Add regtest network support

New `regtest` network (bech32 `bcrt`, testnet version bytes) selectable in
Settings, pointed at a configurable local Esplora (default http://localhost:3000).
Adds getNetwork/setNetwork + getRegtestEsplora persistence, a regtest branch in
resolveHosts, mainnet-only gating for the realtime watcher + Electrum backend,
and a Network selector card. Account loading reads the active network.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

3 files changed, 82 insertions, 8 deletions

diff --git a/src/api.js b/src/api.js
index 6f010cb..d135218 100644
--- a/src/api.js
+++ b/src/api.js
@@ -32,8 +32,37 @@ export function setExplorerConfig({ server, url }) {
   } catch {}
 }
 
+// Active Bitcoin network (mainnet | testnet | regtest), persisted globally.
+const NETWORK_KEY = 'btc-wallet-network';
+export function getNetwork() {
+  try {
+    const n = localStorage.getItem(NETWORK_KEY);
+    if (n === 'mainnet' || n === 'testnet' || n === 'regtest') return n;
+  } catch {}
+  return 'mainnet';
+}
+export function setNetwork(net) {
+  try { localStorage.setItem(NETWORK_KEY, net); } catch {}
+}
+
+// Regtest points at a local Esplora-compatible server (coinos's chopsticks `cs`
+// at :3000 by default). Treated like a self-hosted custom explorer: the URL is
+// used as the esplora base directly (no `/api` prefix, no `/testnet`).
+const REGTEST_ESPLORA_KEY = 'btc-wallet-regtest-esplora';
+export function getRegtestEsplora() {
+  try { return (localStorage.getItem(REGTEST_ESPLORA_KEY) || '').trim() || 'http://localhost:3000'; }
+  catch { return 'http://localhost:3000'; }
+}
+export function setRegtestEsplora(url) {
+  try { localStorage.setItem(REGTEST_ESPLORA_KEY, (url || '').trim()); } catch {}
+}
+
 // Resolve the configured explorer to the host list the Api tries in order.
 function resolveHosts(net) {
+  if (net === 'regtest') {
+    const base = getRegtestEsplora().replace(/\/+$/, '');
+    return [{ base, kind: 'esplora', web: base, cooldownUntil: 0 }];
+  }
   const cfg = getExplorerConfig();
   const apiPath = net === 'testnet' ? '/testnet/api' : '/api';
   const host = (web, kind) => ({ base: web + apiPath, kind, web, cooldownUntil: 0 });
@@ -138,7 +167,7 @@ export function resolveElectrumUrl() {
 }
 
 export function wsUrl(net) {
-  if (net === 'testnet') return null;
+  if (net !== 'mainnet') return null; // coinos watcher is mainnet-only
   // Electrum backend selects/rotates candidates in the wallet; here we only
   // resolve the coinos watcher (esplora 'coinos' mode) or null (esplora 'explorer').
   if (getBackend() === 'electrum') return null;
@@ -182,6 +211,8 @@ export class Api {
     return web + (this.net === 'testnet' ? '/testnet/tx/' : '/tx/') + txid;
   }
 
+  get isRegtest() { return this.net === 'regtest'; }
+
   // ---- rate-aware global scheduler --------------------------------------
   #schedule(task) {
     return new Promise((resolve, reject) => {
diff --git a/src/app.js b/src/app.js
index 99343f7..1dbd478 100644
--- a/src/app.js
+++ b/src/app.js
@@ -8,7 +8,7 @@ import { Wallet, newMnemonic, isValidMnemonic, accountXpubFor, cacheKeyFor, utxo
 import { qrSvg } from './qr.js';
 import { scanQr } from './scan.js';
 import { getSyncConfig, setSyncConfig } from './nostr.js';
-import { getExplorerConfig, setExplorerConfig, EXPLORER_PRESETS, getDataMode, setDataMode, ELECTRUM_PRESETS, getElectrumServerConfig, setElectrumServerConfig } from './api.js';
+import { getExplorerConfig, setExplorerConfig, EXPLORER_PRESETS, getDataMode, setDataMode, ELECTRUM_PRESETS, getElectrumServerConfig, setElectrumServerConfig, getNetwork, setNetwork, getRegtestEsplora, setRegtestEsplora } from './api.js';
 import { isSilentPaymentAddress } from './silentpay.js';
 import { t, LANGS, getLang, setLang, isRTL, loadLocale } from './i18n.js';
 import {
@@ -629,9 +629,10 @@ async function activateAccount(acc, opts = {}) {
   // until the user commits (claims, or chooses to keep it / enters the wallet),
   // so bailing from an already-claimed gift doesn't leave an empty account.
   if (opts.gift) acc.provisional = true;
-  if (acc.type === 'watch') wallet.load({ xpub: acc.xpub, netName: 'mainnet', offline: false });
-  else if (acc.xprv) wallet.load({ xprv: acc.xprv, netName: 'mainnet', offline: false });
-  else wallet.load({ mnemonic: acc.mnemonic, passphrase: acc.passphrase || '', netName: 'mainnet', offline: false });
+  const netName = getNetwork();
+  if (acc.type === 'watch') wallet.load({ xpub: acc.xpub, netName, offline: false });
+  else if (acc.xprv) wallet.load({ xprv: acc.xprv, netName, offline: false });
+  else wallet.load({ mnemonic: acc.mnemonic, passphrase: acc.passphrase || '', netName, offline: false });
   // Record the account-level xpub so this wallet survives a session wipe as a
   // watch-only entry (see the durable account directory) — you keep seeing your
   // balance/history and re-enter the seed to spend again.
@@ -1140,7 +1141,7 @@ function lock() {
   wallet.stopRealtime();
   clearAccounts();
   vaultPassword = null;
-  wallet.load({ mnemonic: '', passphrase: '', netName: 'mainnet', offline: false });
+  wallet.load({ mnemonic: '', passphrase: '', netName: getNetwork(), offline: false });
   wallet.mnemonic = '';
   ui.screen = hasVault() ? 'vault' : 'unlock';
   ui.unlockTab = 'create';
@@ -1320,6 +1321,7 @@ function settingsTab() {
         : h('button', { onClick: () => { ui.addrScan = true; ui.addrScanPage = 0; render(); } }, t('rescanAddresses'))
     ),
     autoLockCard(),
+    networkCard(),
     explorerCard(),
     wallet.watchOnly || !wallet.mnemonic ? null : syncCard()
   );
@@ -1551,6 +1553,43 @@ function autoLockCard() {
   );
 }
 
+// Switch the active Bitcoin network. Changes addresses/balances entirely, so we
+// persist the choice and reload the active account (or empty wallet) under it.
+function changeNetwork(net) {
+  if (net === getNetwork()) return;
+  setNetwork(net);
+  const acc = accounts.find((a) => a.id === activeId);
+  if (acc) activateAccount(acc); else render();
+}
+
+// Network selector (mainnet / testnet / regtest). Regtest also exposes the
+// Esplora base URL (default coinos chopsticks at http://localhost:3000).
+function networkCard() {
+  const net = getNetwork();
+  return h(
+    'div',
+    { class: 'card col' },
+    h('h3', {}, 'Network'),
+    h('p', { class: 'small muted', style: 'margin:0' }, 'Bitcoin network this wallet operates on.'),
+    h('select', { onChange: (e) => changeNetwork(e.target.value) },
+      h('option', { value: 'mainnet', selected: net === 'mainnet' }, 'Mainnet'),
+      h('option', { value: 'testnet', selected: net === 'testnet' }, 'Testnet'),
+      h('option', { value: 'regtest', selected: net === 'regtest' }, 'Regtest')
+    ),
+    net === 'regtest'
+      ? h('label', { class: 'field' },
+          h('span', { class: 'lab' }, 'Regtest Esplora URL'),
+          h('input', {
+            type: 'text', class: 'mono-input', placeholder: 'http://localhost:3000',
+            autocapitalize: 'none', autocomplete: 'off', spellcheck: 'false', value: getRegtestEsplora(),
+            onChange: (e) => { setRegtestEsplora(e.target.value.trim()); wallet.reloadExplorer(); },
+          }),
+          h('div', { class: 'small faint' }, 'Esplora-compatible REST endpoint (coinos chopsticks/electrs).')
+        )
+      : null
+  );
+}
+
 function explorerCard() {
   const mode = getDataMode();
   const cfg = getExplorerConfig();
diff --git a/src/wallet.js b/src/wallet.js
index 33a1f3f..a721c00 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -41,6 +41,9 @@ const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
 const NETS = {
   mainnet: { net: btc.NETWORK, coin: 0 },
   testnet: { net: btc.TEST_NETWORK, coin: 1 },
+  // Regtest shares testnet's version bytes / coin type; only the bech32 HRP
+  // differs (`bcrt`). @scure/btc-signer derives addresses + validates from this.
+  regtest: { net: { ...btc.TEST_NETWORK, bech32: 'bcrt' }, coin: 1 },
 };
 
 export function newMnemonic(strengthBits = 128) {
@@ -192,7 +195,7 @@ export class Wallet {
       this.api = new ElectrumApi({
         call: (m, p) => this._rpcCall(m, p),
         network: this.netCfg.net,
-        testnet: this.netName === 'testnet',
+        testnet: this.netName !== 'mainnet',
         explorerWeb: explorerWeb(),
       });
     } else {
@@ -1266,7 +1269,8 @@ export class Wallet {
   // and balances update with no polling.
   wsUrl() {
     // Electrum backend: pick the current failover candidate (rotated on failure).
-    if (getBackend() === 'electrum' && this.netName !== 'testnet') {
+    // Electrum is mainnet-only here; testnet/regtest use esplora + polling.
+    if (getBackend() === 'electrum' && this.netName === 'mainnet') {
       if (!this._wsCandidates || !this._wsCandidates.length) { this._wsCandidates = electrumCandidates(); this._wsCandIdx = 0; }
       const list = this._wsCandidates;
       return list.length ? list[(this._wsCandIdx || 0) % list.length] : null;