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, 53 insertions, 0 deletions

diff --git a/build.js b/build.js
new file mode 100644
index 0000000..486908e
--- /dev/null
+++ b/build.js
@@ -0,0 +1,53 @@
+// Build a single, self-contained dist/index.html.
+//
+// Everything — app code, the @scure/@noble crypto libs, the QR generator, and
+// all CSS — is bundled and inlined so the result is one file you can save and
+// open offline straight from the filesystem (file://). No server, no network.
+
+import { mkdir } from 'node:fs/promises';
+
+const FAVICON =
+  'data:image/svg+xml,' +
+  encodeURIComponent(
+    `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><rect width="32" height="32" rx="7" fill="#f7931a"/><text x="16" y="23" font-size="20" font-family="Arial" font-weight="bold" text-anchor="middle" fill="#fff">₿</text></svg>`
+  );
+
+export async function buildHtml({ minify = true } = {}) {
+  const result = await Bun.build({
+    entrypoints: ['./src/app.js'],
+    target: 'browser',
+    minify,
+  });
+  if (!result.success) {
+    for (const log of result.logs) console.error(log);
+    throw new Error('bundle failed');
+  }
+  let js = await result.outputs[0].text();
+  // Guard against a literal </script> inside the bundle closing our tag early.
+  js = js.replaceAll('</script', '<\\/script');
+  const css = await Bun.file('./src/style.css').text();
+
+  return `<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
+<meta name="color-scheme" content="light">
+<title>Bitcoin Wallet</title>
+<link rel="icon" href="${FAVICON}">
+<style>${css}</style>
+</head>
+<body>
+<div id="app"></div>
+<script>${js}</script>
+</body>
+</html>`;
+}
+
+if (import.meta.main) {
+  await mkdir('dist', { recursive: true });
+  const html = await buildHtml({ minify: true });
+  await Bun.write('dist/index.html', html);
+  const kb = (Buffer.byteLength(html) / 1024).toFixed(0);
+  console.log(`✓ dist/index.html written (${kb} KB) — open it offline, no server needed`);
+}