Add Boltz submarine + reverse swaps (Lightning <-> on-chain)

Non-custodial swaps via Boltz, fully client-side: hal holds the swap key +
preimage and claims (reverse) / refunds (submarine) on-chain via the taproot
script path, so Boltz can never strand funds.

- src/swap.js: tapleaf/tree construction (byte-exact vs boltz-core vectors),
  swap P2TR address derivation (MuSig2 internal key + taptweak), script-path
  claim/refund tx builder, bolt11 decode, Boltz api-v2 client, and a polling
  SwapManager (reverse auto-claim; submarine fund + status + refund).
- wallet.js: deterministic swap-key derivation (dedicated chain) + persistence.
- api.js: configurable Boltz REST/WS endpoints.
- app.js: ⚡ Swap tab — Receive over LN (reverse) + Pay an invoice (submarine).
- tools/swap-*.test.js: vectors, live-address, and end-to-end regtest tests.

Verified end-to-end on regtest against a local Boltz wired to coinos's bc +
a dedicated CLN/hold node.

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

1 files changed, 15 insertions, 0 deletions

diff --git a/src/api.js b/src/api.js
index d135218..d6fa2ee 100644
--- a/src/api.js
+++ b/src/api.js
@@ -57,6 +57,21 @@ export function setRegtestEsplora(url) {
   try { localStorage.setItem(REGTEST_ESPLORA_KEY, (url || '').trim()); } catch {}
 }
 
+// Boltz swap backend endpoints (regtest defaults; the api-v2 REST + the
+// sidecar swap-status WebSocket). Overridable in Settings for staging/mainnet.
+const BOLTZ_API_KEY = 'btc-wallet-boltz-api';
+const BOLTZ_WS_KEY = 'btc-wallet-boltz-ws';
+export function getBoltzApi() {
+  try { return (localStorage.getItem(BOLTZ_API_KEY) || '').trim() || 'http://localhost:9001'; }
+  catch { return 'http://localhost:9001'; }
+}
+export function getBoltzWs() {
+  try { return (localStorage.getItem(BOLTZ_WS_KEY) || '').trim() || 'ws://localhost:9004/v2/ws'; }
+  catch { return 'ws://localhost:9004/v2/ws'; }
+}
+export function setBoltzApi(url) { try { localStorage.setItem(BOLTZ_API_KEY, (url || '').trim()); } catch {} }
+export function setBoltzWs(url) { try { localStorage.setItem(BOLTZ_WS_KEY, (url || '').trim()); } catch {} }
+
 // Resolve the configured explorer to the host list the Api tries in order.
 function resolveHosts(net) {
   if (net === 'regtest') {