Reduce gap limit to 5; clarify receive-address note

Since the wallet only ever exposes one unused receive address at a time,
used addresses stay contiguous (gap never exceeds 1), so a gap limit of 5 is
a safe margin and cuts a scan from ~40 to ~10 requests.

Also reword the receive note: the address advances automatically (via the
realtime WebSocket) when paid, so drop the confusing "scan again".

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

2 files changed, 8 insertions, 2 deletions

diff --git a/src/app.js b/src/app.js
index 7f15c96..378eddd 100644
--- a/src/app.js
+++ b/src/app.js
@@ -506,7 +506,7 @@ function receiveTab() {
     ),
     h('div', { class: 'path' }, `m/84'/${coin}'/0'/0/${fresh.index}`),
     h('p', { class: 'small muted center', style: 'margin:0' },
-      'A fresh address is shown for better privacy. After a payment arrives, scan again to advance to a new one.'),
+      'A fresh address is shown for better privacy. When it receives a payment, a new one appears automatically.'),
     addressBook()
   );
 }
diff --git a/src/wallet.js b/src/wallet.js
index 04f303a..21fbcf2 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -17,7 +17,13 @@ import { p2wpkh } from '@scure/btc-signer/payment';
 
 import { Api, pool } from './api.js';
 
-const GAP_LIMIT = 20; // BIP44 standard gap limit
+// The BIP44 standard gap limit is 20, but that means ~40 address lookups per
+// scan. We can safely use a much smaller limit because this wallet only ever
+// exposes ONE unused receive address at a time (freshReceive = first unused;
+// there is no "generate another address" button). That keeps used addresses
+// contiguous, so the gap between them is never more than 1 — a limit of 5 is a
+// comfortable safety margin while cutting scan requests ~4x.
+const GAP_LIMIT = 5;
 
 const NETS = {
   mainnet: { net: btc.NETWORK, coin: 0 },