(result).toEqual({ status: 'invalid', reason: 'duplicate_chain' });
   });
 
-  it('rejects the same xpub reused across different chains', () => {
+  it('accepts the same xpub on two different chains (testnets share slip 1 and derive identical xpubs)', () => {
     const result = parseChainSyncRequest(
       payload({
         chains: [
-          { chain: 'eth', xpubWallet: VALID_XPUB },
-          { chain: 'polygon', xpubWallet: VALID_XPUB },
+          { chain: 'sepolia', xpubWallet: VALID_XPUB },
+          { chain: 'amoy', xpubWallet: VALID_XPUB },
         ],
       }),
       IDENTITY_CHAIN,
     );
-    expect(result).toEqual({ status: 'invalid', reason: 'duplicate_xpub' });
+    expect(result.status).toBe('ok');
+    if (result.status === 'ok') {
+      expect(result.request.chains.map((c) => c.chain)).toEqual([
+        'sepolia',
+        'amoy',
+      ]);
+    }
   });
 
   it('rejects missing/empty/oversized xpubs', () => {