Add Electrum-over-WebSocket as an alternative data backend

Settings → Data source now offers 'Electrum' alongside the Esplora REST explorer.
One Electrum WebSocket serves BOTH the wallet's data queries and scripthash push
notifications, so pointing Hal at your own Fulcrum/electrs gives a fully
self-hosted setup — no coinos, no public REST, nothing shared off your node.

- src/electrum.js: ElectrumApi maps the Esplora shapes the wallet consumes onto
  Electrum methods (scripthash get_balance/listunspent/get_history, estimatefee,
  transaction.broadcast). electrs has no verbose tx lookup, so it parses raw txs
  and resolves input values from parent txs to compute fees (cached, in-flight
  deduped, bounded-parallel). Validated field-for-field against mempool.space:
  addressTxs (fee/vin/vout/status), getTx, outspend, balance, utxos.
- wallet.js: the realtime socket already spoke Electrum's notify protocol; added
  request/response (_rpcCall) so the same connection answers data calls. Real
  Electrum notifications carry no tx data, so they reconcile via the backend.
  Replaced the fragile newline parser with a string-aware brace-depth scanner
  that handles every framing (newline, one-per-frame, concatenated, split) —
  fixes a buffer-poisoning hang under concurrent calls; also hardens the coinos
  watcher path. Esplora stays the default; nothing changes for existing users.

Verified end-to-end against blockstream's electrs: concurrent transport, a full
fresh-wallet scan (~2s), and the parser unit-tested on all framings.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

0 files changed, 0 insertions, 0 deletions