Use Fulcrum (Electrum/WS) for regtest data + push, dropping esplora

Regtest now talks to a local Fulcrum over its native Electrum WebSocket for
both chain data and realtime push, instead of esplora REST + a separate watcher.
This matches prod (Fulcrum) and gives ~2-3x lower latency than the previous
electrs polling. getBackend()/electrumCandidates() route regtest to the
Electrum backend at the configured Fulcrum WS (default ws://localhost:50003);
the wallet's realtime path is ungated for regtest. ElectrumApi already covers
every call (utxos, history, fees, broadcast), incl. the swap feature.

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

2 files changed, 6 insertions, 2 deletions

diff --git a/src/api.js b/src/api.js
index 98b7528..bcc5f85 100644
--- a/src/api.js
+++ b/src/api.js
@@ -119,6 +119,9 @@ export const COINOS_ELECTRUM = false;
 const COINOS_ELECTRUM_URL = 'wss://coinos.io/electrum';
 
 export function getBackend() {
+  // Regtest runs Fulcrum (Electrum over WS) for both data and realtime push —
+  // matches prod and drops the esplora/electrs dependency.
+  if (getNetwork() === 'regtest') return 'electrum';
   const m = getDataMode();
   if (m === 'electrum') return 'electrum';
   if (m === 'coinos' && COINOS_ELECTRUM) return 'electrum';
@@ -156,6 +159,7 @@ export function setElectrumServerConfig({ server, url }) {
 // addresses to a public server you didn't pick.
 const PUBLIC_ELECTRUM = () => ELECTRUM_PRESETS.filter((x) => x.url).map((x) => x.url);
 export function electrumCandidates() {
+  if (getNetwork() === 'regtest') return [getRegtestElectrumWs()]; // local Fulcrum
   if (getDataMode() === 'coinos' && COINOS_ELECTRUM) return [COINOS_ELECTRUM_URL, ...PUBLIC_ELECTRUM()];
   const cfg = getElectrumServerConfig();
   if (cfg.server === 'custom') return cfg.url.trim() ? [cfg.url.trim()] : [];
diff --git a/src/wallet.js b/src/wallet.js
index a721c00..a3b2429 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -1269,8 +1269,8 @@ export class Wallet {
   // and balances update with no polling.
   wsUrl() {
     // Electrum backend: pick the current failover candidate (rotated on failure).
-    // Electrum is mainnet-only here; testnet/regtest use esplora + polling.
-    if (getBackend() === 'electrum' && this.netName === 'mainnet') {
+    // Mainnet (when cut over to Fulcrum) and regtest (local Fulcrum) use Electrum.
+    if (getBackend() === 'electrum' && (this.netName === 'mainnet' || this.netName === 'regtest')) {
       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;