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, 20 insertions, 0 deletions

diff --git a/src/wallet.js b/src/wallet.js
index a721c00..94132a6 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -1088,6 +1088,26 @@ export class Wallet {
   _saveReclaimed() {
     try { localStorage.setItem(this._reclaimedKey(), JSON.stringify([...this.reclaimedSet()])); } catch {}
   }
+
+  // ---- Boltz swap support ----------------------------------------------
+  // Persisted swap records (public metadata only — keys/preimage are re-derived
+  // deterministically from the seed via swapNode, so nothing secret is stored).
+  _swapKey() { return this._cacheKey() + ':swaps'; }
+  loadSwaps() {
+    try { return JSON.parse(localStorage.getItem(this._swapKey()) || '[]'); } catch { return []; }
+  }
+  saveSwaps(list) {
+    try { localStorage.setItem(this._swapKey(), JSON.stringify(list)); } catch {}
+  }
+  nextSwapIndex() {
+    return this.loadSwaps().reduce((m, s) => Math.max(m, (s.swapIndex ?? -1) + 1), 0);
+  }
+  // Deterministic swap keypair on a dedicated chain (2) so swap keys never
+  // collide with receive (0) / change (1). Returns the HDKey node (has
+  // privateKey + publicKey, 33-byte compressed).
+  swapNode(index) {
+    return this.account().deriveChild(2).deriveChild(index);
+  }
   // Passive reclaim: free the coin for spending but keep tracking the live link
   // so it can still be revoked later (until the coin is spent).
   unreserve(id) {