Add Silent Payments (BIP-352) sending

Pay sp1… addresses: the wallet derives the one-time taproot output from the
recipient's address + the transaction's own input keys (ECDH), so payments are
unlinkable on-chain with no interaction. New src/silentpay.js implements the
sender derivation + bech32m address decode, validated against the official
BIP-352 test vectors (all P2WPKH-input / single-recipient cases pass; the rest
exercise input types Hal never spends).

buildTx detects sp1… recipients, selects coins against a same-size placeholder
taproot output, then swaps in the script derived from the final input set
(updateOutput). Works for normal sends, multi-recipient, and send-max. The
review screen shows the sp1… address with a 'Silent payment' label (the on-chain
output is a derived one-time taproot address). End-to-end signing verified.

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

1 files changed, 10 insertions, 2 deletions

diff --git a/src/app.js b/src/app.js
index 21aea3d..d7fbc4e 100644
--- a/src/app.js
+++ b/src/app.js
@@ -9,6 +9,7 @@ import { qrSvg } from './qr.js';
 import { scanQr } from './scan.js';
 import { getSyncConfig, setSyncConfig } from './nostr.js';
 import { getExplorerConfig, setExplorerConfig, EXPLORER_PRESETS, getRealtimeEnabled, setRealtimeEnabled } from './api.js';
+import { isSilentPaymentAddress } from './silentpay.js';
 import { t, LANGS, getLang, setLang, isRTL, loadLocale } from './i18n.js';
 import {
   fmtBtc,
@@ -2155,7 +2156,9 @@ function recipientRow(s, r, i) {
   const check = h('div', { class: 'addr-check' });
   const syncCheck = () => {
     const a = r.address.trim();
-    check.replaceChildren(...addrVerifyNodes(a));
+    const nodes = addrVerifyNodes(a);
+    if (a && isSilentPaymentAddress(a)) nodes.push(h('span', { class: 'small faint', style: 'margin-left:6px' }, '· ' + t('silentPaymentNote')));
+    check.replaceChildren(...nodes);
     check.style.display = a ? '' : 'none';
   };
 
@@ -2382,7 +2385,12 @@ function reviewView() {
       { class: 'summary col', style: 'gap:0' },
       ...outs.map((o) =>
         h('div', { class: 'line' },
-          h('span', { class: 'k mono break' }, shortAddr(o.address, 14, 8)),
+          o.silent
+            ? h('span', { class: 'k col', style: 'gap:2px;align-items:flex-start' },
+                h('span', { class: 'mono break' }, shortAddr(o.silent, 12, 8)),
+                h('span', { class: 'small faint' }, t('silentPaymentNote'))
+              )
+            : h('span', { class: 'k mono break' }, shortAddr(o.address, 14, 8)),
           h('span', { class: 'v' }, fmtAmount(o.amount), ' ', unitTag())
         )
       ),