Rebuild as single-file offline BIP84 wallet

Replace the SvelteKit/daisyUI prototype with a vanilla JS + hand-rolled CSS
app that Bun bundles (code + scure/noble crypto + QR + CSS) into one
self-contained dist/index.html runnable offline from file://.

Wallet core (src/wallet.js):
- BIP84 native-segwit HD wallet from BIP39 seed (+optional passphrase)
- gap-limit scan of receive/change chains, aggregate balance, tx history
- fresh receive/change addresses; signs with witnessUtxo only (enables
  offline signing with no prev-tx fetch)
- coin selection + fee estimation via btc-signer selectUTXO; send-max;
  manual coin control
- offline JSON snapshot export/import (keyless) + signed-tx hex/QR export
- realtime mempool.space WebSocket: track-addresses -> debounced auto
  refresh of balances/history (no polling); live status badge

UI (src/app.js): clean light paper-wallet; create (with optional, skippable
backup verification) / import flow; receive (QR) / send / history / coins /
tools tabs; clickable logo returns home.

API (src/api.js): mempool.space wrapper with retry/backoff for scan-burst
rate limiting; single network choke-point for offline enforcement.

Verified: BIP84 spec vectors, build/sign/parse for auto/max/manual flows,
snapshot roundtrip, live scan + WebSocket, headless-Chrome UI smoke tests.

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

1 files changed, 56 insertions, 0 deletions

diff --git a/src/format.js b/src/format.js
new file mode 100644
index 0000000..6191033
--- /dev/null
+++ b/src/format.js
@@ -0,0 +1,56 @@
+// Small formatting helpers. Internally amounts are integer satoshis (Number;
+// safe because max BTC supply ~2.1e15 sats < Number.MAX_SAFE_INTEGER).
+
+export const SATS = 100_000_000;
+
+export function btc(sats) {
+  return (Number(sats) / SATS).toFixed(8);
+}
+
+// "0.01234500" with the trailing-zero portion dimmed is done in CSS; here we
+// just produce a clean fixed-8 string.
+export function fmtBtc(sats) {
+  return btc(sats);
+}
+
+export function fmtSats(sats) {
+  return Number(sats).toLocaleString('en-US');
+}
+
+export function fmtUsd(sats, price) {
+  if (!price) return '';
+  const usd = (Number(sats) / SATS) * price;
+  return usd.toLocaleString('en-US', { style: 'currency', currency: 'USD' });
+}
+
+// Parse a user-entered amount. Accepts BTC (default) or sats.
+export function parseAmount(value, unit) {
+  const n = Number(String(value).trim().replace(/,/g, ''));
+  if (!isFinite(n) || n < 0) return null;
+  return unit === 'sats' ? Math.round(n) : Math.round(n * SATS);
+}
+
+export function shortAddr(a, head = 10, tail = 8) {
+  if (!a || a.length <= head + tail + 1) return a;
+  return `${a.slice(0, head)}…${a.slice(-tail)}`;
+}
+
+export function shortTxid(t) {
+  return shortAddr(t, 8, 8);
+}
+
+export function timeAgo(unixSeconds) {
+  if (!unixSeconds) return 'pending';
+  const s = Math.max(0, Math.floor(Date.now() / 1000 - unixSeconds));
+  const units = [
+    [31536000, 'y'],
+    [2592000, 'mo'],
+    [86400, 'd'],
+    [3600, 'h'],
+    [60, 'm'],
+  ];
+  for (const [secs, label] of units) {
+    if (s >= secs) return `${Math.floor(s / secs)}${label} ago`;
+  }
+  return `${s}s ago`;
+}